Regio-regular alternating diketopyrrolopyrrole-based D1–A–D2–A terpolymers for the enhanced performance of polymer solar cells

We designed and synthesized regio-regular alternating diketopyrrolopyrrole (DPP)-based D₁–A–D₂–A terpolymers (PDPPF2T2DPP-T2, PDPPF2T2DPP-TVT, and PDPPF2T2DPP-DTT) using a primary donor (D₁) [3,3′-difluoro-2,2′-bithiophene (F2T2)] and a secondary donor (D₂) [2,2′-bithiophene (T2), (E)-1,2-di(thiophen-2-yl)ethene (TVT), or dithieno[3,2-b:2′,3′-d]thiophene (DTT)]. A PDPP2DT-F2T2 D–A polymer was synthesized as well to compare optical, electronic, and photovoltaic properties. The absorption peaks of the terpolymers (PDPPF2T2DPP-T2, PDPPF2T2DPP-TVT, and PDPPF2T2DPP-DTT) were longer (λ_max = 801–810 nm) than the peak of the PDPP2DT-F2T2 polymer (λ_max = 799 nm), which is associated with the high-lying HOMO levels of the terpolymers (−5.08 to −5.13 eV) compared with the level of the PDPP2DT-F2T2 polymer (−5.38 eV). The photovoltaic properties of these DPP-based polymers were investigated under simulated AM 1.5G sunlight (100 mW cm⁻²) with a conventional structure (ITO/PEDOT:PSS/polymer:PC₇₁BM/Al). The open-circuit voltages (V_oc) of photovoltaic devices containing the terpolymers were slightly lower (0.68–0.70 V) than the V_oc of the device containing the PDPP2DT-F2T2 polymer (0.79 V). The short-circuit current (J_sc) of the PDPPF2T2DPP-DTT device was significantly improved (14.14 mA cm⁻²) compared with that of the PDPP2DT-F2T2 device (8.29 mA cm⁻²). As a result, the power conversion efficiency (PCE) of the PDPPF2T2DPP-DTT device (6.35%) was increased by 33% compared with that of the simple D–A-type PDPP2DT-F2T2 device (4.78%). The highest J_sc and PCE values (the PDPPF2T2DPP-DTT device) were attributed to an optimal nanoscopically mixed morphology and strong interchain packing with a high face-on orientation in the blend film state. The study demonstrated that our strategy of using multiple donors in a regio-regular alternating fashion could fine-tune the optical, electronic, and morphological properties of D–A-type polymers, enhancing the performance of polymer solar cells.

We designed and synthesized regio-regular alternating diketopyrrolopyrrole (DPP)-based D₁–A–D₂–A terpolymers (PDPPF2T2DPP-T2, PDPPF2T2DPP-TVT, and PDPPF2T2DPP-DTT) for use in polymer solar cells.     

The impact of thermal treatment on the performance of benzo[1,2-b:4,5-b′]difuran-based organic solar cells

The new low bandgap benzo[1,2-b:4,5-b′]difuran (BDF)-based organic small molecule, namely B1, was synthesized by Stille coupling polymerization reactions. B1 was found to be soluble in common organic solvents such as chloroform, toluene and chlorobenzene with excellent film forming properties. The structure of B1 was verified by ¹H NMR, GC-MS and elemental analysis. The B1 films exhibit broad absorption bands from 300 to 750 nm. The hole mobility of B1 : PC₆₁BM (1 : 1, w/w) blend film reached up to 7.7 × 10⁻² cm V⁻¹ s⁻¹ after thermal annealing by the space-charge-limited current method. BHJ organic solar cells (OSCs) were fabricated with a device structure of ITO/PEDOT : PSS/B1 : C₆₁BM/LiF/Al. When the active layer was thermally annealed at 120 °C, B1 showed the best photovoltaic performance, with a PCE up to 5.0%. We also studied the connection between the morphologies of the active layers and the photovoltaic performance by AFM, PL, etc. Our observation will guide future design for even better small molecules for highly efficient OSCs.

The new low bandgap benzo[1,2-b:4,5-b′]difuran (BDF)-based organic small molecule, namely B1, was synthesized by Stille coupling polymerization reactions.     

