Linkage and Solvent Dependence of Photoinduced Electron Transfer in Zincporphyrin-C₆₀ Dyads

Abstract

Four different kinds of C60-linked zincporphyrins have been prepared by changing systematically the linking position at meso-phenyl ring from ortho to para and their photophysical properties have been investigated. Regardless of the linkage between the two chromophores, photoinduced charge separation (CS) and subsequent charge recombination (CR) were observed in a series of zincporphyrin-C60 dyads by picosecond fluorescence lifetime measurements and time-resolved transient absorption spectroscopy. In THF the CS occurs from both the excited singlet state of the porphyrin and the C60 moieties, implying that the increase of the absorption cross section by both the chromophores results in the efficient formation of the ion pair (IP) state. On the other hand, in benzene the IP state generated by the photoinduced CS from the excited singlet state of the porphyrin to the C60 produces or energetically equilibrates with the locally excited singlet state of the C60. Both the CS and CR rates for the meta isomer are much slower than those for the other porphyrin-linked C60. Linkage dependence of the electron transfer (ET) rates can be explained by superexchange mechanism via spacer. These results demonstrate that C60 is a new promising building block as an acceptor in artificial photosynthetic models.

Metal-chelating capacities attached to fullerenes

“…Similarly to 1, quenching of the excited porphyrin singlet state was observed, due to electron transfer from the excited porphyrin singlet state to the fullerene singlet state. The accepting properties of C 60 were compared with benzoquinone [13]. Accelerated charge separation and decelerated charge recombination were observed in 2 compared with the analogous C 60 -benzoquinone compound.…”

“…3). The covalent bond between the porphyrin phenyl group and the linker was varied from ortho (3), meta (4) to para (2 and 5) [14]. In addition, the cyclohexene ring fused to C 60 was also attached to the 2,3-position (5) on the aromatic spacer (3,4-position for 3 and 4).…”

Synthesis and electronic properties of donor-linked fullerenes

“…Actually, accelerated charge separation and 60 of many fullerene derivatives covalently bound to donor decelerated charge recombination has been observed in a moieties [5,6]. These systems provide entry into intrafullerene-based acceptor-donor system when compared to molecular processes such as energy and electron transfer the equivalent benzoquinone-based system [26]. This has been interpreted simply by the smaller reorganization energy (l) of C compared with those of small acceptors: the charge recombination rate downward in the inverted 38% yield.…”

Communication: Charge-transfer rate constants in zinc-porphyrin-porphyrin-derived dyads: A Fermi golden rule first-principles-based study

“…The hydrogenation is shown below to effectively tune the CT rates by determining the charge separation in the relevant electronic states, which in turn affects the key energetic parameters of the transfer process. 8,22 Porphyrin derivatives, in particular, are used as building blocks 30 for various optoelectronics applications and participate in functional CT processes in numerous biological systems. For example, the Zn-Bc-Bc dyad is found at the core of the magnesium-containing bacteriochlorophyll system.…”