OPTICAL-PROPERTIES OF QUASI-ONE-DIMENSIONAL THIOPHENE-BASED OLIGOMERS

We have studied optical properties of one-dimensional oligothiophenes and thiophene-based oligomers. The thiophene-based oligomers have the well-barrier-well structures in quasi-one-dimensional backbone chains, where the well parts are the oligothiophenes with different conjugation lengths and the barrier parts are nonvisibly luminescent materials with larger energy gaps. The chain-length dependence of the optical properties of oligothiophenes shows that excitons are localized within two thiophene rings and the luminescence decay is controlled by the diffusion of localized excitons. Furthermore, luminescence properties of thiophene-based oligomers such as luminescence yield, luminescence lifetime, and luminescence wavelength can be controlled by changing the conjugation length of the well part and the barrier structure. Spectroscopic analysis and molecular-orbital calculations show that the exciton localization and radiative recombination processes are affected by the rotational motion of thiophene rings.