Photoluminescence of thiophene-based copolymers with tunable energy gap

The photoluminescence spectra and the quantum yields of a series of conjugated polymers obtained by the copolymerisation of 3-butylthiophene and 3,4-dibutylthiophene in different ratio are reported. The emission maxima, like the absorption maxima, are tunable in the visible by varying the fraction f of disubstituted monomers. By increasing f there is a blue shift of the spectra while the Stokes shift exhibits a considerable increase both in the solid state and in solution. The role of ring rotations in the structural relaxation of the excited state and in the non radiative recombination channels is discussed.