Reactive molecular dynamics simulation of the high-temperature pyrolysis of 2,2′,2′′,4,4′,4′′,6,6′,6′′-nonanitro-1,1′:3′,1′′-terphenyl (NONA)

2,2′,2′′,4,4′,4′′,6,6′,6′′-Nonanitro-1,1′:3′,1′′-terphenyl (NONA) is currently recognized as an excellent heat-resistant explosive. To improve the atomistic understanding of the thermal decomposition paths of NONA, we performed a series of reactive force field (ReaxFF) molecular dynamics simulations under extreme conditions of temperature and pressure. The results show that two distinct initial decomposition mechanisms are the homolytic cleavage of the C–NO₂ bond and nitro–nitrite (NO₂ → ONO) isomerization followed by NO fission. Bimolecular and fused ring compounds are found in the subsequent decomposition of NONA. The product identification analysis under finite time steps showed that the gaseous products are CO₂, N₂, and H₂O. The amount of CO₂ is energetically more favorable for the system at high temperature or low density. The carbon-containing clusters are a favorable growth pathway at low temperatures, and this process was further demonstrated by the analysis of diffusion coefficients. The increase of the crystal density accelerates the decomposition of NONA judged by the analysis of reaction kinetic parameters and activation barriers. In the endothermic and exothermic stages, a 20% increase in NONA density increases the activation energies by 3.24 and 0.48 kcal mol⁻¹, respectively. The values of activation energies (49.34–49.82 kcal mol⁻¹) agree with the experimental data in the initial decomposition stage.

The bimolecular and fused ring compounds are found in the high-temperature pyrolysis of NONA using ReaxFF molecular dynamics simulations.     

[2,2′-Bithiophene]-4,4′-dicarboxamide: a novel building block for semiconducting polymers

A novel electron deficient building block [2,2′-bithiophene]-4,4′-dicarboxamide (BTDCA) was designed to lower the highest occupied molecular orbital (HOMO) energy level of polythiophenes in order to achieve a higher open circuit voltage (V_oc) and thus a higher power conversion efficiency in polymer solar cells (PSCs). BTDCA dibromo monomers were conveniently synthesized in four steps, and were used to prepare three thiophene-based D-A polymers, P(BTDCA66-BT) (66BT), P(BTDCA44-BT) (44BT) and P(BTDCA44-TT) (44TT). All the polymers exhibited unipolar hole transport properties, exhibiting mobilities in the range of ∼10⁻⁴ to 10⁻² cm² V⁻¹ s⁻¹ with the highest hole mobility of up to 1.43 × 10⁻² cm² V⁻¹ s⁻¹ achieved for 44BT in bottom-gate bottom-contact organic thin film transistors (OTFTs). In PSCs, these polymers achieved high V_oc''s of 0.81–0.87 V when PCBM or ITIC was used as acceptor. When 44TT was used as donor and ITIC was used as acceptor, a power conversion efficiency (PCE) of up to 4.5% was obtained, a significant improvement when compared with the poly(3-hexylthiophene) (P3HT):ITIC devices, which showed the highest PCE of merely 0.92%.

A new electron acceptor building block, [2,2′-bithiophene]-4,4′-dicarboxamide, is synthesized and used to develop donor polymers for organic solar cells.     

Organic binary charge-transfer compounds of 2,2′ : 6′,2′′ : 6′′,6-trioxotriphenylamine and a pyrene-annulated azaacene as donors

Three binary charge-transfer (CT) compounds resulting from the donor 2,2′ : 6′,2′′ : 6′′,6-trioxotriphenylamine (TOTA) and the acceptors F₄TCNQ and F₄BQ and of a pyrene-annulated azaacene (PAA) with the acceptor F₄TCNQ are reported. The identity of these CT compounds are confirmed by single-crystal X-ray diffraction as well as by IR, UV-vis-NIR and EPR spectroscopy. X-ray diffraction analysis reveals a 1 : 1 stoichiometry for TOTA·F₄TCNQ, a 2 : 1 donor : acceptor ratio in (TOTA)₂·F₄BQ, and a rare 4 : 1 stoichiometry in (PAA)₄·F₄TCNQ, respectively. Metrical parameters of the donor (D) and acceptor (A) constituents as well as IR spectra indicate full CT in TOTA·F₄TCNQ, partial CT in (TOTA)₂·F₄BQ and only a very modest one in (PAA)₄·F₄TCNQ. Intricate packing motifs are present in the crystal lattice with encaged, π-stacked (F₄TCNQ⁻)₂ dimers in TOTA·F₄TCNQ or mixed D/A stacks in the other two compounds. Their solid-state UV-vis-NIR spectra feature CT transitions. The CT compounds with F₄TCNQ are electrical insulators, while (TOTA)₂·F₄BQ is weakly conducting.

