Structure of Thiophene-Based Regioregular Polymers and Block Copolymers and Its Influence on Luminescence Spectra

Article abstract of DOI:10.1021/j100010a036

Two approaches toward control of the luminescence wavelength of polythiophenes have been explored: (i) block copolymers in which oligothiophene blocks alternate with oligosilanylene blocks and (ii) regioregular polythiophenes in which oligothiophene sequences are delimited by n-octyl substituents placed in a "head-to-head" fashion on adjacent rings.Both methods aim at restricting the ?-conjugation to the oligothiophene sequences.The block copolymer approach is very effective, whereas the (solution) luminescence spectra of the regioregular polymers are strongly red-shifted with respect to absorption and confined to a narrow range of wavelengths.This is due to the quinoid character of the excited singlet state, in which there is a strong electronic driving force toward coplanarity of adjacent thiophene rings, which offsets the steric hindrance of the octyl substituents and increases the size of the conjugating ?-system.This explanation is supported by calculations and by spectral data of substituted bithiophenes.