Conformational control over π-conjugated electron pairing in 1D organic polymers

During the past decades π-conjugated bi-radicals have attracted increasing attention, due to the existence of two close-in-energy resonant electronic configurations with very distinct characteristics: the open-shell bi-radical and the closed-shell quinoidal. The chemical design of the bi-radical structure has been shown to be very effective to shift the balance towards one, or the other, electronic distribution. Some reports have experimentally studied the analogous 1D oligomers and polymers, however, only the open-shell multi-radical configuration has been detected, and it is yet not very clear which structural and chemical parameters are relevant in such extended systems. In this work, via first principles quantum chemical simulations, we study a series of π-conjugated 1D polymers based on triarylmethyl radicals with different chemical functionalization. We find that dihedral angles of the aryl rings connecting the radical centres are the key conformational parameter determining the electronic balance. This provides a simple recipe to use chemical functionalization of aryl rings as a tool to shift the system towards either the electron paired or unpaired configurations. Additionally, we find such conformational control is also effective under the effect of thermal fluctuations, which highlights its potential technological applicability.

Chemically designed conformational changes are shown to act as effective tools to induce electron pairing in otherwise multiradical 1D organic polymers.     

A new metallic π-conjugated carbon sheet used for the cathode of Li–S batteries

Lithium–sulfur (Li–S) batteries are considered as the most promising next generation high density energy storage devices. However, the commercialization of Li–S batteries is hindered by the shuttle effect of polysulfides, the low electronic conductivity of the sulfur cathode and a large volume expansion during lithiation. Herein, we predict a new two dimensional sp² hybridized carbon allotrope (PHE-graphene) and prove its thermodynamic and kinetic stability. If it is utilized to encapsulate the cathode of Li–S batteries, not only will the shuttle effect be avoided but also the electronic conductivity of the sulfur cathode will be improved significantly owing to its metallic electronic band structure. The thermal conductivity of PHE-graphene was found to be very high and even comparable with graphene, which is helpful for the heat dissipation of cathodes. In addition, PHE-graphene also exhibited superior mechanical properties including ideal tensile strength and in-plane stiffness.

A metallic carbon sheet was used for the cathode of Li–S batteries to eliminate the shuttle effect and improve cathode electric conductivity.     

Donor–acceptor random regioregular π-conjugated copolymers based on poly(3-hexylthiophene) with unsymmetrical monothienoisoindigo units

Donor–acceptor π-conjugated random copolymers based on regioregular poly(3-hexylthiophene), rr-P3HT, with unsymmetrical monothienoisoindigo moieties were obtained by direct arylation polycondensation of 2-bromo-3-hexylthiophene with unsymmetrical monothienoisoindigo motifs under the optimized conditions [palladium-immobilized on thiol-modified silica gel with chloride counter anions, PITS-Cl (2.5 mol%), PivOH (1.0 equiv.), K₂CO₃ (3.0 equiv.), DMAc, 100 °C, 24 h]. Incorporation of unsymmetrical monothienoisoindigo electron-acceptor units into the polymers tuned their highest occupied and lowest unoccupied molecular orbital levels, which were close to those of the hole transport material (PEDOT) and electron transport material (PCBM), respectively, in thin-film organic solar cells. Alkyl chains of the unsymmetrical monothienoisoindigo units in the polymers tuned their macrostructural order, resulting in the observation of crystalline patterns and specific absorption peaks in thin films. An organic solar cell containing the most crystalline random copolymer showed an efficiency of 1.91%.

Donor–acceptor π-conjugated random copolymers based on regioregular poly(3-hexylthiophene) with unsymmetrical monothienoisoindigo moieties were obtained by direct arylation polycondensation.     

Constructing “breathing” dynamic skeletons with extra π-conjugated adsorption sites for iodine capture

Radioiodine (¹²⁹I and ¹³¹I) emission from the nuclear waste stream has aroused enormous apprehension because of its quick diffusion and radiological contamination. Conventional porous adsorbents such as zeolites and carbon with rigid skeletons and constant pore volumes reveal a limited performance for reliable storage. Here, a series of soft porous aromatic frameworks (PAFs) with additional π-conjugated fragments is disclosed to serve as physicochemical stable media. Due to the flexibility of the tertiary amine center, the PAF products provide sufficient space for the binding sites, and thus exhibit a considerable capability for iodine capture from both gaseous and soluble environments. The obtained capacity of PAFs is ca. 1.6 times higher than that of PAF-1 which possesses similar aromatic constituents featuring an ultra-large specific surface area (BET = 5600 m² g⁻¹). The novel paradigm of dynamic frameworks is of fundamental importance for designing adsorbents to treat environmental pollution issues.

A series of soft porous aromatic frameworks (PAFs) with additional π-conjugated fragments provides sufficient space for the binding sites which serve as physicochemical stable mediums for radioiodine.