Three binary charge-transfer (CT) compounds resulting from the donor 2,2′ : 6′,2′′ : 6′′,6-trioxotriphenylamine (TOTA) and the acceptors F₄TCNQ and F₄BQ and of a pyrene-annulated azaacene (PAA) with the acceptor F₄TCNQ are reported.     

The synthesis of triazine–thiophene–thiophene conjugated porous polymers and their composites with carbon as anode materials in lithium-ion batteries

The polymers based on thiophene armed triazine and different thiophene derivatives including thiophene (Th), thieno[3,2-b]thiophene (TT), dithieno[3,2-b:2′,3′-d]thiophene (DTT) or thieno[2′,3'':4,5]thieno[3,2-b]thieno[2,3-d]thiophene (TTTT) are synthesized through a Stille coupling reaction. By introducing thiophene derivatives with increasing sizes as the linkage units (from thiophene, DT to DTT, TTTT), the band gaps (E_g) of the resultant polymers decrease continuously. Then the composite materials (polymer@C) between polymers and Vulcan XC-72 carbon are prepared by in situ polymerization to test their electrochemical performances in lithium ion batteries. The synthesized composites show distinct morphologies due to the different linkage units of thiophene or fused cyclothiophene derivatives and the cross-linked structure can be found in composites with the longer thiophene derivatives (bridging molecules) like PTT-3@C and PTT-4@C, which are expected to be beneficial to improve the performances of the electrode materials. The specific capacities of the composites are 495 mA h g⁻¹, 671 mA h g⁻¹, 707 mA h g⁻¹, and 772 mA h g⁻¹ for PTT-1@C, PTT-2@C, PTT-3@C and PTT-4@C at a current density of 100 mA g⁻¹, respectively. In particular, benefiting from the enlarged conjugation length and planarity of the linkage units, the conjugated microporous polymers could deliver continuously improved capacities.

Four different kinds of conjugated porous polymers PTTs were synthesized and their composites with carbon material were used as the electrode materials for LIBs.     

Tuning the performance of the non-fullerene organic solar cells by the polarizability

We report here the synthesis and characterizations of a novel series of acceptor copolymers with a broad absorption band. The acceptor polymers were synthesized as a copolymer of perylenediimide (PDI) and naphthalene imide (NDI) along with dithieno[3,2-b:2′,3′-d]silole (DTS) and N-alkyl dithieno[3,2-b:2′,3-d]pyrroles (DTP). When the dipole moment and polarizability of the acceptor polymer are compared, it is observed that when the dipole moment decreases, the polarizability becomes larger. The polarizability of polymers containing PDI is significantly greater than those containing NDI, and their polarizability change is in accordance with the change in the transient fluorescence lifetime. It was also found that the power conversion efficiency of the non-fullerene solar cell was strongly correlated to polarizability. The results demonstrate that the polarizability can be utilized to screen novel donor and acceptor polymers for the design and synthesis of high-performance solar cells.

The PCE of solar cells has a direct relationship with the polarizability is also directly related to the PL lifetime. The performance of non-fullerene solar cells can be controlled by polarizability.     

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.     

