GROUND AND EXCITED SINGLET-STATES OF 4-(9-ANTHRYL)-N,N-DIMETHYL-ANILINE (ADMA) - A SEMIEMPIRICAL QUANTUM-MECHANICAL CALCULATION

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 sin glet 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 pheny l 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 ( mu > 21 D). The effect of solvent is included using the continuum diel ectric model of Onsager. Potential energy curves of five low-lying sin glets in n-hexane, tetrahydrofuran, 1-butanol, and acetonitrile are co nstructed as a function of the torsion angle (pi(1)) about the bond be tween the anthryl and dimethylaniline group and the torsion angle (tau (2)) about the bond joining the phenyl ring and - NMe(2) group keeping the anthryl ring fixed at 90 degrees with the phenyl ring. In solvent s of dielectric constant above 3.0 a dual emission is predicted to occ ur. The intramolecular charge transfer emission takes place from the h ighly polar S-3 State which is stabilized more by the solute-solvent i nteraction. With the increase in solvent polarity, the charge transfer band is predicted to be red-shifted.