On the origin of optical activity in polythiophenes

Optically active substituents attached as sidechain to p-conjugated polymers provide a particularly interesting and revealing tool to study the nanoscopic and mesoscopic supramolecular organization of p-conjugated polymers in general. Chiral substituents allow the properties of these polymers to be studied with circularly polarized light in both absorption and emission. Here we describe a comprehensive investigation on the structure and optical properties of poly{3,4-bis[(S)-2-methylbutoxy]thiophene} (PBMBT) as an example to elucidate the molecular origin of the chiroptical effects in chiral conjugated polymers. The chiral side chains of PBMBT induce very strong bisignate circular dichroism (CD) effects in the p–p* absorption when the polymer is in an aggregated phase. The anisotropy factor in absorption (gabs) is as high as 8×10-2. The photoluminescence of PBMBT aggregates is characterized by a very small Stokes shift