With the rapid development of the nuclear industry, a large amount of volatile radionuclides (¹²⁹I, ¹³¹I, ³H, ⁸⁵Kr etc.) accompanying nuclear fission are effused into the atmosphere.¹ Radioiodine with high volatility and long radioactive half-life (1.57 × 10⁷ years) attracts particular attention because its sustained pernicious effects on human metabolism ultimately result in an increased incidence of thyroid cancer.^2–4 In this regard, great efforts have been focused on adsorbents to effectively capture and store radioactive iodine for safety and accessibility in the use of nuclear energy.^5,6 Typical nuclear fuel processing conditions are under ambient pressure and 350 K where iodine exists as a coagulative vapor (diameter 5.4 Å).⁷ Therefore, iodine uptake in porous materials mostly depends on the binding sites and pore volume.⁸ However, the traditional adsorbents including zeolites, carbon, and inorganic–organic hybrid porous materials (MOFs, PCPs etc.) possess a narrow pore size and finite volume in their rigid skeletons.^9–19 Their settled pore space can be occupied by iodine as the maximum accessibility of 50%, which generates confined iodine capacity.^7,20 To achieve zero emission of radio-active vapors, the development of high-performance porous materials is desperately urgent.Organic porous frameworks constructed by organic building units through covalent bonds are emerging as novel porous solids.^21–27 Due to the low density, high stability, and large surface area, these functional products have made a probable promise in the field of gas storage, energy conversion, catalysis, and optoelectronics.^28–36 Porous aromatic frameworks (PAFs) as an amorphous representative are well-known for their stable skeletons and large surface areas.³⁷ Based on the advanced organic chemistry, one is able to prepare versatile PAFs with tunable organic composition and tailored structure.³⁸ Their salient characteristics motivate wide interests in the design and synthesis of unique porous skeletons to challenge the traditional rigid frameworks for radioiodine adsorption.In this contribution, we prepared a class of tertiary amine centered PAF materials (LNU 1–4, LNU represents Liaoning University) via a Suzuki coupling reaction. Unlike the traditional porous adsorbents, the N linked aromatic fragments could be distorted and triggered into a “breathing” dynamic skeleton for fitting iodine storage.^39–44 Besides, various π-conjugated units were incorporated into the architecture to serve as adsorption sites. Consequently, the soft PAFs with dynamic architectures render a significant adsorption for iodine molecules and enable cycle use for many times while retaining their high capacity.As illustrated in Scheme 1, LNU-1, LNU-2, LNU-3, and LNU-4 were synthesized by polycondensation reactions of 4-(tetramethyl-1,3,2-dioxaborolan-2-yl)-N,N-bis-[4-(tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl]aniline (BBA) with respective dibromo monomer (2,7-dibromofluorene, 1,4-dibromonaphthalene, 2,6-dibromonaphthalene and 9,10-dibromoanthracene, respectively). According to the Fourier transform infrared spectroscopy (FTIR) spectra (Fig. S1^†), the disappearance of C–Br stretching vibration frequency (500 cm⁻¹), C–B vibration band (1417 cm⁻¹), and B–O vibration band (1351 cm⁻¹) from the initial building blocks indicates the completion of cross-coupling reactions and suggests the formation of porous polymers. The structural details of LNU 1–4 networks were also characterized at the molecular level by solid-state ¹³C NMR spectroscopy (Fig. S2^†). The major peaks observed at 135–150 ppm could be assigned to the C substituted aromatic carbons and signals in the range of 120–135 ppm are ascribed to the H coupled aromatic carbons, respectively. Powder X-ray diffraction (PXRD) pattern (Fig. S3^†) shows that all PAF samples possess no long-range ordered structure. Scanning electron microscopy (SEM) indicates these resultants are composed of aggregated spheres in micrometer size (Fig. S4^†). The worm-like patterns from transmission electron microscopy (TEM) manifest the amorphous textures of LNU 1–4 which is coincident with the PXRD conclusion (Fig. S5^†).Open in a separate windowScheme 1Synthetic routes for PAF materials LNU-1, LNU-2, LNU-3, and LNU-4 via a Suzuki coupling reaction.The stability and porosity of adsorbents are critical factors for the practical molecular storage application. The four polymers are stable up to 350 °C assessed by thermogravimetric analysis (TGA) in air atmosphere (Fig. S6^†). Also there is no weight loss after immersing PAF powders into a variety of common organic solvents, such as DMF, THF, acetone, and CHCl₃, respectively, proving the excellent chemical stability of PAFs. The porosities of LNU 1–4 products were evaluated by nitrogen gas adsorption and desorption experiments at 77 K. As shown in Fig. S7,^† all resultants show almost no gas sorption at relatively low pressure (P/P₀ < 0.9), and show Type-III isotherms indicating the weak adsorbate–adsorbent interactions.^45,46 The specific surface areas calculated by the BET equation are 26, 20, 30, and 24 m² g⁻¹ for LNU-1, LNU-2, LNU-3, and LNU-4, respectively. Meanwhile, the CO₂ isotherms at 273 K and 298 K reveal a typical CO₂ adsorption behaviour (Fig. S8^†). As illustrated from CO₂ desorption, all four LUN materials show a hysteretic behavior, which together with the relatively large capacity is the typical character of “breathing” adsorbents. This result suggests that the adsorption mechanism of LNUs preceeds the guest-responsive structural rearrangements and realized the “dynamic” skeletons.^47–49 This phenomenon is attributed to that the N linked aromatic fragments could be distorted leading to a soft skeleton which tends to collapse into a dense, non-porous solid.^50,51The traditional rigid adsorbents with a constant porosity exhibit the limited iodine capacity, such as porous silver-doped zeolite mordenite (Ag-MOR), carbon (Cg-5P), and zeolitic imidazolate framework-8 (ZIF-8) possess the slight iodine capacities of 0.07, 0.28, and 1.25 g g⁻¹, respectively.⁷ For purposes of comparison, the novel PAF materials with excellent stability and soft architecture were carried out the iodine enrichment experiments by exposing the powder samples into iodine vapor. As shown in Fig. 1 and S9,^† LNU-1 without accessible porosity for N₂ molecules could adsorb 2.49 g g⁻¹ iodine molecules. As a reference, PAF-1 possesses similar chemical constituents of multiple benzene rings as LNU-1, but a carbon center and high porosity (BET surface area = 5600 m² g⁻¹), which only adsorbs 1.86 g g⁻¹ iodine.⁵² As known, the expanded conjugated network together with the electron-rich characteristic of triphenylamine units possesses strong affinity with I₂ molecules.^15,19,52 For non-porous PAF skeleton (LNU-1), this outstanding iodine uptake implies that the dense structure generates a specific dynamic configuration transformation and is triggered into a “breathing” state due to the flexibility of triphenylamine fragment, which favours the access and storage of iodine molecules.^51,53,54Open in a separate windowFig. 1Iodine uptake of the LNU-1 as a function of exposure time. Photograph for PAF powder LNU-1 before and after iodine capture (inset).To confirm this speculation, all PAF samples after performed the iodine adsorption procedure were conducted by the TGA analysis. As shown in Fig. 2a, there is a gradual mass loss started from 90 °C and ended at 200 °C, which suggests the strong affinity of iodine with PAF architecture (I₂ boiling point is 184 °C). In addition, we conducted FT-IR, PXRD, and Raman analyses for PAFs after it absorbed I₂ molecules, with the resultant material named PAF-I₂. As illustrated in Fig. 2b, the special bands of C C and C–H in the phenyl ring change from 1504 and 819 cm⁻¹ to 1502 and 822 cm⁻¹, respectively, demonstrating the interaction of aromatic fragments with I₂ molecules.⁵⁵ There are no characteristic peaks of elemental iodine in the PXRD patterns compared with I₂ and PAF-I₂ which demonstrates the uniform distribution of iodine molecules in LNU-1 framework (Fig. 2c). Furthermore, the strong peaks at 113 and 173 cm⁻¹ recorded by Raman spectroscopy manifest the I₅⁻ state of adsorbed iodine molecules, which is attributed to the charge transfer between the electron-deficient guest iodine molecules and the electron-rich host network at high coverage (Fig. 2d).^55,56 All these results demonstrate the adsorbed I₂ molecules are uniformly distributed in the PAF architecture suggesting the dynamic configuration transformation of PAF skeleton for fitting the I₂ storage.Open in a separate windowFig. 2(a) TGA curve of the iodine adsorbed LNU-1. FT-IR spectra (b), PXRD profiles (c), and Raman spectra (d) of the LNU-1 and iodine adsorbed LNU-1.This “breathing” dynamic skeleton of LNU-1 prompted us a further investigate to achieve a better performance for radioiodine capture. Various π-conjugated groups including naphthalene and anthracene rings are introduced into the soft framework. In accordance with analysis above, naphthalene based LNU-2 and LNU-3 and anthracene based LNU-4 exhibit a similar “breathing” state which is demonstrated by the TGA, FT-IR, PXRD, and Raman spectra (Fig. S10–S13^†). The PAF resultants reveal increased iodine uptake capacities of 2.95 g g⁻¹ for LNU-2 and 2.76 g g⁻¹ for LNU-3, respectively from 2.49 g g⁻¹ for LNU-1. This increased capacity is attributed to the flexible skeleton provides sufficient space for the accessibility of iodine to π-conjugated groups which possess a strong affinity for guest binding through charge transfer.^55–57 Furthermore, two increased FT-IR peaks of conjugated group located at 1258 and 1159 cm⁻¹ and the emerging Raman signals at 110 and 175 cm⁻¹ demonstrate this charge transfer from the highest occupied molecular orbital (HOMO) of π-conjugated group to the lowest unoccupied molecular orbital (LUMO) of iodine.⁴⁵ As to LNU-4 (2.04 g g⁻¹ iodine uptake), the anthracene constituent with a similar binding structure as naphthalene group increases the weight of structural unit resulting in the reduced maximum I₂ capacity compared with LNU-2 and LNU-3. Due to the elaborate design, the tertiary amine centered PAF materials express a better performance than the classical microporous polymers including PAF-21 (1.52 g g⁻¹), PAF-23 (2.71 g g⁻¹), pha-HcoP-1 (1.31 g g⁻¹), NAPOP-1 (2.06 g g⁻¹), NIP-CMP (2.02 g g⁻¹), CMPN-3 (2.08 g g⁻¹), and SCMP-1 (1.88 g g⁻¹).^{18,19,58–61}Additionally, the iodine sorption experiments of PAF products were exploited in the iodine containing solution. When PAFs were immersed in a hexane solution of iodine (C = 1000 mg L⁻¹) at room temperature, the dark purple solutions fade gradually to colourless status (Fig. 3a and S14^†). This phenomenon indicates the porous frameworks with strong affinity could be utilized to extract iodine molecules from the liquid environments. Notably, the LNU PAFs could be activated upon the thermal treatment at 398 K for 120 min of iodine-captured PAF samples. Also the iodine adsorbed porous skeletons release the guest molecules by immersing the resultants in organic solvents at room temperature (Fig. 3b and S15^†). The soft PAF materials are recyclable after the activation at 398 K and 120 min, while retaining a considerable uptake capacity after five cycles (Fig. S16^†). All these results demonstrate the tertiary amine centered PAF materials possess tremendous potential for iodine capture application compared to the conventional adsorbents.Open in a separate windowFig. 3Photographs indicate the gradual changes in iodine adsorption (a) and desorption (b) processes of LNU-1.     

