Conjugated polymers are organic semiconductors and, as such, are of great potential importance for device fabrication. Such devices include light-emitting diodes, light emitting electrochemical cells, photovoltaic cells, thin-film transistors, and plastic lasers. The discovery of electroluminescence in conjugated polymers gave an impetus to the development of light emitting devices for display technology. New monosubstituted poly(phenylacetylene)s (PPAs) P1-P6 were synthesized by using the transition metal catalyst WCl6 and organometallic cocatalyst Et3SiH in toluene at rt in good yields. The polymers produced were brown to dark purple solids and soluble in organic solvents such as toluene, chloroform, dichloromethane, THF, xylene etc. The weight-average molecular weight (Mw) was ranging from 4 × 104 to 5 × 105. IR and NMR studies confirmed the structure of the polymers. The stereo structure of the polymers was confirmed by 1H NMR and it can be concluded that WCl6 produces trans-rich polymers together with less than 10% cis-rich polymers. The polymers were found by TGA studies to begin losing weight at ca. 350 ℃ under nitrogen, which shows that P1-P6 are thermally more stable than poly(phenyl acetylene) (PPA). UV-visible spectra of P1-P6 showed large red-shifted absorption maximum as compared with that of PPA. The fluorescence spectra of polymers P1, P4, P5 and P6 showed blue emission (~414 nm), while P2 and P3 showed purple emission upon excitation of their THF solution. A new disubstituted polyacetylene was synthesized with the transition metal catalyst NbCl5 with the cocatalyst n-Bu4Sn in toluene at RT in good yield. The polymer was bright fluorescent yellow color solid with an Mw of ca. 2.8 × 105. The polymer was found to be highly soluble in most of the organic solvents such as toluene, chloroform, dichloromethane, THF, xylene etc. The structure of the polymer was confirmed by spectroscopic analysis such as NMR and IR. The polymer was thermally stable due to the presence of phenylethynyl group at the para-position, which showed 5% weight loss at about 386 ℃. The polymer showed absorption maximum at ca. 292 nm and the photoluminescence showed blue-green emission upon excitation at their absorption maximum in THF solution. Solid state absorption and emission showed no aggregation, due to the steric hindrance of the tolane and hexyl group on the polymer backbone. The optical and thermal properties of the polymer PhPO were found to be much better than the parent polymer PPhA-6. A series of new poly(phenylene ethynylene) homopolymers (PE-1 and PE-2) copolymers (PE-3 to PE-7), with phenyl, fluorene, carbazole and pyrene units, were synthesized by the Pd catalyzed coupling reaction in good yields. The structures of the polymers were confirmed by IR and NMR spectroscopies and their weight average molecular weights were measured by GPC in THF eluent. The polymers in general showed the temperature of 5% weight loss appeared at ca. 281-358 ℃. The polymers exhibited emission in blue region and blue-green-light in THF solution upon excitation at their absorption maximum. Due to aggregate formation, polymers showed red-shifted absorptions and emissions in their solid state films as compared with their solutions. Solvent-induced aggregation of PE-1 and PE-2 showed strong polymer chain interaction both in absorption and emission spectra. While the solvent-induced aggregation of polymers PE-3, PE-5, and PE-6 showed strong polymer chain interaction in the emission spectra and weak polymer chain interaction in the absorption spectra. Interestingly the solvent-induced aggregation of PE-4 and PE-7 showed very weak polymer chain interaction in both absorption and emission spectra. We have synthesized various oligo(phenylene ethynylene)s (OPEs) by Pd catalyzed coupling reaction with good yields, in which alkyl and alkoxy groups were introduced as side chains and fluorene, carbazole and pyrene were introduced as alternating aryl units in their chromophoric chain. The oligomers are highly soluble in most of the organic solvents such as chloroform, toluene, ethyl acetate, THF, dichloromethane, DMSO, DMF etc. The structure of the oligomers was confirmed by means of various spectroscopic analyses. The oligomers in general showed the weight loss temperature of 5% appeared at ca. 312-485 ℃, and the weight retention at 900 ℃ was much higher, i.e., 80 to 40%. The thermal properties of oligomers showed liquid crystalline phases for OPE-5 and OPE-11 and they showed nematic schlieren textures, while OPE-6 showed smectic focal conic textures upon cross-polarized optical microscope observation. The solid state film of oligomers showed red-shifted emission and absorption from their solution spectra due to aggregate formation in the solid state. Finally, we have synthesized polymer nanotubes and carbon nanotubes using the poly(phenylene ethynylene)s of PE-3 and PE-6 using alumina membrane template with an average pore size diameter of ca. ~200 nm. The carbon nanotubes were prepared by heating the alumina membrane template containing the polymer tube nanostructures at 700 ℃. By this template nanostructuring method, both polymer nanotubes and carbon nanotubes were formed with a very good mechanical strength. The tubes are circular hollow and the surface was very smooth. After complete removal of the alumina membrane, the average outer diameter of polymer nanotubes and carbon nanotubes were in well agreement with the pore diameter (~200 nm) of alumina membrane template. The carbon nanotubes prepared from polymer PE-6 at 700 ℃ are turbostatic in nature.