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A series of donor-acceptor low band gap polymers (DINIBT-C8, DINIBT-C10 and DINIBT-EH) containing 5,10-dihydroindolo[3,2-b]indole (DINI) as an electron donating unit and benzothiadiazole (BT) as an electron accepting unit with various kinds of alkyl chains (octyl; C8, decyl; C10 and ethyl hexyl; EH) on the donor unit have been designed, synthesized, and characterized for bulk heterojunction polymer solar cell applications. Due to the presence of long alkyl chains on the donor unit, all the polymers showing good solubility in common organic solvents. The frontier orbital energy levels of polymers were calculated using cyclic voltametry analysis. The influence of alkyl chains on the photo-physical properties of polymers were carried out. Among the three polymers, the DINIBT-C8 shows higher absorption coverage and good energy level matching with acceptor PC71BM than that of the other two polymers. Thus, the bulk-heterojunction polymer solar cells (BHJ PSCs) were fabricated using DINIBT-C8:PC71BM as an active...

Two series of click chemistry assisted alkoxymethyl-1H-[1,2,3]-triazol-1-yl containing side-chain liquid-crystalline polymethacrylates were synthesized by free radical polymerization technique. Mesogen was linked to backbone through various spacer units. Monomers and polymers were characterized by FT-IR, 1H and 13C-NMR spectral techniques. Thermal stability of polymers was confirmed by thermogravimetric analysis. Mesomorphic property and phase transition temperature of polymers were analysed by differential scanning calorimetry and polarized optical microscopy. Phase transition temperature and mesomorphic property of polymers with respect to insertion of polar alkoxy group on terminal triazole ring and spacer length between backbone and mesogen were investigated. Polymers exhibited grainy like textures under polarized optical microscopy. Spacer length between mesogen and backbone alters phase transition temperature of the polymers.

Supramolecular side-chain liquid crystalline poly(acrylate)s have been prepared by self-assembly of H-bond donor and acceptor complexes through intermolecular complementary hydrogen bond formation. Poly[4-(m-acryloyloxyalkyloxy)benzoic acid]s [m = 6 (P1) and 8 (P2)] were employed as polymer components. Liquid crystalline nicotinic acid derivatives (C1, C2, C3, and C4) were used as complementary H-bond donor/acceptor counterparts. The liquid crystalline properties of the nicotinic acid derivatives, the polymers and their complexes were investigated by DSC and POM. Methylene spacers present at the terminal position of the nicotinic acid derivatives played a key role in mesophase arrangements. The columnar phase exhibited by the nicotinic acid derivatives completely disappeared in the H-bonded complexes to afford a nematic phase, thereby substantiating the complex formation.

Visibly observed photocrosslinkable pendant liquid crystalline polymers containing indolyl based chalcone were synthesized by free-radical polymerization and characterized spectroscopically. The differential scanning calorimetry and polarized optical microscopy were used to examine liquid crystalline property. The photocrosslinking and luminescence properties were monitored by UV-Vis spectrophotometer and spectrofluorimeter, respectively. It demonstrates the chalcone unit did not manifest cis ↔ trans-isomerization reaction along with 2π+2π photodimerization upon irradiation with UV light like other chalcones hitherto reported. The photocrosslinking was visibly monitored in solution through change of fluorescent color to colorless. The spacer lengths play a key role in the reaction. The fluorescence maximum was blue shifted around 70 nm in chloroform solution upon irradiation with UV light confirms the 2π+2π photodimerization of chalcone unit.

Two series of heterocyclic liquid crystalline compounds with [1,2,3]-triazole ring at the terminal position were synthesized and analyzed for mesomorphic properties and its characteristics. Heterocyclic triazole core was introduced in to the target compound through click reaction between aromatic phenolic azide and alkyl propargyl ethers. The structure of the target compounds and intermediates was conformed by the 1 H NMR, 13 C NMR and IR spectral techniques. All the compounds in both the series were exhibited thermotropic liquid crystalline mesophase. These compounds show enantiotropic Smectic A phase on heating and cooling experiments. This was further confirmed using differential scanning calorimetric investigations. Interestingly, earlier reports on non-polar alkyl group attached to [1,2,3]-triazole heterocyclic ring was not showing any liquid crystalline properties but in the present investigation introduction of polar alkoxy group very near to [1,2,3]-triazole heterocyclic ring displayed liquid crystalline properties.

Copolymer containing new thermally reversible click chemistry-assisted triazole-substituted azobenzene and fulgimide units in the pendant F-co-A was prepared by free-radical solution addition polymerization technique. The F and A were also prepared for comparison. The DSC analysis of F indicates that the polymer possessing the C-form of fulgimide unit exhibited higher Tm than that of E-form of the same polymer and revealed that the C-form of fulgimide unit in F is highly ordered. The cis-trans back isomerization behavior of the click chemistry-assisted triazole-substituted azobenzene unit in film A has thermal irreversibility, while in F-co-A it exhibited thermal reversibility. The UV-exposed film of F-co-A heated around Tg leads to cis-trans back isomerization of azobenzene unit and thermally stable C-form of fulgimide which retains its conjugated structure where both the photochromic units are converted into planar conformations and exhibit high fluorescence properties. The fluorescence maxima of C-form in F-co-A red shifted compared with F, because the substituted triazole ring in the azobenzene unit stabilized the C-form of fulgimide unit. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7843–7860, 2008

Three series of side chain liquid crystalline polymers containing terminally substituted biphenyl cinnamoyl esters were synthesized and characterized. The para position in the cinnamoyl group was connected with polymer backbone through various even numbers of methylene spacers. The terminal electron acceptor and donor substituted biphenyl groups were linked to cinnamoyl group through ester linkages. Polarizing microscopic and DSC studies confirm the formation of thermotropic mesophase up on heating. All the polymers exhibited nematic/grainy mesophases. The TGA and DSC studies showed that the nature of the terminal substituents have significant effect on mesophase temperatures as well as in thermal stability of these liquid crystalline polymers. UV light promoted photocrosslinking studies reveal that the clear involvement on photocrosslinking efficiency, although they are linked to the olefinic bond of cinnamoyl group through their ester linkage. It is observed that electron-donating group accelerate the photocrosslinking rate, while acceptor group retard the phase of the reaction on the other hand, the unsubstituted polymers show an intermediate rate.