N-Aryl iminochromenes inhibit cyclooxygenase enzymes via π–π stacking interactions and present a novel class of anti-inflammatory drugs

Cyclooxygenase enzymes (COX1/2) have been widely studied and noted for their role in the biosynthesis of inflammation-induced proteins, prostaglandins and thromboxane. Multiple anti-inflammatory drugs have been developed to target these two enzymes, but most of them appeared to have notable adverse effects, especially on the cardiovascular system and lower gastrointestinal tract, suggesting an urgent need for new potent anti-inflammatory drugs. In this study, we screened twenty-two previously synthesized N-aryl iminochromenes (NAIs) for their anti-inflammatory activity by performing COX-1/2 inhibitory assays. Five compounds (1, 10, 14, 15, and 20) that gave the best in vitro anti-inflammatory results were subjected to an in vivo anti-inflammatory assay using the formalin-induced hind rat paw oedema method, followed by in silico studies using indomethacin and celecoxib as standard drugs. Among them, compound 10 stood out as the best candidate, and the percentage reduction in paw oedema at the dose of 20 mg kg⁻¹ body weight was found to be substantially higher with compound 10 than that with indomethacin. This is mostly due to the excellent suitability of the chromene-phenyl scaffold with a highly concentrated area of aromatic residues, which produced good π–π stacking interactions. Taken together, this study strongly suggests compound 10 as a potential candidate for anti-inflammatory drug research.

Screening of N-aryl iminochromenes for their anti-inflammatory activities by performing in vitro, in vivo, and in silico studies.     

Facile synthesis of aminated indole-based porous organic polymer for highly selective capture of CO2 by the coefficient effect of π–π-stacking and hydrogen bonding

A new aromatic aminated indole-based porous organic polymer, PIN-NH₂, has been successfully constructed, and it was demonstrated that the coefficient effect endows this porous material with outstanding CO₂ absorption capacity (27.7 wt%, 1.0 bar, 273 K) and high CO₂/N₂ (137 at 273 K and 1 bar) and CO₂/CH₄ (34 at 273 K and 1 bar) selectivity.

It was demonstrated that the coefficient effect endows POP PIN-NH₂ with outstanding CO₂ absorption capacity and high selectivity.

