Excited-State Intramolecular Protron Transfer: A Survey of TDDFT and RI-CC2 Excited-State Potential Energy Surfaces

Adelia J. A. Aquino*, Hans Lischka*
Institute for Theoretical Chemistry, Währingerstrasse 17, University of Vienna, A-1090 Vienna, Austria

Christof Hättig
Institute of Nanotechnology, Forschungszentrum Karlsruhe, P.O. Box 3640, D-76021 Karlsruhe, Germany

J. Phys. Chem. A 109, 3201-3208 (2005).
Received: January 17, 2005; In Final Form: February 12, 2005

TDDFT and RI-CC2 calculations have been performed on the excited-state intramolecular proton transfer in malonaldehyde, o-hydroxybenzaldehyde, salicylic acid, 7-hydroxy-1-indanone, and 2-(2'-hydroxyphenyl)benzothiazole. Vertical and adiabatic excitation energies have been computed for the n pi* and pi pi* states. Overall, we have found that both RI-CC2 and TDDFT methods are good candidates for the description of ESIPT potential energy surfaces. Proton transfer (PT) curves have been computed for both excited states. An essentially barrierless and very shallow energy profile has been found for the pi pi* state. For the n pi* state the keto minimum is more pronounced than for the pi pi* state and, depending on the case, energy barriers ranging from values < 0.1 eV up to 0.5 eV were found. From the computed PT curves we conclude that extended crossing regions between the two excited states will occur.

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