Ab initio study of aromatic side chains of amino acids in gas phase and solution

The vertical transition properties have been calculated for the valence electronic excited pipi* singlet states L-1(b), L-1(a), B-1(b), and B-1(a) of the chromophores benzene, phenol, and indole in bulk solvent. The polarizable continuum model was employed in the framework of a complete active space self-consistent reaction field with use of an atomic natural orbital basis set. Dynamical electron correlation was accounted for through the use of second-order multiconfigurational perturbation theory. The predicted solvatochromic shifts are compared with previous experimental and computational results. We find general agreement, in particular for the 1L(b) state of each species, where a red-shift is observed in bulk solvent. To our knowledge this is the first ab initio self-consistent reaction field study of the high-lying B-1(b) and B-1(a) states of benzene, phenol, and indole in bulk solvent. At the correlated level, the 1B(b) and 1B(a) states undergo red-shifts for benzene, shifts to the red and to the blue respectively for phenol, and shifts to the blue for indole.