title: Ultrafast photoinduced electron transfer in directly linked porphyrin-ferrocene dyads.
abstract: The ultrafast electron transfer occurring upon Soret excitation of three new porphyrin-ferrocene (XP-Fc) dyads has been studied by femtosecond up-conversion and pump-probe techniques. In the XP-Fc dyads (XP-Fcs) designed in this study, the ferrocene moiety is covalently bonded to the meso positions of 3,5-di-tert-butylphenyl zinc porphyrin (BPZnP-Fc), pentafluorophenyl zinc porphyrin (FPZnP-Fc), and 3,5-di-tert-butylphenyl free-base porphyrin (BPH2P-Fc). Charge separation and recombination in the XP-Fcs were confirmed by transient absorption spectra, and the lifetimes of the charge-separated states were estimated from the decay rate of the porphyrin radical anion band to be approximately 20 ps. The charge-separation rates of the XP-Fcs were found to be >10(13) s-1 from the S2 state and 6.3x10(12) s-1 from the S1 state. Charge separation from the S2 state was particularly efficient for BPZnP-Fc, whereas the main reaction pathway was from the S1 state for BPH2P-Fc. Charge separation from the S2 and S1 states occurred at virtually the same rate in benzene and tetrahydrofuran and was much faster than their solvation times. Analysis of these results using semiquantum Marcus theory indicates that the magnitude of the electronic-tunneling matrix element is rather large and far outside the range of nonadiabatic approximation. The pump-probe data show the presence of vibrational coherence during the reactions, suggesting that wavepacket dynamics on the adiabatic potential energy surface might regulate the ultrafast reactions.
authors.affiliation: Department of Materials Engineering Science, Graduate School of Engineering Science, Osaka University, Toyonaka 560-8531, Japan. M.Kubo@neu.edu
authors.forename: Minoru
authors.initials: M
authors.lastname: Kubo
authors.forename: Yukie
authors.initials: Y
authors.lastname: Mori
authors.forename: Masana
authors.initials: M
authors.lastname: Otani
authors.forename: Masataka
authors.initials: M
authors.lastname: Murakami
authors.forename: Yukihide
authors.initials: Y
authors.lastname: Ishibashi
authors.forename: Masakazu
authors.initials: M
authors.lastname: Yasuda
authors.forename: Kohei
authors.initials: K
authors.lastname: Hosomizu
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Miyasaka
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Imahori
authors.forename: Satoru
authors.initials: S
authors.lastname: Nakashima
mesh_terms: D004583:Electrons; D005296:Ferrous Compounds / Q000737:chemistry* / Q000378:metabolism; D000075163:Metallocenes; D015394:Molecular Structure; D010777:Photochemistry; D011166:Porphyrins / Q000737:chemistry* / Q000378:metabolism; D013816:Thermodynamics; D013997:Time Factors
chemical_list: D005296:Ferrous Compounds; D000075163:Metallocenes; D011166:Porphyrins; C004998:ferrocene