The effect of conjugation length on triplet energies, electron delocalization and electron–electron correlation in soluble polythiophenes

Triplet energies from a family of polythiophenes in which effective conjugation length is controlled by steric torsion have been measured for the isolated polymer chain regime, i.e., benzene solution. Triplet states are stabilized by some 0.6 eV as effective conjugation length increases up to ca. 6 repeat units, then saturation occurs. This triplet stabilization must occur by electron delocalization and implies that singlet states are stabilized as conjugation length increases by a combination of electron and exciton delocalization.