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A series of new organic dyes, 2-(2,6-bis((E)-2-(5′-hexyl-2,2′-bithiophen-5-yl)vinyl)-pyran-4-ylidene)-2-cyanoacetic acid (OD-1) and 2,2′-(2-((E)-2-(5′-hexyl-2,2′-bithiophen-5-yl)vinyl)-1H-indene-1,3(2H)-diylidene)bis(2-cyanoacetic acid) (OD-2), were synthesized as a sensitizers for the application of dye-sensitized solar cells (DSSCs). The introduction of the 5′-hexyl-2,2′-bithiophene units as an electron donor group and 2,6-dimethyl-pyran-4-one or 1,3-indandione as a π-spacers units increased the conjugation length of the sensitizers and thus improved their molar absorption coefficient and light harvesting efficiency.

Two fullerene-terthiophene dyads without hexyl chains (3T-C₆₀) and with hexyl chains (3TH-C₆₀) on the terthiophene substituent are synthesized by 1,3-dipolar cycloaddition of corresponding azomethine ylides to C₆₀. The cyclic voltammetry studies indicate no apparent electronic communication between the terthiophene pendent group and the fulleropyrrolidine core in the ground state. However, a significant florescence quenching is observed for 3T-C₆₀ and 3TH-C₆₀, compared to their fluorescent terthiophene (3T) and 3TH precursors, respectively, suggesting the occurrence of strong intramolecular electron/energy transfers in the photoexcited state. Furthermore, these new fulleropyrrolidine derivatives are applied as electron acceptors to fabricate poly(3-hexylthiophene) (P3HT) based bulk heterojunction solar cells. The incident photon-to-current efficiency (IPCE) value of the P3HT/3T-C₆₀ device is significantly higher than that of the P3HT/PCBM cell in wavelengths of 350-420 nm. This finding provides direct evidence for the contribution of 3T excitons to the photocurrent. Replacing 3T-C₆₀ with 3TH-C₆₀ effectively improves the morphology of the photoactive layer and widens the window of optimal D/A ratios, raising the power conversion efficiency (PCE) from 2.14% to 2.54%. Importantly, these devices exhibit superior stability of PCE against high-temperature aging.

A Cu2+-specific colorimetric sensor of bis-triazole-appended azobenzene receptors I and II was designed and synthesized. Receptor II shows high selectivity toward Cu2+ in acetonitrile/water (80:20, v/v) solution based on the internal charge transfer (ICT) mechanism. The tridentate coordination behavior was proposed with 1:1 stoichiometry between receptor II and Cu2+. Herein, the Cu2+ gives rise to a large change in the absorption spectra (from red to pale yellow) that is clearly visible to the naked eye.

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.

The oxazole and indole based heterocyclic photochromic fulgides were synthesized from their corresponding fulgenic acid derivatives by clay catalysed microwave irradiation methodology. Improved yields of fulgides were observed by the microwave irradiation method as compared other chemical methods employed so far. The proportions of clay (montmorillonite KSF) and isopropenyl acetate play a key role in increasing the yields of fulgides.

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

Azobenzene-based monomers and their polymers containing donor or acceptor groups at terminal positions have been synthesized. The liquid crystalline (LC) mesophase stability of one type of polymer and mixtures of donor or acceptor substituted polymers have been investigated. Mesophase formation and stability of the mixtures were studied using differential scanning calorimetry (DSC) and a hot-stage optical polarizing microscope (HOPM). The mesophase stability of the mixtures was better than those of the individual components. Binary mixture studies of acceptor monomers (a) and donor monomers (d) show that the pure low molecular weight compounds did not form any molecular aggregates and failed to show LC properties, whereas the mixture of donor substituted azobenzene and acceptor substituted azobenzene exhibits LC property. In the case of polymers, the individual acceptors (A) or donors (D) exhibit LC property, and their mixture stabilizes the crystallinity of the mesophase. The results of correlation studies of various proportions of mixtures of a/d and A/D with regard to LC properties and their mesophase stabilities are presented

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.

An oxadiazole based electron transporting (ET) unit was glued to the heteroleptic Ir(III) complex (TPQIr-ET) and used as a dopant for phosphorescent organic light-emitting diodes (PhOLEDs). It shows superior device performance than the dopant without the ET unit (TPQIr) due to the balanced charge carrier injection by the ET unit.

Two 5-arylidenebarbituric acid derivatives (IH and IM) have been synthesized by the Knoevenagel condensation of barbituric acid with 4-N,N-dimethylamino benzaldehyde and studied for anion sensing activities. Both receptors sense fluoride ion with high selectivity and sensitivity and the sensing action has been demonstrated by naked eye detection, UV-visible absorption, and fluorescence spectral changes in the presence of F(-). Indeed, the F(-) sensing mechanism for receptor IH depends on F(-) ion concentration. While at higher concentrations F(-) forms strong hydrogen bonding interaction with the N-H proton of the receptor, at lower concentrations sensing is influenced by the deprotonation of the methylene proton, followed by the chemical reaction, which is also confirmed by the (1)H-NMR technique. On the other hand, when replacing the N-H proton with a methyl group, IM does not show any concentration dependent behaviour with F(-). The F(-) concentration dependent sensing is attributed to the changes in the receptor-anion interaction equilibrium, where at higher F(-) concentrations, F(-) interacts with the receptor through hydrogen bonding and at lower concentrations it induces a chemical reaction.

A highly selective and sensitive near-IR optical sensor, benzoselenadiazole based diarylamine (TBS-HN), for fluoride (F(-)) has been designed and synthesized. TBS-HN also shows turn-on ratiometric fluorescence signaling in the presence of F(-) by inhibiting the excited state intramolecular proton transfer (ESIPT) processes.

Fulgimide and various size and electronic nature of substituents on the terminal position of azobenzene in the pendant homo/copolymethacrylates were synthesized. Differential scanning calorimetry analysis indicates the homopolymer possessing C-form fulgimide unit exhibited higher T m than that of E-form of the homopolymer and revealed C-form is highly ordered. Thermal stability suggests azobenzene homopolymers with electron donating substituents have high thermal stability than electron withdrawing substituents. Polarized optical microscopy observation disclosed homopolymers viz., NI, CY, FL, ME, and T-ME exhibited liquid crystalline mesophases between their T m and T i . Optical properties of homo/copolymers were investigated by UV-vis and fluorescence spectroscopy. UV-vis spectroscopy displayed C-form fulgimide absorption in F-co-FL around 482 nm which is around 40 nm lesser than C-form of substituted azobenzene copolymers. Similarly, fluorescence pattern of F-co-FL by UV irradiation exhibited emission intensity slowly increased to certain level then decreases with two new emissions at 430 and 480 nm attributed to terminal position of fluorine atom on azobenzene destabilizes polar form (C-form) fulgimide unit in the copolymer.