Today, one of the most serious environmental problems is climate change, such as global warming and sea-level rises, which are caused by increased concentrations of carbon dioxide (CO₂) in the atmosphere.^1–3 As we all know, CO₂ mainly arises from fossil-fuel combustion in power plants, and the flue gas is always mixed with other gases including nitrogen (N₂), methane (CH₄) and so on. Therefore, it is necessary to design materials for selectively separating and adsorbing CO₂ from these industrial and energy-related sources to improve the environmental problems.^4–6 Aqueous amine solutions are the most common adsorbents for CO₂ separation and capture,⁷ however, not only do these adsorbents degrade over time and are corrosive, toxic, and volatile, but also the regeneration process is highly energy demanding for these systems due to the chemical capture mechanism. As alternatives, porous organic polymers (POPs)^8–10 relying on physical adsorption have become the research focus due to their low density, large specific surface area, good thermal stability, and narrow pore size distribution, but the low uptake capacity, and especially, the poor selectivity are two urgent issues that need to be addressed that seriously restrict the commercialization of POP adsorbents.¹¹ Hence, in the past few years, many methods have been developed to improve the POP performance including increasing the surface area and adjusting the pore size.^12,13Recently, based on the rapid development of supramolecular interactions^14,15 and the unique advantage of POP materials, i.e., the structure designability, researchers found that introducing special active sites into the framework, such as heteroatoms and diverse organic groups, is a simple and effective way to ameliorate the adsorption performance by the formation of some special non-covalent interactions and various functional groups have been explored.^16–18 Recently, Chang et al.¹⁹ have designed and prepared an novel aerogel (PINAA) that contains both amide and indole groups and they demonstrated that the CO₂ can be rapidly adsorbed on the heteroaromatic ring of indole because of its relatively large binding area via strong π–π-stacking interactions, and then, the desorbed CO₂ molecule can be captured by an adjacent amide group because of “electrostatic in-plane” interaction. This synergistic effect of electrostatic in-plane and dispersive π–π-stacking interactions of amide and indole with CO₂ endows the resulting aerogel enhanced CO₂ adsorption capacity and CO₂/CH₄ and CO₂/N₂ selectivity. Inspired by this fascinating study, we hypothesized that when the indole group is aminated, the CO₂ can be rapidly adsorbed on the heteroaromatic ring of indole because of its relatively large binding area via strong π–π-stacking interaction (Fig. 1a), after that, the hydrogen bonding interactions between the O of the CO₂ and –NH of the aniline group would make the CO₂ to further form a stable conformation with the aminated indole system (Fig. 1b), as a result, the coefficient effect of π–π-stacking interactions and hydrogen bonding interactions would ensure the high CO₂ adsorption capacity and further enhanced CO₂/CH₄ and CO₂/N₂ selectivity.Open in a separate windowFig. 1Schematic representation showing the heteroaromatic ring of indole adsorbing CO₂via π–π-stacking interactions (a) and the CO₂ molecule is further stabled via the coefficient effect of π–π-stacking interactions and hydrogen bonding interactions (b). (c) Synthetic route of PIN-NH₂ aerogel.To verify our suppose, in this work, we tactfully designed and fabricated an aminated indole-based aerogel PIN-NH₂via Friedel–Crafts alkylation (Fig. 1c), and its CO₂ adsorption capacity and CO₂/CH₄ and CO₂/N₂ selectivity were immediately investigated. The successful preparation of PIN-NH₂ was confirmed by Fourier transform infrared spectroscopy (FT-IR) and ¹³C solid state cross-polarization magic-angle-spinning nuclear magnetic resonance (¹³C CP/MAS NMR) spectrometer, and the results are in good agreement with the proposed structures (Fig. S1 and S2, ESI^†). In the ¹³C CP/MAS NMR spectrum of PIN-NH₂, the peaks at 169–103 ppm are ascribed to the indole group carbons, and the signals located at 35–40 ppm are assigned to the methylene carbons (Fig. S1, ESI^†). For FT-IR spectrum (Fig. S2, ESI^†), the peak at 3438 cm⁻¹ is attributed to the stretching vibrations of N–H in amine unit and indole amine. The peaks at 2999 cm⁻¹ and 2927 cm⁻¹ are assigned to the stretching vibration of –CH₂– in the polymer network and the peaks at 1630 cm⁻¹ and 1480 cm⁻¹ are ascribed to the vibrations of the aromatic ring skeleton.The porosity of PIN-NH₂ was quantified by scanning electron microscopy (SEM), high-resolution transmission electron microscopy (TEM) and N₂ adsorption–desorption isotherms at 77 K. As shown in Fig. 2a, the SEM image displays that the PIN-NH₂ consists of aggregated particles with sub-micrometer sizes. And the microporous characteristic can be observed clearly from the TEM image as shown in Fig. 2b, the presence of porous structure provides the essential condition for CO₂ capture and separation. As shown in Fig. 2c, at a low pressure (0–0.1 bar), there is a rapid raise in the N₂ adsorption–desorption isotherm, indicating its microporous nature, and the increase in the N₂ sorption at a relatively high pressure (∼0.9 bar) shows the presence of meso- and macrostructures of the PIN-NH₂. The specific surface area calculated in the relative pressure (P/P₀) range from 0.01 to 0.1 shows that the Brunauer–Emmett–Teller (BET) specific surface area of PIN-NH₂ is up to 480 m² g⁻¹. Additionally, the pore-size distribution (PSD)²⁰ calculation result was shown in Fig. 2d and S3 ESI,^† which indicating the pore diameter is about 14 Å and further confirming the microporous feature of the PIN-NH₂. To gain further insight into the microstructural information, the powder wide-angle X-ray diffraction (PXRD) was further performed on the PIN-NH₂ polymer. As shown in Fig. S4, ESI,^† only a broad peak at 17.8° 2θ in the PXRD pattern is present, which clearly suggests that the polymer is mainly amorphous in nature. Additional, the thermogravimetric analysis (TGA) show that the microporous material is stable up to 370 °C indicating its potential in post combustion processes operated at high temperatures (Fig. S5, ESI^†).Open in a separate windowFig. 2The microstructures of PIN-NH₂ framework. (a) SEM, (b) TEM, (c) the nitrogen adsorption–desorption isotherms and (d) the pore size distribution of PIN-NH₂ framework.Owing to the artful structure design and particular preparation method, there is a reserved aniline group on the side of the indole group in the PIN-NH₂ network. It was expected that after the rapidly capture of the CO₂ molecule via the π–π-stacking interactions, the next aniline group would assist to further stabilize the CO₂ molecule via hydrogen bonding interactions, in other words, the coefficient effect of π–π-stacking interactions and hydrogen bonding interactions would make this porous organic polymer more efficiently attract CO₂ molecules, which inspires us to investigate the gas uptake capacity. Physisorption isotherms for CO₂ (at 273 K) measured with a pressure more than 1.0 bar indicated that the resulting PIN-NH₂ network exhibited a high carbon dioxide uptake of 27.7 wt% at 1.0 bar, as shown in Fig. 3a. Comparing with most of reported porous materials such as metal–organic frameworks,²¹ activated carbons,²² and microporous organic polymers,^23,24 the porous organic polymer PIN-NH₂ shows an enhanced CO₂ uptake (Table S1, ESI^†). The calculation of isosteric heat of adsorption of PIN-NH₂ shows that the heat of adsorption is 35.7 kJ mol⁻¹ (Fig. S6, ESI^†), which is higher than that of the reported azo-linked polymers (27.9–29.6 kJ mol⁻¹),²⁵ the acid-functionalized porous polymers (32.6 kJ mol⁻¹).^26,27 and the indole-based porous polymers.^28,29 The high value of the heat of adsorption indicated the strong physisorption effect owing to the coefficient effect of π–π-stacking interactions and hydrogen bonding interactions.Open in a separate windowFig. 3Gas adsorption isotherms of PIN-NH₂ for CO₂ at 273 K (a), adsorption and desorption isotherms of PIN-NH₂ for different gases at 273 K (b), a CO₂ molecule is adsorbed on the heteroaromatic ring of indole via π–π-stacking interaction (c) and the CO₂ molecule is further stabled via the coefficient effect of π–π-stacking and hydrogen bonding interactions (d), adsorption isotherms of PIN-NH₂ for different gases with 3% RH of water at 273 K (e), reversibility of the PIN-NH₂ polymer in CO₂ capture measured by TGA at 273 K (f).The application in CO₂ separation and adsorption field of the traditional POPs is limited in a great degree by the poor gas selectivity as the flue gas and natural gas are both mixed gas. Here, we believed that the CO₂ can be easily attracted by the heteroaromatic ring via the π–π-stacking interactions and then stabled with the assist of hydrogen bonding interactions, which leading an enhanced gas selectivity. Therefore, we urgently evaluated the selective gas uptake of the PIN-NH₂ network for small gases (CO₂/CH₄, CO₂/N₂). In the calculation, the ratio of CO₂/N₂ is 15/85 and the ratio of CO₂/CH₄ is 5/95, which is the typical composition of flue gas and natural gas, respectively, the test results were shown in Fig. 3b. It can be found there is a rapid increase for the CO₂ uptake while there is a negligible increase for the CH₄ and N₂ uptake with the increase of the pressure, which maybe due to the unique local dipole–π interactions between the porous organic framework PIN-NH₂ and CO₂ molecule. The test results shows that the CO₂ uptake of PIN-NH₂ is up to 5.92 mmol g⁻¹ at a pressure of 1.0 bar and a temperature of 273 K while the CH₄ and N₂ uptake of PIN-NH₂ is only 0.18 and 0.04 mmol g⁻¹, respectively. The estimated ideal CO₂/CH₄ and CO₂/N₂ adsorption selectivities are up to 34 and 137, respectively. Additionally, the selectivities of PIN-NH₂ toward CO₂ over CH₄ and N₂ at 291 and 303 K were also investigated, respectively, and the results indicated that the resulting polymer PIN-NH₂ still exhibited good selectivity at higher temperatures (Fig. S7 and S8, ESI^†).The high gas selectivities of this microporous framework may attribute to the strong affinity for CO₂ compared with N₂ and CH₄ arising from the coefficient effect of π–π-stacking interactions and hydrogen bonding interactions between the sorbent and CO₂ guest molecule, to further attest the above surmise, we used density functional theory (DFT)³⁰ at the M06-2X level with the aug-cc-pVDZ basis set to investigate the interaction of aminated indole system with CO₂ and the details of the calculation is shown in the ESI.^†Fig. 3c and d shows the snapshot for CO₂ capture by a model compound. The calculation result shows that owing to the electron-rich and large binding area, the CO₂ was very easily attracted by the indole plane at a distance of 3.706 Å, and the computational binding energy was 13.23 kJ mol⁻¹ (Fig. 3c). Soon, the balance structure was changed, the CO₂ molecular was moved towards the amino group till the distance between the amino group and CO₂ molecular was 3.037 Å, indicating a hydrogen bonding interaction was formed in this system. As a result, the distance between the indole plane and CO₂ molecular decreased to 3.257 Å from 3.706 Å, and the computational binding energy increased to 42.15 kJ mol⁻¹, which meaning a more steady system was formed (Fig. 3d). In the sense of computational chemistry, the expected strong coefficient effect of π–π-stacking interactions and hydrogen bonding interactions would favor the uptake of CO₂ of the PIN-NH₂ network. Additional, The DFT result also indicated that the interaction energy between CO₂ and the imine group of indole is relatively weak with a correlation distance at 4.041 Å.As we all know that the CO₂ adsorption property will be affected in a great degree for porous polymers in the presence of water.³¹ In real industrial applications, the flue gas from a power plant is a mixture of CO₂, water vapor, and others. As a result, it has very important practical significance to study the CO₂ capture performance under humid condition. Here, the CO₂ capture property of PIN-NH₂ was studied at a relative humidity of 3% RH, as shown in Fig. 3e, the CO₂ adsorption capacity of PIN-NH₂ decreased from 5.92 to 4.88 mmol g⁻¹ (1.0 bar, 273 K), however, the uptake of CH₄ and N₂ does not affected by the water. These results indicate that adsorption of water diminishes the CO₂ capture. Although the selectivity (CO₂/N₂ = 104, CO₂/CH₄ = 21) is decreased under humid condition, PIN-NH₂, to the best of our knowledge, still has very good CO₂ selectivity over other CO₂ capture materials in similar conditions.³² Moreover, the CO₂ adsorption process is fully reversible (Fig. 3f). Herein, the new aminated indole-based aromatic porous organic polymer PIN-NH₂ synthesized from easily available starting materials demonstrated not only remarkable CO₂ capture capacity, but also prominent CO₂/N₂ and CO₂/CH₄ selectivities. Further, the dynamic breakthrough separation experiments of gas mixture at 298 K using a fixed-bed column packed with PIN-NH₂ was carried out to evaluate the performances of PIN-NH₂ aerogel in an actual adsorption-based separation process. The details of the experiment process were described in ESI.^† As shown in Fig. S9 and S10, ESI,^† the CH₄ and N₂ penetrated through the bed firstly with a retention time for only 6.5 and 3.4 min, respectively, while PIN-NH₂ column can retain CO₂ until above 23 min, which means the high CO₂ adsorption capacity and selectivity of the PIN-NH₂ adsorbent in actual application.     

