Characterization of oriented oligo(phenylenevinylene) films and nano-aggregates by UV/Vis-absorption and fluorescence spectroscopy

Absorption maxima in spectra of vapor-deposited oligo(phenylenevinylenes) (OPVs) are blue shifted versus solution, revealing strong exciton coupling due to parallel alignment of the film-consitituting molecules. The films are anisotropic, as shown by polarized angular-resolved absorption spectroscopy. OPV nano-aggregates precipitated from solution are also strongly anisotropic, as shown by steady-state and time-resolved fluorescence anisotropy measurements. Introducing bulky substituents into the OPVs reduces the degree of molecular alignment. Fluorescence spectra of OPV films and aggregates consist of several distinct components, which are due to emission from traps below the exciton band. The overall fluorescence quantum yield is shown to depend mainly on the concentration of traps, which in turn is determined by the degree of molecular alignment.