Photoexcitations of thiophene-based copolymers with tunable energy gap

The photoluminescence and the cw photoinduced absorption spectra of a series of conjugated polymers obtained by the copolymerisation of 3-butylthiophene and 3,4-dibutylthiophene in different ratio are reported. By varying the copolymer chemical composition it is possible to tune the intensity and the colour of the luminescence spectra in the whole visible range. The PA bands, associated to charged species and triplet states, are also affected by the copolymer composition. We show that disorder, controlled by interring rotations, is the tuning factor for the photoexcitations in these materials.