Exciton and vibronic effects in the spectroscopy of bianthracene in supersonic beams

Abstract

Excitation and dispersed fluorescence spectra of 9,9′-bianthracene in a supersonic expansion are reported. The spectra are anthracene-like, indicating that the rings are weakly coupled. Exciton effects are considered in the interpretation of the spectra. The torsional potential in S1 is modeled as a double-well (Gaussian perturbation on a one-dimensional harmonic oscillator) with barriers to perpendicularity and planarity of ∼30 and ∼1100 cm−1, respectively. The S0 torsional potential shows negative anharmonicity which is modeled as a quartic perturbation. Anthracenic modes in S1 and S0 are also assigned. Finally, measurements of S1 fluorescence lifetimes up to ∼6000 cm−1 excess energy in the excited state show no evidence of charge transfer.