Hot exciton transition for organic light-emitting diodes: tailoring excited-state properties and electroluminescence performances of donor–spacer–acceptor molecules

The photophysical, electrochemical and electroluminescent properties of newly synthesized blue emitters with donor–π–acceptor geometry, namely, 4′-(1-(naphthalen-1-yl)-1H-phenanthro[9,10-d]imidazol-2-yl)-N,N-diphenyl-(2-[1,1′-biphenyl]vinyl)-4-amine (NSPI-TPA), 4′-(1-(2-methylnaphthalen-1-yl)-1H-phenanthro[9,10-d]imidazol-2-yl)-N,N-diphenyl-(2-[1,1′-biphenyl]vinyl)-4-amine (MNSPI-TPA), 4-(2-(4′-(diphenylamino)-(2-[1,1′-biphenyl]vinyl)-4-yl)-1H-phenanthro[9,10-d]imidazol-1-yl)-1-naphthalene-1-carbonitrile (SPNCN-TPA) and 4-(2-(4-(9H-carbazol-9-yl)styryl)-1H-phenanthro[9,10-d]imidazol-1-yl)naphthalene-1-carbonitrile (SPNCN-Cz) were analyzed. The conjugation length in the emitters is not conducive to pure emission and hence, a molecular twisting strategy was adopted in NSPI-TPA, MNSPI-TPA, SPNCN-TPA and SPNCN-Cz to enhance pure emission. The emissive state (HLCT) of twisted D–π–A molecules containing both LE and CT (HLCT) states was tuned for high PL (η_PL) (LE) and high exciton utilization (η_s) (CT) efficiencies by replacing triphenylamine (strong donor) with carbazole (weak donor). Among strong donor compounds, namely, NSPI-TPA, MNSPI-TPA and SPNCN-TPA, the SPNCN-TPA-based device exhibited blue emission (451 nm) with CIE coordinates (0.15, 0.08), maximum current efficiency (η_c) of 2.32 cd A⁻¹, power efficiency (η_p) of 2.01 lm W⁻¹ and external quantum efficiency (η_ex) of 3.02%. The device with SPNCN-Cz emitter exhibited higher electroluminescence efficiencies than the SPNCN-TPA-based device, with pure blue emission (443 nm, CIE: 0.15,0.07), η_ex of 3.15%, η_c of 2.56 cd A⁻¹ and η_p of 2.45 lm W⁻¹.

SPNCN-Cz device exhibits η_ex (3.15%), η_c (2.56 cd A⁻¹), η_p (2.45 lm W⁻¹) with CIE (0.15, 0.07).     

Vinylene and benzo[c][1,2,5]thiadiazole: effect of the π-spacer unit on the properties of bis(2-oxoindolin-3-ylidene)-benzodifuran-dione containing polymers for n-channel organic field-effect transistors

Two polymers based on (3E,7E)-3,7-bis(2-oxoindolin-3-ylidene)benzo[1,2-b:4,5-b′]difuran-2,6(3H,7H)-dione (BIBDF) coupled with (E)-2-(2-(thiophen-2-yl)vinyl)thiophene (TVT) or dithienylbenzothiadiazole (TBT), namely PBIBDF-TVT and PBIBDF-TBT were synthesized via the Stille coupling reaction. The effect of benzothiadiazole or vinylene-π spacer of the copolymers on optical properties, energy levels, electronic device performance and microstructure were studied. It was found that PBIBDF-TBT based OFET devices, annealed at 180 °C, showed better performance with the highest electron mobility of 2.9 × 10⁻² cm² V s⁻¹ whereas PBIBDF-TVT polymer exhibited 5.0 × 10⁻⁴ cm² V s⁻¹. The two orders of magnitude higher electron mobility of PBIBDF-TBT over PBIBDT-TVT is a clear indicator of the better charge transport ability of this polymer semiconductor arising from its higher crystallinity and better donor–acceptor interaction.

Bottom-gate-top-contact OFET device structure using PBIBDF-TVT and PBIBDF-TBT based polymer semiconductors.     

P-stereocontrolled synthesis of oligo(nucleoside N3′→O5′ phosphoramidothioate)s – opportunities and limitations

