Influence of the degree of conjugation on excited state lifetimes in phenylene-based materials

Phenylene-based materials are of particular interest for applications in organic luminescent devices. To gain deeper insight into the emissive properties of this class of materials, we have systematically studied the relation between the degree of conjugation and singlet exciton lifetimes. Two classes of phenylenes are investigated by time resolved frequency domain spectroscopy: oligo-para-phenylenes (OPPs) with n-alkyl substitutions at the central phenylene ring of the molecule and ladder-type-oligo-para-phenylenes (LOPPs) featuring rigid backbones with fixed interring twist angles. Additional quantum yield (QY) measurements allow to assess the intrinsic lifetime of the radiative decay. The experimental data are compared to the results of quantum-chemical calculations yielding an excellent agreement for both the classes of materials.