Efficient Charge Separation in Porphyrin-Fullerene-Ligand Complexes

Photoprocesses associated with the complexation of a pyridine‐functionalized C60 fullerene derivative to ruthenium‐ and zinc‐tetraphenylporphyrins (tpp) have been studied by time‐resolved optical and transient EPR spectroscopies. It has been found that upon irradiation in toluene, a highly efficient triplet–triplet energy transfer governs the deactivation of the photoexcited [Ru(tpp)], while electron transfer (ET) from the porphyrin to the fullerene prevails in polar solvents. Complexation of [Zn(tpp)] by the fullerene derivative is reversible and, following excitation of the [Zn(tpp)], gives rise to very efficient charge separation. In fluid polar solvents such as THF and benzonitrile, radical‐ion pairs (RPs) are generated both by intramolecular ET inside the complex and by intermolecular ET in the uncomplexed form. Charge‐separated states have lifetimes of about 10 μs in THF and several hundred of microseconds in benzonitrile at room temperature. In questo lavoro viene riportato il comportamento fotoindotto di due diadi, ottenute attraverso coordinazione di un derivato fullerenico contenente un frammento piridinico a una rutenio o a una zinco tetrafenilporfirina. I processi sono stati studiati mediante due diverse spettroscopie risolte nel tempo: ottica ed EPR. Mentre in toluene, in seguito a irraggiamento, si osserva il trasferimento di energia dalla porfirina al fullerene, in solventi più polari prevale il trasferimento elettronico. Nel caso della [Zn(tpp)] dallo stato eccitato si ottiene un'efficiente separazione di carica sia in processi intramolecolari (nella forma complessata) che in processi intermolecolari (nella forma non complessata). Per la [Zn(tpp)], i tempi di vita delle coppie ioniche generate sono notevoli, alcuni microsecondi in THF e diverse centinaia di microsecondi in benzonitrile a temperatura ambiente. Interesting supramolecular assemblies are produced through the complexation of a pyridine‐fullerene derivative to metal porphyrins (an example is shown here). Excitation of the porphyrin chromophore in polar solvents is followed by rapid electron transfer to the fullerene unit. Equilibrium between the chromophores is responsible for very long lifetimes of the charge‐separated species.