3′-N-(2-Thio-1,3,2-oxathiaphospholane) derivatives of 5′-O-DMT-3′-amino-2′,3′-dideoxy-ribonucleosides (_NOTP-N), that bear a 4,4-unsubstituted, 4,4-dimethyl, or 4,4-pentamethylene substituted oxathiaphospholane ring, were synthesized. Within these three series, _NOTP-N differed by canonical nucleobases (i.e., Ade^Bz, Cyt^Bz, Gua^iBu, or Thy). The monomers were chromatographically separated into P-diastereomers, which were further used to prepare N_NPSN′ dinucleotides (3), as well as short P-stereodefined oligo(deoxyribonucleoside N3′→O5′ phosphoramidothioate)s (NPS-) and chimeric NPS/PO- and NPS/PS-oligomers. The condensation reaction for _NOTP-N monomers was found to be 5–6 times slower than the analogous OTP derivatives. When the 5′-end nucleoside of a growing oligomer adopts a C3′-endo conformation, a conformational ‘clash’ with the incoming _NOTP-N monomer takes place, which is a main factor decreasing the repetitive yield of chain elongation. Although both isomers of N_NPSN′ were digested by the HINT1 phosphoramidase enzyme, the isomers hydrolyzed at a faster rate were tentatively assigned the R_P absolute configuration. This assignment is supported by X-ray analysis of the protected dinucleotide ^DMTdG^iBu_NPSMeT_OAc, which is P-stereoequivalent to the hydrolyzed faster P-diastereomer of dG_NPST.

Separated P-diastereomers of 3′-N-(2-thio-1,3,2-oxathiaphospholane) derivatives of 5′-O-DMT-3′-amino-2′,3′-dideoxy-ribonucleosides were used to prepare P-stereodefined N_NPSN′ dinucleotides and short NPS-, NPS/PO- and NPS/PS-oligomers.     

Synthesis,cytotoxicity evaluation and molecular docking studies on 2′,4′-dihydroxy-6′-methoxy-3′,5′-dimethylchalcone derivatives

2′,4′-Dihydroxy-6′-methoxy-3′,5′-dimethylchalcone (DMC, 1) was isolated from seeds of Syzygium nervosum A.Cunn. ex DC. exhibiting intriguing biological activities. Herein, thirty three DMC derivatives including 4′-O-monosubstituted-DMC (2), 7-O-acylated-4-hydroxycoumarin derivatives (3), stilbene–coumarin derivatives (4), 2′,4′-disubstituted-DMC (5), and flavanone derivatives (6), were synthesised through acylation, alkylations, and sulfonylation. These semi-synthetic DMC derivatives were evaluated for in vitro cytotoxicity against six carcinoma cell lines. It was found that most derivatives exhibited higher cytotoxicity than DMC. In particular, 4′-O-caproylated-DMC (2b) and 4′-O-methylated-DMC (2g) displayed the strongest cytotoxicity against SH-SY5Y with IC₅₀ values of 5.20 and 7.52 μM, respectively. Additionally, 4′-O-benzylated-DMC (2h) demonstrated the strongest cytotoxicity against A-549 and FaDu with IC₅₀ values of 9.99 and 13.98 μM, respectively. Our structure–activity relationship (SAR) highlights the importance of 2′-OH and the derivatisation pattern of 4′-OH. Furthermore, molecular docking simulation studies shed further light on how these bioactive compounds interact with cyclin-dependent kinase 2 (CDK2).

Semi-synthetic DMC derivatives were synthesised and displayed biological potency against various cancer cell lines.      

High-resolution X-ray diffraction determination of the electron density of 1-(8-PhSC10H6)SS(C10H6SPh-8′)-1′ with the QTAIM approach: evidence for S4 σ(4c–6e) at the naphthalene peri-positions

An extended hypervalent S₄ σ(4c–6e) system was confirmed for the linear ^BS-∗-^AS-∗-^AS-∗-^BS interaction in 1-(8-Ph^BSC₁₀H₆)^AS–^AS(C₁₀H₆^BSPh-8′)-1′ (1) via high-resolution X-ray diffraction determination of electron densities. The presence of bond critical points (BCPs; ∗) on the bond paths confirms the nature and extent of this interaction. The recently developed QTAIM dual functional analysis (QTAIM-DFA) approach was also applied to elucidate the nature of the interaction. Total electron energy densities H_b(r_c) were plotted versus H_b(r_c) − V_b(r_c)/2 for the interaction at the BCPs, where V_b(r_c) represents the potential energy densities at the BCP. The results indicate that although the data for an interaction in the fully optimized structure corresponds to a static nature, the data obtained for the perturbed structures around it represent the dynamic nature of the interaction in QTAIM-DFA. The former classifies the interaction and the latter characterises it. Although ^AS-∗-^AS in 1 is classified by a shared shell interaction and exhibits weak covalent character, ^AS-∗-^BS is characterized as having typical hydrogen-bond nature with covalent properties in the region of the regular closed shell interactions. The experimental results are supported by matching theoretical calculations throughout, particularly for the extended hypervalent E₄ σ(4c–6e) (E = S) interaction.

