title: Synthesis and Photophysical Properties of Two Diazaporphyrin-Porphyrin Hetero Dimers in Polar and Nonpolar Solutions.
abstract: Two diazaporphyrin (DAP)-porphyrin hetero dimers, in β-meso and β-β configurations, were prepared to study their photoinduced intramolecular electron transfer properties. The two meso nitrogen atoms in the porphyrin ring of DAP change its redox potential, making DAP more easily reduced, compared to its porphyrin counterpart. A charge-transfer from porphyrin to DAP in both hetero dimers was verified by versatile optical spectroscopic methods. The steady-state fluorescence spectra indicated an efficient intramolecular exciplex formation for both dimers. For the β-meso dimer, ultrafast time-resolved spectroscopic methods revealed the subpicosecond formation of two types of primary short-living (1-18 ps) intramolecular exciplexes, which relaxed in toluene to form a long-living final exciplex (1.4 ns) followed by a longer-living charge transfer complex (>5 ns). However, in benzonitrile, the lifetime of the final exciplex was longer (660 ps) as was that of the charge transfer complex (180 ps). The β-β analogue formed similar short-living exciplexes in both solvents, but the final exciplex and the charge transfer state had significantly shorter lifetimes. The electrochemical redox potential measurements and density functional theory calculations supported the proposed mechanism.
authors.affiliation: †Department of Chemistry and Bioengineering, Tampere University of Technology, P.O. Box 540, 33101 Tampere, Finland.
authors.forename: Fawzi
authors.initials: F
authors.lastname: Abou-Chahine
authors.forename: Daisuke
authors.initials: D
authors.lastname: Fujii
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Imahori
authors.affiliation: ∥Department of Chemistry, Graduate School of Sciences, Kyushu University, Fukuoka 812-8581, Japan.
authors.forename: Haruyuki
authors.initials: H
authors.lastname: Nakano
authors.affiliation: †Department of Chemistry and Bioengineering, Tampere University of Technology, P.O. Box 540, 33101 Tampere, Finland.
authors.forename: Nikolai V
authors.initials: NV
authors.lastname: Tkachenko
authors.affiliation: ⊥Department of Chemistry, Faculty of Science, Niigata University, Niigata 950-2181, Japan.
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Matano
authors.affiliation: †Department of Chemistry and Bioengineering, Tampere University of Technology, P.O. Box 540, 33101 Tampere, Finland.
authors.forename: Helge
authors.initials: H
authors.lastname: Lemmetyinen