Ground and excited singlet states of 4-(9-anthryl)-N,N-dimethyl-aniline (ADMA): a semiempirical quantum mechanical calculation

Abstract

The ground state (S 0) of 4-(9-anthryl)-N,N-dimethylaniline (ADMA) has been fully optimized by the AM1 method. Several low-lying excited singlet states ( S n , n = 1−5) are studied using the CNDO/S-CI method. In the ground state, the anthracene ring lies perpendicular to the phenyl ring while the −NMe 2 group is almost in the same plane as the phenyl ring. The ground state dipole moment is only about 2.0 D while among five singlet states studied here, S 3 has the largest dipole moment ( μ > 21 D). The effect of solvent is included using the continuum dielectric model of Onsager. Potential energy curves of five low-lying singlets in n-hexane, tetrahydrofuran, 1-butanol, and acetonitrile are constructed as a function of the torsion angle (τ 1) about the bond between the anthryl and dimethylaniline group and the torsion angle (τ 2) about the bond joining the phenyl ring and −NMe 2 group keeping the anthryl ring fixed at 90 ° with the phenyl ring. In solvents of dielectric constant above 3.0 a dual emission is predicted to occur. The intramolecular charge transfer emission takes place from the highly polar S 3 state which is stabilized more by the solute-solvent interaction. With the increase in solvent polarity, the charge transfer band is predicted to be red-shifted.