Energy and Photoinduced Electron Transfer in Porphyrin−Fullerene Dyads

Abstract

Time-resolved fluorescence and absorption techniques have been used to investigate energy and photoinduced electron transfer in a covalently linked free-base porphyrin−fullerene dyad and its zinc analog. In toluene, the porphyrin first excited singlet states decay in about 20 ps by singlet−singlet energy transfer to the fullerene. The fullerene first excited singlet state is not quenched and undergoes intersystem crossing to the triplet, which exists in equilibrium with the porphyrin triplet state. In benzonitrile, photoinduced electron transfer from the porphyrin first excited singlet state to the fullerene competes with energy transfer. The fullerene excited singlet state is also quenched by electron transfer from the porphyrin. Overall, the charge-separated state is produced with a quantum yield approaching unity. This state lives for 290 ps in the free-base dyad and 50 ps in the zinc analog. These long lifetimes suggest that such dyads may be useful as components of more complex light-harvesting systems.

The effect of structural changes on charge transfer states in a light-harvesting carotenoid-diaryl-porphyrin-C60 molecular triad

“…[53][54][55][56][57][58][59][60] These considerations led to the synthesis of a CPC 60 molecular triad consisting of a diarylporphyrin (P) covalently linked to a carotenoid polyene (C) and a C 60 fullerene. 33 In natural photosynthetic systems, a high quantum yield of the final charge separated state is achieved through a series of short-range, fast, and efficient electron transfer transitions.…”

“…The excited state triplet radical pair recombines to yield a 3 C-P-C 60 triplet carotenoid state. 14 The main charge-transfer transition pathway between the ground-state and the final + CPC 60 -charge-separated state involves a local excitation on the porphyrin moiety, followed by electron transfer to the adjacent C 60 component. Next, the carotenoid transfers an electron to the positively charged porphyrin to yield the final charge-separated state.…”

“…61 The experimentally determined lifetime for the + CPC 60 -charge separated state is ~170 nanoseconds in a 2-methyltetrahydrofuran solution. 33 In 2003, Smirnov and coworkers employed a transient dc photocurrent technique to study transient dipoles formed upon excitation of the porphyrin chromophore in the CPC 60 triad. 62 The large magnitude (>150 D) of the experimentally determined dipole of the triad conforms to the particle-hole picture of the charge separated excited state, in which the hole state resides on the carotenoid component and the particle state is localized on the C 60 fullerene at a large particle-hole separation (>30 Å).…”

1,3-Dipolar cycloaddition of nitrile imines to meso-tetraarylporphyrins

“…TPP was used as fluorescence standard (λ exc = 532 nm) with Φ fl = 0.11 in toluene. 25 The fluorescence emission spectra of chlorins 4a-c in toluene are characterized by a strong emission band with a maximum intensity at 664.5 nm for chlorins 4a and 4b and at 662 nm for chlorin 4c (Figure 1 inset). The fluorescence quantum yields (Φ fl ) are summarized in Table 2; chlorin 4c showed the highest fluorescence quantum yield (Φ fl = 0.17).…”

Photobiocatalysis: The Power of Combining Photocatalysis and Enzymes

“…[30][31][32][33] Later, carbon nanotubes (CNTs) became available, representing a transition from molecular species (fulleroids) to materials. Also, CNTs have been widely used for photon induced electron transfer [34] and optoelectronic applications, including photovoltaic cells.…”