Theoretical study of D–A′–π–A/D–π–A′–π–A triphenylamine and quinoline derivatives as sensitizers for dye-sensitized solar cells

We have designed four dyes based on D–A′–π–A/D–π–A′–π–A triphenylamine and quinoline derivatives for dye-sensitized solar cells (DSSCs) and studied their optoelectronic properties as well as the effects of the introduction of alkoxy groups and thiophene group on these properties. The geometries, single point energy, charge population, electrostatic potential (ESP) distribution, dipole moments, frontier molecular orbitals (FMOs) and HOMO–LUMO energy gaps of the dyes were discussed to study the electronic properties of dyes based on density functional theory (DFT). And the absorption spectra, light harvesting efficiency (LHE), hole–electron distribution, charge transfer amount from HOMO to LUMO (Q_CT), D index, H_CT index, S_m index and exciton binding energy (E_coul) were discussed to investigate the optical and charge-transfer properties of dyes by time-dependent density functional theory (TD-DFT). The calculated results show that all the dyes follow the energy level matching principle and have broadened absorption bands at visible region. Besides, the introduction of alkoxy groups into triarylamine donors and thiophene groups into conjugated bridges can obviously improve the stability and optoelectronic properties of dyes. It is shown that the dye D4, which has had alkoxy groups as well as thiophene groups introduced and possesses a D–π–A′–π–A configuration, has the optimal optoelectronic properties and can be used as an ideal dye sensitizer.

We have designed four dyes based on D–A′–π–A/D–π–A′–π–A triphenylamine and quinoline derivatives for DSSCs and studied their optoelectronic properties as well as the effects of the introduction of alkoxy groups and thiophene group on the properties.     

