Theoretical investigations of electronic structure and tautomerism in ground and excited states of 1-[N-(4-fluorophenyl)]naphthaldimine

Electronic structure of 1-[N-(4-Fluorophenyl)]naphthaldiinine phenol-imine (1) and quinoid (2) tautomers in ground and excited states are presented. The density functional calculations predict the ground state of I to be 5.4 kJ mol(-1) lower in energy owing to stronger 0-H...N (1.638 angstrom) interactions relative to O...H-N (1.651 angstrom) interactions in 2. The influence of solvents on the tautomeric stability as revealed from the self-consistent reaction field (SCRF) calculations suggests tautomer 2 to be of lower energy in protic polar solvents. Time-dependent density functional (TDDFT) calculations on the other hand bring about the reversal of relative stabilization and facilitate the tautomer 2 to be 6.6 kJ mol(-1) lower in energy in the lowest excited state which results from the extended conjugation owing to its planar geometry. (c) 2006 Elsevier B.V. All rights reserved.