Chiroptical properties of highly ordered di[(S)-2-methylbutoxy] substituted polythiophene and poly(p-phenylene vinylene)

Circular dichroism (CD) spectroscopy is used to study the nature of the excited state of optically active di[(S)-2-methylbutoxy substituted polythiophene (PDMBT) in small aggregates with a high degree of intrachain and interchain order. The observed CD effects indicate oscillator coupling between chains in the excited state. The photoluminescence of the PDMBT aggregates is characterized by a very small Stokes shift (< 0.09 eV) and is circularly polarized but less intense than of free PDMBT chains in solution. The decrease of luminescence efficiency in the aggregated phase can be explained by the exciton coupling observed in CD and results in a non-radiative low-energy state. Similar results are obtained for optically active poly(p-phenylene vinylene).