Electronic spectroscopy and dynamics of the monomer and Arn clusters of 9-phenylfluorene

Abstract

The spectrum of the S1 electronic state of jet-cooled 9-phenylfluorene–Arn, n=0–4, has been measured by two color resonant enhanced multiphoton ionization spectroscopy. The cation ground states of these complexes have also been studied by mass analyzed threshold ionization (MATI) spectroscopy in a 1+1 excitation process with various intermediate states in S1. Ab initio calculations in conjunction with the spectroscopy have determined that the phenyl ring at the 9 position is perpendicular to the plane of the fluorene moiety yielding an overall symmetry of Cs. The Ar complexes for n=1–3 exhibit multiple isomers which are identified in the S1 spectrum and confirmed by MATI spectroscopy. The structure of these isomers is determined by spectral analysis and additivity rules as well as atom–atom calculations using a Lennard-Jones potential. Vibrational dynamics from selected S1 vibronic levels are observed by the appearance of the picosecond or nanosecond time delayed MATI spectra. Vibrational redistribution and dissociation of the clusters are measured with nanosecond and picosecond time resolution. It is found that different isomers of the n=1 cluster show dramatically different rates of redistribution for several vibronic bands.