The nature of S₄ σ(4c–6e) at the 1,8-positions of naphthalene is elucidated via a high-resolution X-ray method with the QTAIM approach.     

Effect of fluorine substituents on benzothiadiazole-based D–π–A′–π–A photosensitizers for dye-sensitized solar cells

Two D–π–A′–π–A organic dyes with triazatruxene (TAT) as the electron donor, thiophene as the π-spacer, benzoic acid as the anchor group, and benzothiadiazole (BT) or difluorobenzo[c][1,2,5]thiadiazole (DFBT) as the additional acceptor, namely LS101 and LS102, respectively, were applied to dye-sensitized solar cells (DSSCs). As fluorine substituents are usually strong electron-withdrawing groups, introducing two fluorine atoms into BT was expected to strengthen the electron-withdrawing ability of the auxiliary acceptor, resulting in DSSCs with a broader light capture region and further improved power conversion efficiency (PCE). Fluorine is the smallest electron-withdrawing group with an induction effect, but can also act as an electron-donating group owing to its conjugation effect. When the conjugation effect is dominant, the electron-withdrawing ability of additional acceptor DFBT decreases instead. Accordingly, the band gap of LS102 was broadened and the UV-vis absorption spectrum was blue-shifted. In the end, DSSCs based on LS101 achieved a champion PCE of 10.2% (J_sc = 15.1 mA cm⁻², V_oc = 966 mV, FF = 70.1%) while that based on LS102 gave a PCE of only 8.6% (J_sc = 13.4 mA cm⁻², V_oc = 934 mV, FF = 69.1%) under standard AM 1.5G solar irradiation (100 mW cm⁻²) with Co²⁺/Co³⁺ as the electrolyte.

The results and interpretations can clearly explain the reasons for the poor photovoltaic performance of DFBT in DSSCs.     

Donor–acceptor duality of the transition-metal-like B2 core in core–shell-like metallo-borospherenes La3&[B2@B17]− and La3&[B2@B18]−

Transition-metal doping induces dramatic structural changes and leads to earlier planar → tubular → spherical → core–shell-like structural transitions in boron clusters. Inspired by the newly discovered spherical trihedral metallo-borospherene D_3h La₃&B₁₈⁻ (1) (Chen, et al., Nat. Commun., 2020, 11, 2766) and based on extensive first-principles theory calculations, we predict herein the first and smallest core–shell-like metallo-borospherenes C_2v La₃&[B₂@B₁₇]⁻ (2) and D_3h La₃&[B₂@B₁₈]⁻ (3) which contain a transition-metal-like B₂ core at the cage center with unique donor–acceptor duality in La₃&B_n⁻ spherical trihedral shells (n = 17, 18). Detailed energy decomposition and bonding analyses indicate that the B₂ core in these novel complexes serves as a π-donor in the equatorial direction mainly to coordinate three La atoms on the waist and a π/σ-acceptor in the axial direction mainly coordinated by two B₆ triangles on the top and bottom. These highly stable core–shell complexes appear to be spherically aromatic in nature in bonding patterns. The IR, Raman, and photoelectron spectra of 2 and 3 are computationally simulated to facilitate their spectroscopic characterizations.

The smallest core–shell-like metallo-borospherenes C_2v La3&[B₂@B₁₇]⁻ and D_3h La₃&[B₂@B₁₈]⁻ have been predicted at first-principles theory level which contain a transition-metal-like B₂ core with unique donor–acceptor duality.     

