TY - JOUR
T1 - Photophysics of intramolecularly hydrogen-bonded aromatic systems
T2 - Ab initio exploration of the excited-state deactivation mechanisms of salicylic acid
AU - Sobolewski, Andrzej L.
AU - Domcke, Wolfgang
PY - 2006
Y1 - 2006
N2 - Excited state reaction paths and the corresponding energy profiles of salicylic acid have been determined with the CC2 method, which is a simplified version of singles-and-doubles coupled cluster theory. At crucial points of the potential energy hypersurfaces, single-point energy calculations have been performed with the CASPT2 method (second-order perturbation theory based on the complete active space self-consistent field reference). Hydrogen transfer along the intramolecular hydrogen bond as well as torsion and pyramidization of the carboxy group have been identified as the most relevant photochemical reaction coordinates. The keto-type planar S1 state reached by barrierless intramolecular hydrogen transfer represents a local minimum of the S1 energy surface, which is separated by a very low barrier from a reaction path leading to a low-lying S1-S0 conical intersection via torsion and pyramidization of the carboxy group. The S1-S0 conical intersection, which occurs for perpendicular geometry of the carboxy group, is a pure biradical. From the conical intersection, a barrierless reaction path steers the system back to the two known minima of the S 0 potential energy surface (rotamer I, rotamer II). A novel structure, 7-oxa-bicyclo[4.2.0]octa-1(6),2,4-triene-8,8-diol, has been identified as a possible transient intermediate in the photophysics of salicylic acid.
AB - Excited state reaction paths and the corresponding energy profiles of salicylic acid have been determined with the CC2 method, which is a simplified version of singles-and-doubles coupled cluster theory. At crucial points of the potential energy hypersurfaces, single-point energy calculations have been performed with the CASPT2 method (second-order perturbation theory based on the complete active space self-consistent field reference). Hydrogen transfer along the intramolecular hydrogen bond as well as torsion and pyramidization of the carboxy group have been identified as the most relevant photochemical reaction coordinates. The keto-type planar S1 state reached by barrierless intramolecular hydrogen transfer represents a local minimum of the S1 energy surface, which is separated by a very low barrier from a reaction path leading to a low-lying S1-S0 conical intersection via torsion and pyramidization of the carboxy group. The S1-S0 conical intersection, which occurs for perpendicular geometry of the carboxy group, is a pure biradical. From the conical intersection, a barrierless reaction path steers the system back to the two known minima of the S 0 potential energy surface (rotamer I, rotamer II). A novel structure, 7-oxa-bicyclo[4.2.0]octa-1(6),2,4-triene-8,8-diol, has been identified as a possible transient intermediate in the photophysics of salicylic acid.
UR - http://www.scopus.com/inward/record.url?scp=33746174164&partnerID=8YFLogxK
U2 - 10.1039/b604610j
DO - 10.1039/b604610j
M3 - Article
C2 - 16855719
AN - SCOPUS:33746174164
SN - 1463-9076
VL - 8
SP - 3410
EP - 3417
JO - Physical Chemistry Chemical Physics
JF - Physical Chemistry Chemical Physics
IS - 29
ER -