The electrochemical and optical properties of a series of low band gap alternating polyfluorenerncopolymers and polythiophene derivatives with quinoxaline units were characterized optically andrnelectrochemically for use in polymer solar cells. The polymers have band gaps ranging from 2.1-0.8 eV.rnA structure-property correlation, which sheds light on the design of efficient devices, was observed.rnOxadiazole-containing polymers were also optically and electrochemically characterized forrnpolymer/polymer blend devices. Most of the polymers gave good electrochemical reversible reductionrnbehavior with very high ionization potential (> 6.1 eV) and very high electron affinities (3.5-3.6 eV). Arnseries of alkoxyphenyl-substituted fluorene units together with different amounts of a hole-transportingrntriphenylamine-substituted fluorene units designed for light-emitting devices were characterized. Allrnpolymers show high photoluminescence efficiency and light emission in the blue spectral region.rnElectrochemical studies shows more pronounced reversible behaviour and hence, improved holetransport,rnas the ratio of the hole-transporting unit is increased. The electroluminescence quantumrnefficiencies of the devices increase six times going from P10 to P11. Compared with P11, polymers P12rnand P13 show lower efficiencies in devices. These findings indicate the presence of an optimal polymerrncomposition, where balance between the charge-carrier mobilities has been reached. Anthrancene andrnbenzothiadiazole containing polyfluorene copolymers (P14-P16) were also characterized. Polymers P15rnand P16 show high photoluminescence efficiency while polymer P15 does not show any significant lightrnemission up to 8.0 V. The results also show the need for balance of electron and hole injection andrntransport in polymer light emitting diodes. The photovoltaic properties of devices made using a highlyrnconducting polymer electrode, from vapor-phase polymerized poly(3,4-ethylenedioxy)thiophene (VPPrnPEDOT) on glass substrate as an anode and a polyfluorene copolymer, APFO-3, mixed with PCBM asrnthe active layer. The device performance was compared with that of devices made with PEDOT-PSS onrnglass substrates. The device performance of solar cells constructed from the VPP PEDOT made on arnflexible and transparent substrate as a cathode material and ITO/ PEDOT:PSS films supported on glassrnsubstrates as anode were characterized. The devices have shown good electrical and optical responses.rnThe electrochromic polymer PEDOT-PSS spin coated on ITO/glass was patterned with soft lithographic method in order to diffract the incident light, and thereby modify absorption of light by the film to improve the electrochromic efficiency of the polymer. The absorbance peak at around 610 nm wasrnfound to be much higher in the patterned PEDOT-PSS film than the one observed in the unpatternedrnfilm. Values of coloration efficiencies varying from 107 to 174 cm2/C were obtained for three differentrnunpatterned PEDOT-PSS films, where as for three different patterned PEDOT-PSS films higher valuesrnranging from 204 to 371 cm2/C were found. These increased values of the electrochromic efficiencies are attributed to diffraction. The electrochromic behaviours of some polythiophenes were also investigated in bilayer system. The solvatochromic and thermochromic behaviors of phenyl-substituted polythiophenes were studied. The pristine polymers, upon dissolution in chloroform, exhibited blueshiftedrnabsorption. The solid films of the polymers showed significant blue-shifted as well as red-shiftedrnabsorptions when heated. While the addition of methanol to the chloroform solutions of the polymersrncaused dramatic chromic changes and development of red-shifted spectra for many of the polymers investigated, the symmetrically phenyl-substituted and sterically hindered polymer (polymer P1) does not show significant changes. These chromic behaviors have been examined in terms of substituent effects and attempt has been made to explain these effects by calculating the energy barrier for rotation to a planar structure using the HF SCF method and 3-21G* basis set