Polymers based on thieno[3,4-c]pyrrole-4,6-dione and pyromellitic diimide by CH–CH arylation reaction for high-performance thin-film transistors

Three homopolymers were successfully synthesized by direct CH–CH arylation polymerization of thieno[3,4-c]pyrrole-4,6-dione or pyromellitic diimide derivatives affording highly purified polymers with high molecular weights (43.0–174.7 K). Thieno[3,4-c]pyrrole-4,6-dione and pyromellitic diimide derivatives are considered as electron-withdrawing units. The synthesized homopolymers P1, P2, and P3 showed band gaps in the range of 2.13–2.08 eV, respectively. The electron mobilities of the three homopolymers have been investigated. The thin film transistor for P1 prepared by the eutectic-melt-assisted nanoimprinting method achieved an electron mobility of 2.11 × 10⁻³ cm² s⁻¹ V⁻¹. Based on the obtained results, the synthesized polymers can be used as potential electron acceptors in solar cell applications.

The homopolymers P1, P2 and P3 were successfully synthesized by direct CH–CH arylation polymerization in an eco-friendly one-step coupling reaction. They present n-type properties for potential applications as acceptor polymers.     

Efficient fluorescent OLEDS based on assistant acceptor modulated HLCT emissive state for enhancing singlet exciton utilization

Phenylamine phenanthroimidazole based bipolar compounds with donor–acceptor (D–A) architecture namely, 4-(1-(2,3-dihydrobenzo[b][1,4]dioxin-5-yl)-6,9-di(pyren-4-yl)-1H-phenanthro[9,10-d]imidazol-2-yl)-N,N-diphenylaniline (DDPPPA) and 4′-(1-(2,3-dihydrobenzo[b][1,4]dioxin-5-yl)-6,9-di(pyren-4-yl)-1H-phenanthro[9,10-d]imidazol-2-yl)-N,N-diphenyl-[1,1′-biphenyl]-4-amine (DDPBA) have been synthesized with highly fluorescent pyrene moieties at C6- and C9-positions. The C6 and C9 modification enhanced the thermal, photochemical and electroluminescent properties. Both molecules were employed as blue emitters in non doped organic light emitting devices (OLEDs) and show high performances due to hybridized local and charge-transfer properties. An OLED with DDPPPA/DDPBA emissive layer shows deep-blue emission with maximum external quantum efficiency (η_ex), current efficiency (η_c) and power efficiency (η_p) of 5.7/6.0%, 10.5/12.0 cd A⁻¹ and 8.3/9.2 lm W⁻¹, respectively. Both devices show high singlet exciton utilizing efficiency (η_s) of DDPPPA-31.33% and DDPBA-35.29%. The doped device m-MTDATA:DDPPPA/m-MTDATA:DDPBA shows maximum efficiencies of η_c −7.4/8.23 cd A⁻¹; η_p −5.8/6.13 lm W⁻¹; η_ex −4.72/5.63% (5 wt%):η_c −8.36/9.15 cd A⁻¹; η_p −6.32/6.65 lm W⁻¹; η_ex −4.86/5.45% (10 wt%):η_c −9.58/10.02 cd A⁻¹; η_p −7.8/8.25 lm W⁻¹; η_ex −5.96/6.25% (20 wt%). The doped device based on TAPC host TAPC:DDPPPA/TAPC:DDPBA exhibits maximum efficiencies of η_c −9.60/10.03 cd A⁻¹; η_p −7.81/8.26 lm W⁻¹; η_ex −5.96/6.25% (20 wt%).

OLED with C6/C9 substituted phenanthroimidazoles (DDPPPA/DDPBA) show blue emission with maximum external quantum efficiency (η_ex), current efficiency (η_c) and power efficiency (η_p) of 5.7/6.0%, 10.5/12.0 cd A⁻¹ and 8.3/9.2 lm W⁻¹, respectively.     

The modulation effect of pi–pi interactions on the electronic and photochromic properties of viologen complexes containing N,N′-bis(carboxyethyl)-4,4′-bipyridinium

Two viologen complexes containing N,N′-bis(carboxyethyl)-4,4′-bipyridinium (BCEbpy) were prepared, namely [Zn(H₂O)₆]·(BCEbpy)·(p-BDC)·3H₂O (1) and [Co(H₂O)₆]·(BCEbpy)·(p-BDC)·3H₂O (2) (p-H₂BDC = 1,4-benzenedicarboxylic acid), and their crystal structures, photochromism, frontier molecular orbitals, Hirshfeld surfaces and 2D fingerprint plots were investigated. The modulation effects of pi–pi interactions were explored on the electronic and photochromic properties of compounds 1 and 2. Due to the existence of photo-response viologen radicals, both complexes 1 and 2 display excellent photo-response properties in the sequence 1 < 2. The results indicate that compound 1 exhibits intramolecular electron transfer; compound 2 exhibits both intramolecular and intermolecular electron transfer, which is mainly due to the change of electronic and steric structures caused by pi–pi interactions with a faster photo-response rate than that of compound 1. The donor–acceptor modes, matching principles and inter/intramolecular atom–atom close contacts were illustrated by the density functional theory (DFT)-B3LYP/6-311(d,p) method.