A porous organic polymer nanosphere-based fluorescent biosensing platform for simultaneous detection of multiplexed DNA via electrostatic attraction and π–π stacking interactions

One key challenge in oligonucleotide sequence sensing is to achieve multiplexed DNA detection in one sensor. Herein, a simple and efficient fluorescent biosensing platform is constructed to simultaneously detect multiplexed DNA depending on porous organic polymer (POP) nanospheres. The developed sensor is based on the concept that the POP nanospheres can efficiently quench the fluorescence emission of dye-labeled single-stranded DNA (ssDNA). Fluorescence quenching is achieved by the non-covalent assembly of multiple probes on the surface of POP nanospheres through electrostatic attraction and π–π stacking interactions, in which the electrostatic attraction plays a more critical role than π–π stacking. The formed dsDNA could be released off the surface of POP via hybridizing with the target DNA. Consequently, the target DNA can be quickly detected by fluorescence recovery. The biosensor could sensitively and specifically identify three target DNAs in the range of 0.1 to 36 nM, and the lowest detection limits are 50 pM, 100 pM, and 50 pM, respectively. It is noteworthy that the proposed platform is successfully applied to detect DNA in human serum. We perceive that the proposed sensing system represents a simple and sensitive strategy towards simultaneous and multiplexed assays for DNA monitoring and early clinical diagnosis.

This communication reports a simple and efficient fluorescent biosensing platform to simultaneously detect multiplexed DNA depending on porous organic polymer (POP) nanospheres by electrostatic attraction and π–π stacking interaction.     

Bright red emission with high color purity from Eu(iii) complexes with π-conjugated polycyclic aromatic ligands and their sensing applications

Eu(iii) complexes emit red light with a high color purity and have consequently attracted attention for development toward display and physical sensing applications. The characteristic pure color emission originates from the intra-4f–4f transition, and the brightness strongly depends on the electronic and steric structures of organic ligands. A large π-conjugated ligand design with a large absorption coefficient has been actively studied for achieving bright emission. The π-conjugated Eu(iii) luminophores also provide oxygen and temperature sensing properties by controlling their excited state dynamics based on π-electron systems. A comprehensive understanding of the design strategy of large π-conjugated ligands is crucial for the further development of luminescent Eu(iii) complexes. In this review, we summarize the research progress on π-conjugated Eu(iii) luminophores exhibiting bright emission and their physical sensing applications.

In this review, we summarize the research progress on π-conjugated Eu(iii) luminophores exhibiting bright emission and their physical sensing applications.     

A ZnS@N-GQD nanocomposite as a highly effective and easily retrievable catalyst for the sonosynthesis of β-amino carbonyls

A three-component reaction of acetophenone, aromatic aldehydes, and aniline derivatives has been achieved in the presence of a ZnS@nitrogen graphene quantum dot (N-GQD) nanocomposite as a highly effective heterogeneous catalyst to produce β-amino carbonyls. The catalyst has been characterized by XRD, SEM, TEM, FT-IR spectroscopy, EDS, BET and TGA techniques. The feasibility of carrying out the one-pot synthesis under ultrasonic irradiation with a heterogeneous nanocatalyst could improve the reaction rates and shorten the reaction times.

A flexible and highly efficient protocol for the sonosynthesis of β-amino carbonyls using a ZnS@N-GQD nanocomposite has been developed.     

Impact of various heterocyclic π-linkers and their substitution position on the opto-electronic attributes of the A–π–D–π–A type IECIO-4F molecule: a comparative analysis

To investigate the consequence of different substitution positions of various π-linkers on the photovoltaic properties of an organic solar cell molecule, we have introduced two series of six three-donor molecules, by the substitution of some effective π-linkers on the A–π–D–π–A type reference molecule IECIO-4F (taken as IOR). In series “a” the thienyl or furyl bridge is directly linked between the donor and acceptor moieties, while in series “b” the phenyl ring of the same bridge is working as the direct point of attachment. The frontier molecular orbitals, density of states, transition density matrix, molecular electrostatic potential surfaces, exciton binding energy, excitation energy, wavelength of maximum absorption, open-circuit voltage, fill factor, and some other photovoltaic attributes of the proposed molecules were analyzed through density functional theory (DFT) and its time-dependent (TD) approach; the TD-DFT method. Though both series of newly derived molecules were a step up from the reference molecule in almost all of the studied characteristics, the “a” series (IO1_a to IO3_a) seemed to be better due to their desirable properties such as the highest maximum absorption wavelength (λ_max), open-circuit voltage, and fill factor, along with the lowest excitation and exciton dissociation energy, etc. of its molecules. Also, the studied morphology, optical characteristics, and electronic attributes of this series of proposed molecules signified the fact that the molecules with thienyl or furyl ring working as the direct link between the acceptor and donor molecules showed enhanced charge transfer abilities, and could provide a maximum quantum yield of the solar energy supplied.

We have introduced two series of six three-donor molecules, by the substitution of some effective π-linkers on the A–π–D–π–A type reference molecule IECIO-4F (taken as IOR) for efficient organic solar cells.     

Characterization and simulation study of organic solar cells based on donor–acceptor (D–π–A) molecular materials

In this study, the analysis of microelectronic and photonic structure in a one dimension program [AMPS-1D] has been successfully used to study organic solar cells. The program was used to optimize the performance of organic solar cells based on (carbazole-methylthiophene), benzothiadiazole and thiophene [(Cbz-Mth)-B-T]2 as electron donors, and [6,6]-phenyl-C₆₁-butyric acid methyl ester (PCBM) as an electron acceptor. The optoelectronic properties of these dyes were investigated by using the Density Functional Theory DFT/B3LYP/6-31G(d,p) method. We studied the influence of the variation of the thickness of the active layer, the temperature, and the density of the effective states of the electrons and the holes in the conduction and valence bands respectively on the performance of the solar cells based on [(Cbz-Mth)-BT]2–PCBM as a photoactive material, sandwiched between a transparent indium tin oxide (ITO) and an aluminum (Al) electrode. The addition of other thiophene units in the copolymer or the deposition of a layer of PEDOT between the anode (ITO) and the active layer, improves the performances of the cell, especially resulting in a remarkable increase in the value of the power conversion efficiency (PCE).

The solar cell ITO/PEDOT/[(Cbz-Mth)-B-DT]2-A:PCBM/Al under study and the results obtained, including a power conversion efficiency of 11%. The impact of several parameters on the performance has been studied to obtain the optimal device architecture.     

