Second Order Nonlinear Optical Performances of Polymers Containing Imidazole and Benzimidazole Chromophores

Summary: Condensation polymers based on two different NLO‐active chromophores, namely 2‐[4‐[(4‐N,N‐dihydroxyethylamino)phenylazo]phenyl]‐5(6)‐nitrobenzimidazole (BZI) and 2‐[4‐(4‐N,N‐dihydroxyethylamino)phenylazo]‐4,5‐dicyanoimidazole (IMI), have been synthesized and their basic properties measured. The second order NLO properties of poled polymers were investigated by SHG procedures at different temperatures (35, 65 and 85 °C) and exposure times. Resonance free d₃₃ coefficients (λ = 1 368 nm) took values in the range 1.8–4.0 pm · V^?1, but the time stability of their SHG signal was fairly acceptable, particularly for the high T_g (e.g. 188 °C) polymer for which a relaxation time (at 25 °C) of 2.8 years has been determined.

BZI and IMI chromophores.     

Tailoring Linear and Nonlinear Optical Properties of a Side‐Chain Liquid Crystalline Azo‐Polymethacrylate

The molecular orientation in a side‐chain liquid crystalline azopolymer with push–pull chromophores ( Pol‐PZ‐CN ) is studied by UV‐vis spectroscopy, refractive index and second harmonic generation measurements. Fresh films show homeotropic arrangement, but irradiation with polarized light induces “in‐plane” birefringence, which is enhanced by subsequent thermal annealing up to values as high as 0.34. The nonlinear response of Corona poled films with “in‐plane” anisotropy is governed by three independent NLO d_ij coefficients, evidencing symmetry different from the usual (C_∞v). For irradiated films, stable values d₃₁ = 1.4, d₃₂ = 0.9 and d₃₃ = 11 pm·V^?1 are measured at 1.9 µm. A noticeable higher d₃₁/d₃₂ ratio is obtained for preirradiated and annealed films. The proposed two‐step method consisting of light irradiation and heating is an effective strategy to tailor the polar molecular orientation of nonlinear liquid crystalline azopolymers.

     

NLO Behavior of Polymers Containing Y‐Shaped Chromophores

New polyurethanes containing Y‐shaped chromophores, symmetrical derivatives of 4‐(dicyanomethylene)‐2‐methyl‐6‐[p‐(dimethylamino)styryl]‐4H‐pyran, have been prepared. The polymers show high glass transition temperatures (T_g) and a good thermal stability. SHG measurements on poled polymer films of the synthesized polymers have been carried out and a maximum d₃₃ of 15 pm · V^?1 has been found at 1 368 nm fundamental wavelength. Time stability measurements on the most active polymer have shown that after the initial fast relaxation, the d₃₃ value remains constant at 80 °C for 60 d.

     

Nonlinear Optical Properties and Liquid‐Crystalline Behavior of New Polyesters with Dipole Moments Aligned Transverse to the Backbone

Side‐chain azobenzene‐based second‐order nonlinear optical (NLO) polyesters ( PNPAR , PNPAPAR , PPAR‐TC , PPAPAR‐TC ) containing nitro or tricyanovinyl groups as acceptors with their dipole moments aligned transverse to the polymer backbone, were synthesized and characterized, and their thermal properties, liquid‐crystalline (LC) phase behavior, and NLO properties studied. Polymers containing nitro groups as acceptors were found to exhibit LC properties, while those containing tricyanovinyl groups as acceptors did not. The LC polymers were of smectic nature. The polymer PNPAR with a nitro group, when poled at the LC phase‐transition temperature range, was found to exhibit higher NLO activity than that with a tricyanovinyl group ( PPAR‐TC ). When polymer PNPAPAR containing a nitro group, also exhibiting an LC phase, was poled at a temperature different from that of its transition temperature, the NLO activity observed was comparable to, and/or lower than, that of the similar polymer ( PPAPAR‐TC ) having a tricyanobvinyl group in the place of the nitro group. All the polymers were found to possess moderate temporal stability of second harmonic generation activity and were found to have stability over the whole process.     

