Theoretical study on geometry and spectroscopic properties of 1,1′-binaphthyl in the electronic ground and first excited singlet states

Abstract

Equilibrium geometries for the electronic ground and first excited singlet states of 1,1'-binaphthyl have been calculated by minimization of the total energy with respect to all internal coordinates. Using these results, an interpretation of the fluorescence S 1→ S 0 and absorption spectra S m ← S 0 and S n ← S 1 in rigid and fluid solutions is given. For the first time the equilibrium geometry of the first excited singlet state of 1, 1′-binaphthyl has been calculated. On excitation to the S 1 state the dihedral angle θ between the two naphthalene moieties is de- creased from 61 ° to 41 °. A detailed survey of CH bond lengths in the S 0 and S 1 states has been given. This result should be of particular importance for the theoretical treatment of radiationless transitions. Using equilibrium geometries for the S 0 and S 1 states a satisfactory interpretation of the S m ← S 0 and S n ← S 1 absorption spectra as well as of the fluorescence spectra in fluid and rigid solutions can be given. Concerning the S n ← S 1 absorption spectrum in fluid solution, the calculations predict a strong absorption (A ← B transition) in the still uninvestigated region of energies lower than 11000 cm −1. From the results of this paper and of other calculations it can be concluded that the Warshel-Karplus method yields reliable equilibrium geometries for electronic ground and excited states of unsaturated hydrocarbons [22,23].