Investigating ultrafast carrier dynamics in perovskite solar cells with an extended π-conjugated polymeric diketopyrrolopyrrole layer for hole transportation

Here, we show a new diketopyrrole based polymeric hole-transport material (PBDTP-DTDPP, (poly[[2,5-bis(2-hexyldecyl)-2,3,5,6-tetrahydro-3,6-dioxopyrrolo[3,4-c]pyrrole-1,4-diyl]-alt-[[2,2′-(4,8-bis(4-ethylhexyl-1-phenyl)-benzo[1,2-b:4,5-b′]dithiophene)bis-thieno[3,2-b]thiophen]-5,5′-diyl]])) for application in perovskite solar cells. The material performance was tested in a solar cell with an optimized configuration, FTO/SnO₂/perovskite/PBDTP-DTDPP/Au, and the device showed a power conversion efficiency of 14.78%. The device charge carrier dynamics were investigated using transient absorption spectroscopy. The charge separation and recombination kinetics were determined in a device with PBDTP-DTDPP and the obtained results were compared to a reference device. We find that PBDTP-DTDPP enables similar charge separation time (<∼4.8 ps) to the spiro-OMeTAD but the amount of nongeminate recombination is different. Specifically, we find that the polymeric PBDTP-DTDPP hole-transport layer (HTL) slows-down the second-order recombination much less than spiro-OMeTAD. This effect is of particular importance in studying the charge transportation in optimized solar cell devices with diketopyrrole based HTL materials.

Diketopyrrole based hole-transport organic semiconductor was employed in perovskite solar cells and charge carrier dynamics was explained.     

Mechanofluorochromism of (D–π–)2A-type azine-based fluorescent dyes

Bathochromic or hypsochromic shift-type mechanofluorochromism (b-MFC or h-MFC) was found for (D–π–)₂A-type azine-based fluorescent dyes OUY-2, OUK-2, and OUJ-2 possessing intramolecular charge-transfer (ICT) characteristics from two (diphenylamino)carbazole–thiophene units as D (electron-donating group)–π (π-conjugated bridge) moieties to a pyridine, pyrazine, or triazine ring as A (electron-withdrawing group): grinding of the recrystallized dyes induced red or blue shifts of the fluorescent colors, that is, bathochromic or hypsochromic shifts of the fluorescence maximum wavelengths (λ^fl-solid_max). The degrees of MFC evaluated by the absolute value of differences (Δλ^fl-solid_max) in λ^fl-solid_max before and after grinding of the recrystallized dyes increased in the order of OUY-2 (+7 nm) < OUK-2 (−17 nm) < OUJ-2 (+45 nm), so that OUJ-2 exhibits obvious b-MFC, but OUK-2 exhibits h-MFC. X-ray powder diffraction (XRD) and differential scanning calorimetry (DSC) demonstrated that the recrystallized dyes were in the crystalline state but the ground dyes were in the amorphous state. When the ground solids were heated above their crystallization temperatures (T_c), the colors and fluorescent colors recovered to the original ones before grinding or converted to other ones, that is, heating the ground solids in the amorphous state induced the recrystallization to recover the original microcrystals or to form other microcrystals due to polymorph transformation. However, (D–π–)₂Ph-type fluorescent dye OTK-2 having a phenyl group as a substitute for the azine rings exhibited non-obvious MFC. Molecular orbital (MO) calculations indicated that the values of the dipole moments (μ_g) in the ground state were 4.0 debye, 1.4 debye, 3.2 debye, and 2.9 debye for OTK-2, OUY-2, OUK-2, and OUJ-2, respectively. Consequently, on the basis of experimental results and MO calculations, we have demonstrated that the MFC of the (D–π–)₂A-type azine-based fluorescent dyes is attributed to reversible switching between the crystalline state of the recrystallized dyes and the amorphous state of the ground dyes with changes in the intermolecular dipole–dipole and π–π interactions before and after grinding. Moreover, this work reveals that (D–π–)₂A fluorescent dyes possessing dipole moments of ca. 3 debye as well as moderate or intense ICT characteristics make it possible to activate the MFC.

Bathochromic or hypsochromic shift-type mechanofluorochromism (b-MFC of h-MFC) was found for (D–π–)₂A-type azine-based fluorescent dyes: grinding of the recrystallized dyes induced bathochromic or hypsochromic shifts of the fluorescence bands.     

A novel indole-based conjugated microporous polymer for highly effective removal of heavy metals from aqueous solution via double cation–π interactions

A novel indole-based conjugated microporous polymer (PTIA) with three coplanar indole units, designed and synthesized by an oxidative coupling reaction, was utilized as a platform for removing heavy metals. Owing to the conjugation of the three coplanar indoles, the highly electron-rich large π planes can simultaneously attract six heavy metal atoms via double cation–π interactions, endowing this microporous material with remarkable heavy metal adsorption capacity and efficiency.

A novel indole-based conjugated microporous polymer (PTIA) with three coplanar indole units, designed and synthesized by an oxidative coupling reaction, was utilized as a platform for removing heavy metals.     

D–π–A azine based AIEgen with solvent dependent response towards a nerve agent

We developed a D–π–A based unsymmetrical azine molecule 4-((E)-((E)-(4-(dipropylamino)benzylidene)hydrazono)methyl)benzonitrile [DPBN] and studied its optical and aggregation induced emission properties. The DPBN molecule shows good aggregation induced emission (AIE) behaviour with 1157-fold fluorescence enhancement in the aggregated state. In addition to that, both colorimetric as well as fluorometric sensing studies revealed that DPBN selectively detects diethylchlorophosphate (DCP), a potent nerve agent. Interestingly, DPBN shows solvent dependent optical output in the presence of DCPvia two different mechanisms. In the monomer state, it shows red shifted fluorescence enhancement along with color change from colorless to orange color via the formation of a new intramolecular charge transfer state in pure tetrahydrofuran (THF). In the aggregated state, DPBN shows blue shifted emission with fluorescence enhancement in THF–water mixture by protonation at the amine nitrogen centre. Thus, DPBN can be used as a diagnostic measure to selectively detect nerve agents like DCP. This study also paves the way for further development of molecular probes for nerve agents that would represent immense implications in various fields of chemistry and biology.

Selective detection of diethylchlorophosphate using a D–π–A based AIEgen in aqueous as well as non-aqueous environment via different sensing mechanisms.     