Benzo[1,2‐b:4,5‐b′]dithiophene‐alt‐terthiophene Copolymers Containing Styryl‐Triphenylamine Side Chains: Synthesis and Photovoltaic Performance Optimization with Fullerene Acceptors

A new two‐dimensional‐conjugated polymer (PBDTT3‐TPA) containing benzodithiophene (BDT) and a side chain isolation comonomer is designed and synthesized. Interestingly, PBDTT3‐TPA is compatible with higher lowest unoccupied molecular level (LUMO) acceptors of indene‐C₆₀ bisadduct (ICBA), and polymer solar cells based on PBDTT3‐TPA/ ICBA show an open‐circuit voltage (V_OC) of ca. 0.80 V and a power conversion efficiency of 2.48% under AM1.5G illumination of at 100 mW cm^?2. Furthermore, the energy loss in the corresponding fullerene acceptor devices is discussed, and the increase in the observed V_OC is explained quantitatively by the up‐shifted LUMO energy of ICBA (0.17 eV) and the reduced saturation current (J_SO) in the blends.

     

Temperature‐Responsive Water‐Soluble Copolymers Based on 2‐Hydroxyethyl Acrylate and Butyl Acrylate

Amphiphilic copolymers have been synthesised by free radical copolymerisation of 2‐hydroxyethyl acrylate with butyl acrylate, the reactivity ratios of which indicate practically equal reactivity. The copolymers containing less than 30 mol‐% of BA were soluble in water and exhibited a LCST in aqueous solutions. It was found that the interaction between these copolymers and poly(acrylic acid) in aqueous solutions resulted in the formation of interpolymer complexes stabilised by hydrogen bonds and hydrophobic interactions. This interaction was significantly affected by solution pH and led to modification of the temperature‐responsive behaviour of the copolymers.

     

Effects of Different Unsaturated‐Linker‐Containing Donors on Electronic Properties of Benzobisthiadiazole‐Based Copolymers

A series of new copolymers with unsaturated‐linker‐containing donors and benzobisthiadiazole acceptors are synthesized. Two kinds of side chains (2‐octyl‐1‐dodecyl chain and siloxane‐terminated hexyl chain) are added to the polymer backbone. The introduction of unsaturated‐linker‐containing donor enhances the rigidity of the copolymers. The strong electron‐withdrawing benzobisthiadiazole units make these copolymers display very narrow bandgaps in the range of 0.75–1.26 eV. Bottom‐gate and bottom‐contact transistors based on these polymers exhibit p‐type field‐effect behavior with hole mobilities up to 1.17 × 10^?3 cm² V^?1 s^?1.     

A New Approach Toward Metal‐Free Self‐Healing Ionomers Based on Phosphate and Methacrylate Containing Copolymers

In order to accelerate the progress of the development of new self‐healing ionomers, a new pathway toward fully organic ionomers containing methacrylic acid and phosphate‐based functional groups, respectively, as well as butyl methacrylate as comonomer is presented in the current study. The well‐defined copolymer structures are synthesized using the reversible addition‐fragmentation chain transfer polymerization and further characterized by NMR, size exclusion chromatography as well as titration. Two different metal‐free ionomers as well as one reference K⁺ based ionomer are created and tested. The results of the detailed investigation by NMR, thermal analysis, and rheology are correlated with the scratch‐healing performance in order to identify trends and dependencies leading to preconditions for further improvements.     

