title: Design and studies on supramolecular ferrocene-porphyrin-fullerene constructs for generating long-lived charge separated states.
abstract: Supramolecular ferrocene-porphyrin-fullerene constructs, in which covalently linked ferrocene-porphyrin-crown ether compounds were self-assembled with alkylammonium cation functionalized fullerenes, have been designed to achieve stepwise electron transfer and hole shift to generate long-lived charge separated states. The adopted crown ether-alkylammonium cation binding strategy resulted in stable conjugates as revealed by computational studies performed by the DFT B3LYP/3-21G(*) method in addition to the binding constants obtained from fluorescence quenching studies. The free-energy changes for charge-separation and charge-recombination were varied by the choice of different metal ions in the porphyrin cavity. Free-energy calculations suggested that the light-induced electron-transfer processes from the singlet excited state of porphyrins to be exothermic in all of the investigated supramolecular dyads and triads. Photoinduced charge-separation and charge-recombination processes have been confirmed by the combination of the time-resolved fluorescence and nanosecond transient absorption spectral measurements. In case of the triads, the charge-recombination processes of the radical anion of the fullerene moiety take place in two steps, viz., a direct charge recombination from the porphyrin cation radical and a slower step involving distant charge recombination from the ferrocene cation moiety. The rates of charge recombination for the second route were found to be an order of magnitude slower than the former route, thus fulfilling the condition for charge migration to generate long-lived charge-separated states in supramolecular systems.
authors.affiliation: Department of Chemistry, Wichita State University, Wichita, Kansas 67260-0051, USA. Francis.DSouza@wichita.edu
authors.forename: Francis
authors.initials: F
authors.lastname: D'Souza
authors.forename: Raghu
authors.initials: R
authors.lastname: Chitta
authors.forename: Suresh
authors.initials: S
authors.lastname: Gadde
authors.forename: D-M Shafiqul
authors.initials: DM
authors.lastname: Islam
authors.forename: Amy L
authors.initials: AL
authors.lastname: Schumacher
authors.forename: Melvin E
authors.initials: ME
authors.lastname: Zandler
authors.forename: Yasuyuki
authors.initials: Y
authors.lastname: Araki
authors.forename: Osamu
authors.initials: O
authors.lastname: Ito
mesh_terms: D002412:Cations / Q000737:chemistry; D043844:Crown Ethers / Q000737:chemistry; D004583:Electrons; D005296:Ferrous Compounds / Q000737:chemistry*; D037741:Fullerenes / Q000737:chemistry*; D046911:Macromolecular Substances / Q000138:chemical synthesis / Q000737:chemistry; D000075163:Metallocenes; D008956:Models, Chemical; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D011166:Porphyrins / Q000737:chemistry*; D000644:Quaternary Ammonium Compounds / Q000737:chemistry
chemical_list: D002412:Cations; D043844:Crown Ethers; D005296:Ferrous Compounds; D037741:Fullerenes; D046911:Macromolecular Substances; D000075163:Metallocenes; D009942:Organometallic Compounds; D011166:Porphyrins; D000644:Quaternary Ammonium Compounds; C004998:ferrocene