4-(9-Anthryl)aniline. 2. Two Weakly-Coupled Electronic States and their Torsional Potentials Evaluated from the Laser-Induced Fluorescence Spectra in a Supersonic Jet

Abstract

Laser-induced fluorescence excitation spectra of 4-(9-anthryl)aniline (AA) have been observed in a free jet. A detailed analysis of the spectra reveals the presence of a new low-lying charge-transfer (CT) state. Taking account of a coupling of this CT state with the locally excited (LE) state, we reproduced the spectra and evaluated the torsional potentials of the ground, the LE, and the CT states. In an isolated AA molecule, the CT state is nonperpendicular and charge separation is incomplete. The presence of the NH2 substituent is responsible for the low-lying CT state while the flexibility in torsional motion yields the nonperpendicular CT state. These findings are the key to understanding the so-called multistate CT in 4-(9-anthryl)dimethylaniline and its homologues.