Atom Transfer Radical Polymerization and Third‐Order Nonlinear Optical Properties of New Azobenzene‐Containing Side‐Chain Polymers

The atom transfer radical polymerization (ATRP) technique has been successfully applied to synthesize a series of nonlinear optically (NLO) active homopolymers, 4‐(4‐nitrophenyl‐diazenyl) phenyl acrylate ( P ‐ NPAPA ) and 4‐(4‐methoxyphenyl‐diazenyl) phenyl acrylate ( P ‐ MPAPA ), containing azobenzene groups on the side chain. The third‐order NLO properties of the polymer films were measured by the degenerated four‐wave mixing (DFWM) technique. A dependence of the χ⁽³⁾ values and response times of polymers on their number‐average molecular weight and the electronic effect of the substituent (nitro‐ or methoxy‐) on the azobenzene group have been evidenced. The increasing χ⁽³⁾ value of the polymer films at the magnitude of about 10^?10 was displayed with increasing molecular weight and the presence of the push‐pull electronic system contributes much in enhancing the third‐order NLO susceptibility of polymers.

     

Sol–Gel Transitions of Comb‐Like Polymethacrylate Copolymers by Mechano‐Thermal Stimuli in Water

Sonogelation by supramolecular gelators is highlighted as a paradigm shift for their potential applications in material and biomedical sciences. Yet, these materials require organic solvents and low‐frequency ultrasound, limiting their utility. Here, a comb‐like polymethacrylate copolymer is synthesized with 2,6‐bis(1‐methylbenzimidazolyl)‐4‐oxypyridine tridentate ligand randomly distributed on poly(ethylene glycol) side chains. Upon addition of zinc perchlorate salt, this copolymer rapidly forms a hydrogel after exposure to either mechanical (i.e., ultrasound) or thermal stimuli. Spectroscopic analysis, to elucidate the mechanism, indicates metal ion coordination to ligand as well as the carbonyl and ethylene glycol units; interestingly, ¹H‐NMR suggests that the coordination between tridentate ligand moiety and Zn²⁺ is unexpectedly weaker in water than in acetonitrile. Investigations by dynamic light scattering indicates that the copolymer forms nanodispersions in excess salt, which coalesces to form a hydrogel by either heating or high intensity focused ultrasound (HIFU). Rheological quantification of these gels suggests stronger crosslinking by HIFU compared to heating.     

Self‐Assembly Behavior and Optical Properties of Poly(3‐thiopheneacetate)/Dialkyldimethylammonium Complexes

Poly(3‐thiopheneacetate)/dialkyldimethylammonium complexes (PTA‐Cn) were prepared by mixing regiorandom poly(3‐thiopheneacetic acid) with dialkyldimethylammonium bromide to study the effect of their self‐assembled structures on the optical properties. The lengths of the alkyl groups in the ammonium salts were varied from decyl (C10) to octadecyl (C18) groups. These complexes showed fully developed layer structures with ordered mesophases. PTA‐C16 and PTA‐C18 with longer alkyl groups showed side‐chain crystalline phases, and PTA‐C10, PTA‐C12, and PTA‐C14 with shorter alkyl groups showed side‐chain crystalline and liquid crystalline phases at room temperature. When PTA‐C18 was heated, a melting transition from side‐chain crystalline to smectic liquid crystalline phase was observed at 41.5 °C. The maximum absorption and emission wavelengths of these complexes increased with increasing alkyl chain length indicating that the π‐conjugated structure of the regiorandom thiophene backbone changes according to the alkyl groups.

     

Radical Copolymerization Reactivity of N‐Substituted Maleimides with α‐Substituted Styrenes with Various N‐ and α‐Substituents and the Thermal and Optical Properties of the Resulting Copolymers

The radical alternating copolymerization of N‐substituted maleimides (RMIs) with N‐methyl, n‐butyl, and 2‐ethylhexyl groups and styrene derivatives with various α‐substituents (RSs) is carried out. The yield and the molecular weight of the obtained copolymers significantly decrease with an increase in the size of the α‐substituent of RSs, but are independent of the N‐substituents. The glass‐transition temperature of the copolymers increases on the introduction of the large substituents into the RS repeating units. The high‐molecular‐weight poly(RMI‐alt‐RS)s are soluble in organic solvents and provide flexible and transparent films with excellent transparency by casting the solutions.