Two viologen complexes containing BCEbpy were prepared and displayed excellent photo-response properties by the modulation effect of pi–pi interactions.     

Anti-inflammatory butenolide derivatives from the coral-derived fungus Aspergillus terreus and structure revisions of aspernolides D and G,butyrolactone VI and 4′,8′′-diacetoxy butyrolactone VI

Chemical investigation of the coral-derived fungus Aspergillus terreus led to the discovery of ten butenolide derivatives (1–10), including four new ones (1–4). The new structures were characterized on the basis of comprehensive spectroscopic analysis, including 1D and 2D NMR and HRESIMS data. Compounds 1 and 2 were a pair of rare C-8′′ epimers with vicinal diol motifs. The absolute configurations of 1–4 were determined via [Mo₂(AcO)₄] induced circular dichroism (ICD) spectra and comparison of their experimental ECD spectra. Importantly, the structures of reported aspernolides D and G, butyrolactone VI and 4′,8′′-diacetoxy butyrolactone VI have been correspondingly revised via a combined strategy of experimental validations, ¹³C NMR predictions by ACD/Labs software, and ¹³C NMR calculations. Herein we provide valuable referenced ¹³C NMR data (C-7′′, C-8′′, and C-9′′) for the structure elucidations of butenolide derivatives with 1-(2-hydroxyphenyl)-3-methylbutane-2,3-diol, 2-(2,3-dihydrobenzofuran-2-yl)propan-2-ol, or 2,2-dimethylchroman-3-ol motifs. Additionally, all the isolates (1–10) were assessed for anti-inflammatory activity by measuring the amount of NO production in lipopolysaccharide (LPS)-induced RAW 264.7 mouse macrophages, and compound 10 showed an even stronger inhibitory effect than the postive control indomethacin, presenting it as a promising lead compound for the development of new anti-inflammatory agents.

Chemical investigation of the coral-derived fungus Aspergillus terreus led to the discovery of ten butenolide derivatives (1–10), including four new ones (1–4).     

Interpretation of the mechanism of 3,3′-dichloro-4,4′-diamino diphenylmethane synthesis over HY zeolites

Catalytic activities of zeolites HY, Hβ and HZSM-5 in the heterogeneous synthesis of 3,3′-dichloro-4,4′-diaminodiphenyl methane (MOCA) from o-chloroaniline and formaldehyde were pre-screened in an autoclave, and HY demonstrated better performance than others. Kinetic behaviors of MOCA synthesis over HY(11) were further investigated in a fixed bed continuous flow reactor, and under the conditions of the catalyst bed volume = 20 mL (8.14 g), n(o-chloroaniline) : n(HCHO) = 4 : 1, LHSV = 3.5 h⁻¹, 0.5 MPa and 443 K, HCHO conversion and MOCA selectivity steadily fluctuated at high levels of 90–92% and 75–77% during 16 h, respectively. Catalysts were characterized by BET, NH₃-TPD and XRD, products analyzed by HPLC, and reaction intermediates identified by LC/MS and ¹H NMR. The mechanism of MOCA synthesis has been interpreted in detail, which also suggested that deposition of basic intermediates on active sites and accumulation of polymeric by-products in pore channels of the catalyst could cause significant decay of HY(11) activity and selectivity under severe conditions. Supplementary tests on catalyst regeneration confirmed that the acidity and surface area of spent HY(11) could be well recovered after burning off the deposited by-products.

Catalytic activities of zeolites HY, Hβ and HZSM-5 in the heterogeneous synthesis of 3,3′-dichloro-4,4′-diaminodiphenyl methane (MOCA) from o-chloroaniline and formaldehyde were pre-screened in an autoclave, and HY demonstrated better performance than others.