Thiophene based polymeric materials for opto-electronics: Design, synthesis and characterization

This dissertation presents a novel attempt in employing high mobility conjugated polymers in formulating the photorefractive (PR) materials. Conjugated thiophene polymers and oligomers have been known to exhibit photoconductivity and are also known to be relatively efficient charge transporters. Charge carrier mobilities as high as 3.0 cm{dollar}rmsp2cdot Vsp{lcub}-1{rcub}cdot ssp{lcub}-1{rcub}{dollar} have been observed in some of the well-defined oligothiophenes. The PR response time is dependent on the photoconductivity, which in turn depends on the quantum yield of charge carrier generation, and the mobility of the carriers. Hence, faster response times are expected for the conjugated polymer based PR materials, owing to their high mobility.; We have synthesized second order non-linear optical (NLO) chromophore functionalized thiophene copolymers in order to realize the fast responsive photorefractive effect. The NLO chromophore functionalized copolymer, poly(3-octylthiophene-co-N-(3-thenyl)-4-amino-2-nitrophenol, POMDT, was soluble in common organic solvents. 3-octylthiophene was used as a comonomer to achieve the solubility. Thick films with good optical quality could be obtained from POMDT by solution casting. The POMDT polymer was further functionalized with photo-cross-linkable cinnamoyl groups. The POMDT and cinnamoylated POMDT copolymer derivatives exhibited small second order NLO response. Enhanced second order NLO response was achieved by dispersing photo-cross-linkable 3-cinnamoyloxy-4- (4-(N,N-diethylamino)-2-cinnamoyloxy phenylazo) nitrobenzene (CNNB-R) chromophores. The poled, photo-cross-linked, dye doped copolymer exhibited relatively large second order NLO effects ({dollar}rm dsb{lcub}33{rcub}=18.6{dollar} pm/V and 3.3 pm/V at 1.064 and 1.542 {dollar}rmmu m{dollar} respectively). The NLO properties of the photo-cross-linked samples were stable at room temperature.; Photoconductivity measurements were also carried out for the CNNB-R/POMDT polymer composite films. The polymer composite films exhibited photocurrents in the order of dark conductivity ({dollar}rm 10sp{lcub}-12{rcub}Omegasp{lcub}-1{rcub}cmsp{lcub}-1{rcub}{dollar}) at 730 nm. The measured photo-currents were, however, one to two orders of magnitude higher than the dark current, when sensitized with 1 to 2 wt. percentage of TNF. The two beam coupling (TBC) technique was used to study the PR characteristics of this composite film. The composite film showed asymmetric energy transfer which indicates the PR nature of the thiophene based polymeric material.; The dark conductivity of the composite film was observed to be slightly lower when plasticized with DOP. Photoconductivity of {dollar}rm 4.0times10sp{lcub}-10{rcub}Omegasp{lcub}-1{rcub}cmsp{lcub}-1{rcub}{dollar} was measured for the TNF sensitized plasticized composite film at 15.3 mW laser power with a bias of 100 V. The mobility of the copolymer, however, decreases upon adding plasticizer. The plasticized composite film showed excellent asymmetric energy transfer between the two incident beams. The TBC gain was calculated as 24.5 {dollar}rm cmsp{lcub}-1{rcub}{dollar} for the plasticized composite film, which is about two orders of magnitude higher than the unplasticized composite. Attempts were made to synthesize low Tg epoxy polymer with disperse orange 3 and p-aminobenzaldeyde 1,1-diphenyl hydrazone chromophores in order to replace the inert plasticizer and small molecular NLO chromophores. But phase separation of the polymers occurs upon blending of the POMDT with NLO polymer.; A new, flexible, hydrogen bond forming urethane group functionalized thiophene polymer, poly (2-(3-thienyl)ethanol n-butoxy-carbonyl methyl urethane) (PURET) was synthesized in order to realize compatible blends. (Abstract shortened by UMI.)...