title: Studies on intra-supramolecular and intermolecular electron-transfer processes between zinc naphthalocyanine and imidazole-appended fullerene.
abstract: Spectroscopic, computational, redox, and photochemical behavior of a self-assembled donor-acceptor dyad formed by axial coordination of zinc naphthalocyanine, ZnNc, and fulleropyrrolidine bearing an imidazole coordinating ligand (2-(4'-imidazolylphenyl)-fulleropyrrolidine, C60Im) was investigated in noncoordinating solvents, toluene and o-dichlorobenzene, and the results were compared to the intermolecular electron transfer processes in a coordinating solvent, benzonitrile. The optical absorption and ab initio B3 LYP/3-21G(*) computational studies revealed self-assembled supramolecular 1:1 dyad formation between the ZnNc and C60Im entities. In the optimized structure, the HOMO was found to be entirely located on the ZnNc entity while the LUMO was found to be entirely on the fullerene entity. Cyclic voltammetry studies of the dyad exhibited a total of seven one-electron redox processes in o-dichlorobenzene, with 0.1 M tetrabutylammonium perchlorate. The excited-state electron-transfer processes were monitored by both optical-emission and transient-absorption techniques. Direct evidence for the radical-ion-pair (C60Im.-:ZnNC.+) formation was obtained from picosecond transient-absorption spectral studies, which indicated charge separation from the singlet-excited ZnNc to the C60Im moiety. The calculated rates of charge separation and charge recombination were 1.4 x 10(10) s-1 and 5.3 x 10(7) s-1 in toluene and 8.9 x 10(9) s-1 and 9.2 x 10(7) s-1 in o-dichlorobenzene, respectively. In benzonitrile, intermolecular electron transfer from the excited triplet state of ZnNc to C60Im occurs and the second-order rate constant (kqtriplet) for this quenching process was 5.3 x 10(8)M-1s-1.
authors.affiliation: Institute of Multidisciplinary Research for Advanced Materials Tohoku University, CREST, JST, Katahira, Sendai, 980-8577, Japan.
authors.forename: Mohamed E
authors.initials: ME
authors.lastname: el-Khouly
authors.forename: Lisa M
authors.initials: LM
authors.lastname: Rogers
authors.forename: Melvin E
authors.initials: ME
authors.lastname: Zandler
authors.forename: Gadde
authors.initials: G
authors.lastname: Suresh
authors.forename: Mamoru
authors.initials: M
authors.lastname: Fujitsuka
authors.forename: Osamu
authors.initials: O
authors.lastname: Ito
authors.forename: Francis
authors.initials: F
authors.lastname: D'Souza
mesh_terms: D004563:Electrochemistry; D004579:Electron Transport; D005453:Fluorescence; D037741:Fullerenes / Q000737:chemistry*; D007093:Imidazoles / Q000737:chemistry*; D008958:Models, Molecular; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000737:chemistry*; D012997:Solvents / Q000737:chemistry; D013056:Spectrophotometry, Ultraviolet; D013997:Time Factors; D017967:Zinc Compounds / Q000737:chemistry*
chemical_list: D037741:Fullerenes; D007093:Imidazoles; D009942:Organometallic Compounds; D012997:Solvents; D017967:Zinc Compounds; C483615:zinc naphthalocyanine; C029899:imidazole; C069837:fullerene C60