A supramolecular Star Wars Tie Fighter Ship:: electron transfer in a self-assembled triad composed of two zinc naphthalocyanines and a fullerene

Photoactive supramolecules composed of electron donor and electron acceptor entities are important for light energy harvesting applications. In the present study, a Star Wars Tie Fighter Ship shaped supramolecular triad was constructed by self-assembling two zinc naphthalocyanines to a fulleropyrrolidine bearing two pyridine entities using an axial coordination approach. Optical absorption and emission studies revealed stable complex formation, and the experimentally determined free-energy change revealed the possibility of electron transfer from singlet excited zinc naphthalocyanine to the fulleropyrrolidine. The picosecond time-resolved emission technique was utilized to evaluate the kinetics of charge separation while nanosecond transient absorption spectral studies provided evidence for electron transfer quenching. The measured charge-separation rate, k(CS) and quantum yield, Phi(CS) were found to be 5.7 x 10(9) s(-1) and 0.93 in toluene, respectively, indicating an efficient process within the supramolecular triad. The charge recombination rate (k(CR)) of the supramolecular ion-pair calculated from the nanosecond transient absorption technique was found to be 3.5 x 10(7) s(-1) yielding a lifetime for the radical ion-pair (tau(RIP)) of about 30 ns. Changing the solvent from the noncoordinating toluene to the coordinating benzonitrile or THF destroyed the supramolecular structure, and under these experimental conditions, only intermolecular electron transfer from the triplet excited zinc naphthalocyanine to fulleropyrrolidine could be observed. Under these conditions, the measured electron transfer rates, k(et,T)(inter), were found to be 2.6 x 10(7) M-1.s(-1) in benzonitrile and 1.2 x 10(7) M-1.s(-1) in THF, respectively. Copyright (C) 2005 Society of Porphyrins & Phthalocyanines.