title: Photosynthetic reaction center mimicry: low reorganization energy driven charge stabilization in self-assembled cofacial zinc phthalocyanine dimer-fullerene conjugate.
abstract: By employing well-defined self-assembly methods, a biomimetic bacterial photosynthetic reaction center complex has been constructed, and photoinduced electron transfer originating in this supramolecular donor-acceptor conjugate has been investigated. The biomimetic model of the bacterial "special pair" donor, a cofacial zinc phthalocyanine dimer, was formed via potassium ion induced dimerization of 4,5,4',5',4'', 5'',4''',5'''-zinc tetrakis(1,4,7,10,13-pentaoxatridecamethylene)phthalocyanine. The dimer was subsequently self-assembled with functionalized fullerenes via "two-point" binding involving axial coordination and crown ether-alkyl ammonium cation complexation to form the donor-acceptor pair, mimicking the noncovalently bound entities of the bacterial photosynthetic reaction center. The adopted self-assembly methodology yielded a supramolecular complex of higher stability with defined geometry and orientation as revealed by the binding constant and computational optimized structure. Unlike the previously reported porphyrin analog, the present phthalocyanine macrocycle based model system exhibited superior electron-transfer properties including formation of a long-lived charge-separated state, a key step of the photosynthetic light energy conversion process. Detailed analysis of the kinetic data in light of the Marcus theory of electron transfer revealed that small reorganization energy of the relatively rigid phthalocyanine is primarily responsible for slower charge-recombination process. The importance of the cofacial dimer in stabilizing the charge-separated state is borne out in the present all-supramolecular "reaction center" donor-acceptor mimic.
authors.affiliation: Department of Chemistry, Wichita State University, 1845 Fairmount, Wichita, Kansas 67260-0051, USA. francis.dsouza@wichita.edu
authors.forename: Francis
authors.initials: F
authors.lastname: D'Souza
authors.forename: Eranda
authors.initials: E
authors.lastname: Maligaspe
authors.forename: Kei
authors.initials: K
authors.lastname: Ohkubo
authors.forename: Melvin E
authors.initials: ME
authors.lastname: Zandler
authors.forename: Navaneetha K
authors.initials: NK
authors.lastname: Subbaiyan
authors.forename: Shunichi
authors.initials: S
authors.lastname: Fukuzumi
mesh_terms: D001419:Bacteria / Q000737:chemistry* / Q000378:metabolism; D032701:Biomimetics; D003198:Computer Simulation; D019281:Dimerization; D004563:Electrochemistry; D004579:Electron Transport; D037741:Fullerenes / Q000737:chemistry*; D007211:Indoles / Q000737:chemistry*; D054833:Isoindoles; D009682:Magnetic Resonance Spectroscopy; D008954:Models, Biological; D008958:Models, Molecular; D009942:Organometallic Compounds / Q000737:chemistry*; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry* / Q000378:metabolism; D011789:Quantum Theory; D013050:Spectrometry, Fluorescence; D013056:Spectrophotometry, Ultraviolet; D017967:Zinc Compounds
chemical_list: D037741:Fullerenes; D007211:Indoles; D054833:Isoindoles; D009942:Organometallic Compounds; D045322:Photosynthetic Reaction Center Complex Proteins; D017967:Zinc Compounds; C052159:Zn(II)-phthalocyanine