On the planarity of the tropolone molecule in the ù B² Aexcited state: A time dependent DFT geometry optimisation

Density functional theory along with the time-dependent formalism (TD-DFT) are used to directly localise the stationary points in the Ã1B2 first singlet excited state of tropolone. The optimisation reveals that the equilibrium geometry of tropolone in the excited state is planar, a result that seems in contradiction with recent analysis using the high-resolution degenerate four-wave mixing technique that finds a large inertial defect. A theoretical evaluation of the vibrational modes reveals the presence of a very small out-of-plane frequency that could also account for the observed large inertial defect. CASSCF and CASPT2 results validate the TD-DFT method to deal with excited intramolecular proton-transfer reactions. © 2005 Elsevier B.V. All rights reserved.