Crystallization,rheology and mechanical properties of the blends of poly(l-lactide) with supramolecular polymers based on poly(d-lactide)–poly(ε-caprolactone-co-δ-valerolactone)–poly(d-lactide) triblock copolymers

In this study, we investigated the blending of poly(l-lactide) (PLLA) with supramolecular polymers based on poly(d-lactide)–poly(ε-caprolactone-co-δ-valerolactone)–poly(d-lactide) (PDLA–PCVL–PDLA) triblock copolymers as an efficient way to modify PLLA. The supramolecular polymers (SMP) were synthesized by the terminal functionalization of the PDLA–PCVL–PDLA copolymers with 2-ureido-4[1H]-pyrimidinone (UPy). The structure, thermal properties and rheological behavior of the synthesized supramolecular polymers were studied; we found that the formation of the UPy dimers expanded the molecular chain of the polymer and the incorporation of the UPy groups suppressed the crystallization of polymers. In addition, the synthesized supramolecular polymers had a low glass transition temperature of about −50 °C, showing the characteristics of elastomers. On this basis, superior properties such as a fast crystallization rate, high melt strength, and toughness of fully bio-based, i.e., PLA-based materials were achieved simultaneously by blending PLLA with the synthesized supramolecular polymers. In the PLLA/SMP blends, PLLA could form a stereocomplex with its enantiomeric PDLA blocks of supramolecular polymers, and the stereocomplex crystals with the cross-linking networks reinforced the melt strength of the PLLA/SMP blends. The influences of the SMP composition and the SMP content in the PLLA matrix on crystallization and mechanical properties were analyzed. The supramolecular polymers SMP0.49 and SMP1.04 showed a reverse effect on the crystallization of PLLA. Tensile tests revealed that the lower content of the synthesized supramolecular polymers could achieve toughening of the PLLA matrix. Therefore, the introduction of supramolecular polymers based on PDLA–PCVL–PDLA is an effective way to control the crystallization, rheology and mechanical properties of PLLA.

Supramolecular polymer based on PDLA–PCVL–PDLA triblock copolymer was used for the modification of PLLA, and the results showed that it is an effective way to control the crystallization, rheology and mechanical properties of PLLA.     

A novel and fast method to prepare a Cu-supported α-Sb2S3@CuSbS2 binder-free electrode for sodium-ion batteries

Antimony sulfide (Sb₂S₃) is a promising anode material for sodium-ion batteries due to its low cost and high theoretical specific capacity. However, poor stability and a complex preparation process limit its large-scale application. Herein, we prepare a binder-free composite electrode composed of amorphous (α-) Sb₂S₃ and copper antimony sulfide (CuSbS₂) through a simple closed-space sublimation (CSS) method. When applied as the anode in sodium-ion batteries, the α-Sb₂S₃@CuSbS₂ electrode exhibits excellent performance with a high discharge capacity of 506.7 mA h g⁻¹ at a current density of 50 mA g⁻¹ after 50 cycles. The satisfactory electrochemical performance could be ascribed to the α-Sb₂S₃–CuSbS₂ composite structure and binder-free electrode architecture, which not only retain the structural stability of the electrode but also improve the electrical conductivity. Consequently, CSS, as a scalable and environmentally friendly method, can produce a binder-free electrode in just a few minutes, demonstrating its great potential in the industrial production of sodium-ion batteries. This study may open an avenue to preparing binder-free commercial electrodes.

Antimony sulfide (Sb₂S₃) is a promising anode material for sodium-ion batteries due to its low cost and high theoretical specific capacity.     

Behaviour of the XH-*-π and YX-*-π interactions (X,Y = F,Cl, Br and I) in the coronene π-system,as elucidated by QTAIM dual functional analysis with QC calculations

The dynamic and static nature of XH-*-π and YX-*-π in the coronene π-system (π(C₂₄H₁₂)) is elucidated by QTAIM dual functional analysis, where * emphasizes the presence of bond critical points (BCPs) in the interactions. The nature of the interactions is elucidated by analysing the plots of the total electron energy densities H_b(r_c) versus H_b(r_c) − V_b(r_c)/2 [=(ħ²/8m)∇²ρ_b(r_c)] for the interactions at BCPs, where V_b(r_c) are the potential energy densities at the BCPs. The data for the perturbed structures around the fully optimized structures are employed for the plots in addition to those of the fully optimized structures. The plots are analysed using the polar coordinate of (R, θ) for the data of the fully optimized structures, while those containing the perturbed structures are analysed using (θ_p, κ_p), where θ_p corresponds to the tangent line of each plot and κ_p is the curvature. Whereas (R, θ) show the static nature, (θ_p, κ_p) represent the dynamic nature of the interactions. All interactions in X–H-*-π(C₂₄H₁₂) (X = F, Cl, Br and I) and Y–X-*-π(C₂₄H₁₂) (Y–X = F–F, Cl–Cl, Br–Br, I–I, F–Cl, F–Br and F–I) are classified by pure CS (closed shell) interactions and are characterized as having the vdW nature, except for X–H = F–H and Y–X = F–Cl, F–Br and F–I, which show the typical-HB nature without covalency. The structural features of the complexes are also discussed.

The XH-*-π(C₂₄H₁₂) interactions appear on the outside ring of C₂₄H₁₂, while YX-*-π(C₂₄H₁₂) do both on the inside and outside rings.     

First principles study of electronic and nonlinear optical properties of A–D–π–A and D–A–D–π–A configured compounds containing novel quinoline–carbazole derivatives

Materials with nonlinear optical (NLO) properties have significant applications in different fields, including nuclear science, biophysics, medicine, chemical dynamics, solid physics, materials science and surface interface applications. Quinoline and carbazole, owing to their electron-deficient and electron-rich character respectively, play a role in charge transfer applications in optoelectronics. Therefore, an attempt has been made herein to explore quinoline–carbazole based novel materials with highly nonlinear optical properties. Structural tailoring has been made at the donor and acceptor units of two recently synthesized quinoline–carbazole molecules (Q1, Q2) and acceptor–donor–π–acceptor (A–D–π–A) and donor–acceptor–donor–π–acceptor (D–A–D–π–A) type novel molecules Q1D1–Q1D3 and Q2D2–Q2D3 have been quantum chemically designed, respectively. Density functional theory (DFT) and time-dependent density functional theory (TDDFT) computations are performed to process the impact of acceptor and donor units on photophysical, electronic and NLO properties of selected molecules. The λ_max values (321 and 319 nm) for Q1 and Q2 in DSMO were in good agreement with the experimental values (326 and 323 nm). The largest shift in absorption maximum is displayed by Q1D2 (436 nm). The designed compounds (Q1D3–Q2D3) express absorption spectra with an increased border and with a reduced band gap compared to the parent compounds (Q1 and Q2). Natural bond orbital (NBO) investigations showed that the extended hyper conjugation and strong intramolecular interaction play significant roles in stabilising these systems. All molecules expressed significant NLO responses. A large value of β_tot was elevated in Q1D2 (23 885.90 a.u.). This theoretical framework reveals the NLO response properties of novel quinoline–carbazole derivatives that can be significant for their use in advanced applications.

Materials with nonlinear optical properties have significant applications in nuclear science, biophysics, medicine, chemical dynamics, solid physics & materials science. We show how π bridges, donors & acceptors can be reconfigured to improve optical properties.