title: Electronically excited states and photochemical reaction mechanisms of β-glucose.
abstract: Carbohydrates are important molecular components of living matter. While spectroscopic and computational studies have been performed on carbohydrates in the electronic ground state, the lack of a chromophore complicates the elucidation of the excited-state properties and the photochemistry of this class of compounds. Herein, we report on the first computational investigation of the singlet photochemistry of β-glucose. It is shown that low-lying singlet excited states are of nσ* nature. Our computations of the singlet vertical excitation energies predict absorption from 6.0 eV onward. Owing to a dense manifold of weakly-absorbing states, a sizable and broad absorption in the ultraviolet-C range arises. We have explored two types of photochemical reaction mechanisms: hydrogen-detachment processes for each of the five O-H groups and a C-O ring-opening process. Both types of reactions are driven by repulsive nσ* states that are readily accessible from the Franck-Condon region and lead to conical intersections in a barrierless fashion. We have optimized the geometries of the conical intersections involved in these photochemical processes and found that these intersections are located around 5.0 eV for the O-H hydrogen-detachment reactions and around 4.0 eV for the C-O ring-opening reaction. The energies of all conical intersections are well below the computed absorption edge. The calculations were performed using linear-response methods for the computation of the vertical excitation energies and multiconfigurational methods for the optimization of conical intersections and the computation of energy profiles.
authors: Department of Chemistry, Technische Universität München, 85747 Garching, Germany. deniz.tuna@ch.tum.de.
authors: Deniz
authors: D
authors: Tuna
authors: Andrzej L
authors: AL
authors: Sobolewski
authors: Wolfgang
authors: W
authors: Domcke
mesh_terms: D000042:Absorption; D002236:Carbohydrate Conformation; D004583:Electrons; D005947:Glucose / Q000737:chemistry*; D006859:Hydrogen / Q000737:chemistry; D008958:Models, Molecular; D055668:Photochemical Processes; D011789:Quantum Theory
chemical_list: D006859:Hydrogen; D005947:Glucose