Energy transfer in ethane-bisporphyrin dimers studied by fluorescence line narrowing and spectral hole burning

Abstract

The quasi-line fluorescence excitation spectrum of 1,2-bis (2,3,7,8,12,13,17,18-octaethyl-21H,23 H-porphino) ethane at 4.8 K consists of two subbands with the splitting mean value of 51cm-', that are ascribed to the donor and the acceptor half of the homodimer. The donor's fluorescence is quenched by an efficient energy transfer to the acceptor. The energy transfer rate of 10" s-l, determined by spectral hole burning, has been compared with the calculated value and a conclusion of nonconsistency with the Forster energy transfer mechanism has been drawn.

Deactivation of Excited States in Nanostructures Containing Cu-Porphyrin Subunit

“…[62][63][64][65][66][67] The same basic conclusions have been derived for homodimers with phenyl spacer, (OEP) 2 Ph or (ZnOEP) 2 Ph.…”

“…Stepanov Institute of Physics, National Academy of Sciences of Belarus (Minsk) and described in details together with their optical properties in our earlier publications. In this paper, the subject of the discussion will be the dimers in which tetrapyrrolic subunits are covalently linked via spacers of various nature: i) ethane-bisporphyrins with a single -CH 2 -CH 2 -via meso-positions, [34,[61][62][63][64][65][66][67] ii) cyclodimers where cyclopentaneporphyrin molecules are coupled via isocycles, [68][69][70][71][72][73] and iii) chemical dimers of octaethylporphyrins with the phenyl bridge via meso-positions. [17,18,27,[74][75][76] It should be noted that in order to clarify spectral-kinetic properties that are characteristic for the dimers namely, we have especially prepared and characterized the precursor monomeric species with side substituents of the same nature and in the same positions like the corresponding spacers.…”

“…Heterodimers containing a Cu ion in the center of one subunit have some general features. [62][63][64][65][66][67][68][69][70] In the case of the heterodimers (H 2 P+Cu)(OEP) 2 and (Zn+Cu)(OPP) 2 the emission belongs to the H 2 -or Zn-subunit, but is drastically quenched (j/ j 0 ≈40, Table 1). The singlet-singlet ET from Cu-subunit to H 2 -or Zn-subunit having a S 0 -S 1 transitions is not detected, and, additionally, the lifetime of the T 1 state (t T ) of H 2 -or Zn-subunits is decreased in these heterodimers compared to the corresponding homodimers without Cu-porphyrins.…”

Oligoporphyrins with One-and Two-Atom Covalent Bridges: Synthesis and Reactivity, Solid-State, Solution and Electronic Structures, Spectroscopy and Applications

“…The interpretation of these results and the hole-burning was that fluorescence of the homodimer results from both localized emission and intradimer ET. 153 Borovkov et al also reported the emission spectra of the heterodimers containing Mn(III) and Fe(III), and attributed the pronounced fluorescence quenching to energetically favored intramolecular electron transfer from the S 1 state of the Zn or H 2 sub-unit to the Mn or Fe moiety. The syn conformation of 18o leads to a significant red-shift of the emission bands compared with those of the anti-disposed 18p and 18s.…”

“…149 Moreover, singlet oxygen generation through the triplet excited states of the free base and zinc dimers was found to be efficient, while the presence of Ni(II) in one or both rings prevented singlet oxygen sensitization due to the very fast deactivation of the singlet excited state. 151,152 The most sophisticated experiments reported by Mauring et al in 1995 153 and reviewed in 1999, 154 involved fluorescence line-narrowing and spectral hole-burning at 1.8-10 K for bis(free base) 18b, model monomer 5-methylH 2 OEP, and the H 2 /Cu heterodimer 18i. Vibronic structure of the fluorescence emission in THF/toluene glass was clearly revealed by selective excitation into the 0-0 absorption band of 18b, and this was virtually identical to that for the monomer model.…”