     

Amphiphilic Block Copolymers Containing Regioregular Poly(3‐hexylthiophene) and Poly(2‐ethyl‐2‐oxazoline)

Poly(3‐hexylthiophene)‐block‐poly(2‐ethyl‐2‐oxazoline) amphiphilic rod–coil diblock copolymers have been synthesized by a combination of Grignard metathesis (GRIM) and ring‐opening cationic polymerization. Diblock copolymers containing 5, 15, and 30 mol‐% poly(2‐ethyl‐2‐oxazoline) have been synthesized and characterized. The synthesized rod–coil block copolymers display nanofibrillar morphology where the density of the nanofibrills is dependent on the concentration of the poly(2‐ethyl‐2‐oxazoline) coil segment. The conductivity of the diblock copolymers was lowered from 200 to 35 S · cm^?1 with an increase in the content of the insulating poly(2‐ethyl‐2‐oxazoline) block. By contrast, the field‐effect mobility decreased by 2–3 orders of magnitude upon the incorporation of the poly(2‐ethyl‐2‐oxazoline) insulating segment.

     

Effect of Alkyl Side Chains on the Photovoltaic Performance of 2,1,3‐Benzoxadiazole‐Based (‐X‐DADAD‐)n‐Type Copolymers

A family of novel (X‐TATAT)_n‐type conjugated polymers based on the carbazole (X), thiophene (T), and benzoxadiazole (A) moieties is designed and explored as electron‐donor materials for organic bulk heterojunction solar cells. Incorporation of the branched side chains of different size and shape affects significantly the optoelectronic properties of the materials, particularly frontier energy levels of polymers translated to the open circuit voltages of the photovoltaic cells. The revealed unprecedented correlation between the parameters of the solar cells (V _OC, fill factor (FF), J _SC) and bulkiness of the alkyl side chains provides useful guidelines for rational design of novel materials for organic photovoltaics.

     

Surface Properties and Antimicrobial Activity of Poly(sulfur‐co‐1,3‐diisopropenylbenzene) Copolymers

Poly(sulfur‐co‐1,3‐diisopropenyl benzene) copolymers with varying compositions are synthesized from elemental sulfur and 1,3‐diisopropenyl benzene by melt polymerization. The resulting polymers are spin‐coated onto silicon wafers, and their thin‐film properties (thickness, surface composition, hydrophobicity, swellability, roughness, and morphology) are studied. The surface composition of the polymer films (determined by X‐ray photoelectron spectroscopy) indicates that the carbon‐containing repeat units of the polymer segregate to the air–polymer interface, so that the resulting surfaces are hydrophobic. This is in line with results from surface plasmon resonance spectroscopy measurements, which indicate that the materials are protein‐adhesive. Atomic force microscopy reveals that all materials are quite rough and show signs of microphase separation. Antimicrobial assays reveal that the materials are moderately active against Escherichia coli.     

Synthesis and Gas‐Transport Properties of Novel Copolymers Based on Tricyclononenes Containing One and Three Me3Si‐Groups

In this work the authors report the preparation of new addition copolymers based on 3‐trimethylsilyltricyclononene‐7 (TCNSi1) and 3,3,4‐tris(trimethylsilyl)tricyclononene‐7 (TCNSi3). A number of high molecular weight copolymers are synthesized with the content of TCNSi3 units from 5 up to 20 mol% in the presence of catalyst Pd(OAc)₂/[Ph₃C]⁺[B(C₆F₅)₄]⁻ with the yields of 50%–80%. The obtained copolymers are amorphous. They possess large free volume elements (R ₃/R ₄) based on positron annihilating lifetime spectroscopy analysis and Brunauer–Emmett–Teller surface area up to 640 m² g⁻¹. Permeability coefficients of the obtained copolymers are determined for a wide range of gases He, H₂, O₂, N₂, CO₂, CH₄, C₂H₆, C₃H₈, n‐ C₄H₁₀. The correlation between the content of TCNSi3 units and gas permeation parameters of the resulting copolymers is explored. It is found that the introduction of TCNSi3 moieties results in the rise in gas permeability of the corresponding copolymers. Moreover, increase in TCNSi3 content in the copolymer leads to an increase of gas permeability.

