Photoinduced Electron Transfer in Phytochlorin−[60]Fullerene Dyads

Abstract

Novel molecular electron donor-acceptor (DA) dyads, composed of a phytochlorin donor and a [60]fullerene acceptor, have been photochemically characterized. In these dyads, a pyrrolidine spacer group links the chlorin and the C 60 moieties covalently, forming a rigid dyad with a short and almost constant D-A distance. The photochemical behavior of the metal-free dyads and the corresponding Zn complexes was studied by means of fluorescence and absorption spectroscopies with femto-and picosecond time resolutions in polar benzonitrile and nonpolar toluene solutions. In consistence with the previous studies on porphyrin-fullerene dyads, the novel chlorin-fullerene dyads underwent a fast intramolecular photoinduced electron transfer in a benzonitrile solution. The recombination rates of the charge-transfer (CT) states were 4.8 × 10 10 s -1 for the Zn dyads and ca. 1.5 × 10 10 s -1 for the metal-free compounds. The CT state was preceded by at least three intermediate states in the time domain from 200 fs to 100 ps. Two of the states were identified as singlet excited states of either the phytochlorin or the fullerene moiety. The third state was attributed to an intramolecular exciplex, which was transformed to the CT state. In the frame of this model, the formation rate constant of the CT state was estimated to be 1.6 × 10 11 s -1 for the Zn dyads and 0.5 × 10 11 s -1 for the metal-free compounds. The formation of the exciplex was also observed in nonpolar solvents, e.g., toluene. In contrast to the behavior in polar solvents, the exciplex relaxed in toluene directly to the ground state, without the formation of the CT state. The lifetime of the exciplex was 140 ps for the Zn dyads and 1-2 ns for the metal-free compounds in toluene.

Metal-chelating capacities attached to fullerenes

“…For dyads 29 and 30, synthesized by Diels Alder and Prato reaction, quenching of the photoinduced chlorine excited states was observed [37,38]. Time-resolved fluorescence and absorption spectroscopy revealed that an intramolecular exciplex was formed upon photoexcitation of the chlorine moiety of 30 [39]. Such an exciplex was not detected for analogous C 60 -porphyrin dyads.…”

Synthesis, Conformational Interconversion, and Photophysics of Tethered Porphyrin–Fullerene Dyads with Parachute Topology

“…The instrumentation and the data analysis procedure have been described earlier. [20,21] 2-(3-Hydroxypropoxy)benzaldehyde: Potassium hydroxide (3.8 g, 56.3 mmol, 85 % purity) was dissolved in EtOH (60 mL). The flask was attached to a reflux condenser with a rubber septum on top and purged with nitrogen.…”

Photoinduced Electron Transfer of Dialkynyldisilane-Linked Zinc Porphyrin–[60]Fullerene Dyad

“…The present decay sequences are qualitatively consistent with those determined for other porphyrin-fullerene dyads. 14,18,38 Conclusion A novel zinc porphyrin-fullerene dyad covalently connected by a disilane bridge (ZnP-Si 2 -C 60 ) was synthesized and fully identified by its 1 H, 13 C, and 29 Si NMR and FAB mass spectra. The quenching paths from 1 ZnP Ã -Si 2 -C 60 are most probably attributed to the charge separation in polar solvents.…”