Electronic deactivation in single chains, nano-aggregates and ultrathin films of conjugated oligomers

Fluorescence spectra, quantum yields ΦF, decay curves, and fluorescence anisotropies of oligothiophenes and oligophenylenevinylenes with varying chain lengths are determined in the dissolved state, in nano-aggregates and in ultrathin films. ΦF decreases in the series monomer > aggregate ≈ disordered film > oriented film by four powers of ten, whereas the average decay times remain unchanged. The orientational relaxation time is 35 ps in condensed oligothiophenes. The strong increase of ΦF with disorder is mainly attributed to the increasing density of luminescence centers.