     

Self‐Assembly and Responsive Behavior of Poly(peptide)‐Based Copolymers

Well‐defined copolymers synthesized by combining poly(ethylene glycol) (PEG) and amino acid based building blocks are investigated with regard to their helical rigidity and self‐assembly. Optical active block copolymers reported here are designed to have a pendant amino acid and polymerizable group, that is, isonitrile in order to induce helix formation and reduce the mobility of polymer chains by forming a hydrogen bond network so that a helix with reasonable rigidity can be obtained. Due to the amphiphilicity and a relatively shorter PEG as a coil, these polymers form micelles as observed under transmission electron microscopy in which copolymers PEG₁₀₈‐b‐PPIC₇₆₄ and PEG₁₀₈‐b‐PPIC₁₀₂₀ appear to be evolving into nanoparticles with a size distribution of 100–200 nm. Circular dichroism spectroscopy is employed to study the nature of the helix and its rigidity. The folding and unfolding of polymer helix as a result of the ability of a selective solvent to form/disrupt hydrogen bonds with the peptide linkage is also discussed to highlight the responsive nature of the polymer.     

n‐Type Copolymers with Fluorene and 1,3,4‐Heterodiazole Moieties

Summary: The successful realization of n‐channel field‐effect transistors requires the application of semiconducting polymers with high electron mobility (n‐type). However, reports on n‐type polymers are rather scarce in the literature. Therefore, the development of polymers with suitable electron transport properties is particularly challenging for the synthetic chemistry. Main chain polymers with strong acceptor units, such as 1,3,4‐heterodiazoles, are potential candidates for electron transport materials in electronic devices. The fluorene unit is another ring system with interesting physical and chemical properties, which is often used in rigid‐rod, main chain polymers. The present work introduces the synthesis of organo‐soluble copolymers consisting of alternating fluorene‐, 1,3,4‐heterodiazole, and, in some cases, additional 2,5‐dialkoxyphenylene units in the main chain. The reported synthesis involves modified classical polycondensation as well as the tetrazole route. We demonstrate the possibility of exchanging oxygen in the heteroaromatic ring with sulfur using Lawesson's reagent during the ring closure reaction. An alternative structure of the heterocyclic ring with N‐phenyl in the oxygen position is feasible using the tetrazole synthetic route. The chemical and electrochemical properties of the copolyfluorenes are investigated in detail. Some of the synthesized copolyfluorenes have also been used for the preparation of “electron‐only” devices enabling the calculation of the electron mobilities. Further, an organic field‐effect transistor (OFET) characteristic was shown.

OFET characteristics of the polymer 12b .     

New Second‐Order Nonlinear Optical Polymers Derived from AB2 and AB Monomers via Sonogashira Coupling Reaction

In this paper, a facile route was designed to prepare a new AB₂‐type polymer P1 via simple Sonogashira coupling reaction, also its corresponding linear analog ( P2 ) was obtained from AB monomer for comparison. Despite the relatively lower loading density of the effective chromophore moieties, P1 demonstrated higher second‐harmonic coefficient (153.9 pm · V^?1) than that of P2 (98.2 pm · V^?1), due to the three‐dimensional spatial isolation effect of the hyperbranched structure. The good results of P2 also indicated that the ladder shape may help to solve the problem existing in main‐chain polymers, the low poling efficiency.

     

Synthesis and Characterization of Conducting Copolymers of (S)‐2‐Methylbutyl‐2‐(3‐thienyl)acetate with Pyrrole and Thiophene

Polymerization of methylbutyl‐2‐(3‐thienyl)acetate (MBTA) was achieved by constant current electrolysis at low temperature. Subsequently, the syntheses of block copolymers of polyMBTA were accomplished in the presence of either pyrrole or thiophene by constant potential electrolysis. Moreover, the copolymer of MBTA with thiophene was obtained with constant potential electrolysis.

The synthesis of monomer MBTA.