STRUCTURE PROPERTIES OF CONJUGATED CONDUCTIVE POLYMERS .2. 3-ETHER-SUBSTITUTED POLYTHIOPHENES AND POLY(4-METHYLTHIOPHENE)S

Two series of 3-substituted polythiophenes (PTs) and poly(4-methylthiophene)s (P4MTs) having the substituents containing 8 atoms in the backbone with oxygen as the first atom bonded to the thiophene ring, C7H15O-, C4H9OC2H4O-, and CH3OC2H4OC2H4O- for the former series and having the first two substituents for the latter series were synthesized by chemical polymerization using ferric chloride as the oxidizing agent and characterized using thermal analysis, various spectroscopic methods, cyclic voltammetry, and conductivity measurement. For the first series, in comparison with poly(3-octylthiophene) (P3OT; lambda(max) = 480 nm), a replacement of the first carbon attached to the thiophene ring by an oxygen atom leads to a decreased band gap (lambda(max) = 580 nm) due to the electron-donating nature of the oxygen. Further substitution on the 4-position of the thiophene ring with the methyl group of the 3-substituted PT with the substituent C7H15O- leads to an increase in the band gap due to a decrease in conjugation caused by a steric hindrance of the methyl group as reflected in the change of lambda(max) from 580 to 420 nm. But its oxidation potential (0.76 V) is lower than that of P30T (1.01 V) due to electron donation to the pi system by the oxygen. Additional replacement of the third carbon atom by an oxygen atom in the side chain (giving C4H9OC2H4O-) improves the conjugation (as reflected by an increase in lambda(max) to 530 nm and a decrease in the oxidation potential to 0.6 V) due to a strong interaction between neighboring side chains, such that no thermochromism is observed before a decomposition of side chains.