Studies on Intra-Supramolecular and Intermolecular Electron-Transfer Processes between Zinc Naphthalocyanine and Imidazole-Appended Fullerene

• Published in: Chemphyschem Vol. 4; no. 5; pp. 474 - 481
• Main Authors: El-Khouly, Mohamed E., Rogers, Lisa M., Zandler, Melvin E., Suresh, Gadde, Fujitsuka, Mamoru, Ito, Osamu, D'Souza, Francis
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 14-04-2003; WILEY‐VCH Verlag; Wiley
• Subjects: Chemistry; Electrochemistry; electron transfer; Electron Transport; Exact sciences and technology; Fluorescence; fullerenes; Fullerenes - chemistry; General and physical chemistry; Imidazoles - chemistry; Models, Molecular; Molecular Structure; Organometallic Compounds - chemistry; Photochemistry; phthalocyanines; Physical chemistry of induced reactions (with radiations, particles and ultrasonics); radical ions; Solvents - chemistry; Spectrophotometry, Ultraviolet; supramolecular chemistry; Time Factors; Zinc Compounds - chemistry; radical ions; Nitrogen heterocycle; Organic ligand; Electron transfer; Transition metal Complexes; Photochemical reaction; Macrocycle; Cyclic voltammetry; phthalocyanines; Metallophthalocyanine; Imidazole; Supramolecular structure; Fullerenes; Zinc Complexes; supramolecular chemistry
• ISSN: 1439-4235; 1439-7641
• DOI: 10.1002/cphc.200200540

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 1.4×1010 s−1 and 5.3×107 s−1 in toluene and 8.9×109 s−1 and 9.2×107 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 5.3×108 M−1 s−1.
An unpaired pair: Efficient, photoinduced electron transfer in a complex bearing an imidazole coordinating entity (see picture), which is self‐assembled by axial coordination of zinc naphthalocyanine and fulleropyrrolidine, is reported. The optical absorption, singlet emission, and electrochemical studies, as well as ab initio B3 LYP/3–21G(*) calculations revealed stable complex formation. Direct evidence for radical ion‐pair formation in the dyad was obtained from picosecond transient‐absorption studies.