Photophysics of the naphthalene—anthracene bichromophoric molecular system in a supersonic jet expansion

Abstract

Intramolecular electronic energy transfer (intra-EET) was investigated in an isolated bichromophoric naphthalene (N) and anthracene (A) 1:1 molecular cluster. Investigation of the spectroscopic properties of these chromophores, separately and loosely bound in a van der Waals complex, helps to understand the dependence of the EET rate on the initially excited vibronic level and on the cluster's interchromophoric orientation. Measurement of fluorescence excitation spectra of anthracene, at different anthracene pressures shows bands that can be assigned to dimers of anthracene. From measurement of the anthracene excitation spectrum at increasing naphthalene pressures one can identify other spectral features, characterized by different spectral shifts from excitations of the bare molecule. Some transitions are probably due to a 13.5 cm −1 progression associated with an interchromophore cluster bond. Pressure dependence of fluorescence intensity gives evidence for 1:1 cluster composition, and for a slow intra-EET rate that is associated with an unfavoured orientation of the two chromophores in one of the two possible conformers of the A–N cluster, as supported by a calculation of the cluster geometry and by comparison with a recent study of intra-EET in the A-(CH 2) n -N bichromophoric molecules.