title: Role of noncoplanar conformation in facilitating ground state hole transfer in oxidized porphyrin dyads.
abstract: We employ density functional theory to investigate ground state hole transfer in covalently linked oxidized zinc-zinc porphyrin ([ZnZn](+)) and zinc-free-base porphyrin ([ZnFb](+)) dyads in both coplanar and noncoplanar (tilted) conformations. We obtain reactant, product, and transition state (TS) for the hole transfer reaction in the [ZnZn](+) system. The hole is localized on a single porphyrin unit in the reactant and product states while delocalized in the TS, implying the dominance of superexchange mechanism in the hole transfer reaction. A metastable as well as stable states are located for the [ZnFb](+) system while no TS is found, indicating a barrierless hole transfer reaction. The hole lifetimes are calculated to be 15.80 and 0.034 ns for [ZnZn](+) in the coplanar and tilted conformation, respectively, and 14.45 and 0.313 ns for [ZnFb](+). The hole transfer rates are found to be several orders of magnitude faster in the tilted conformation than in the coplanar conformation for both dyads, showing the importance of noncoplanar conformation between the two porphyrin pigments in facilitating the hole transfer process. We also show that inclusion of solvent effects in calculations plays an important role in the proper ground state hole localization in oxidized dyads. These results provide an unconventional insight into the hole transfer mechanism in porphyrin arrays and are relevant to design of artificial photoharvesting materials.
authors.affiliation: Department of Chemistry, North Carolina State University, Raleigh, North Carolina 27695, USA.
authors.forename: Takashi
authors.initials: T
authors.lastname: Tsuchiya
authors.forename: Elena
authors.initials: E
authors.lastname: Jakubikova
mesh_terms: D008968:Molecular Conformation; D010084:Oxidation-Reduction; D011166:Porphyrins / Q000737:chemistry*; D011789:Quantum Theory
chemical_list: D011166:Porphyrins