Stabilization of charge-separated states in phthalocyanine-fullerene ensembles through supramolecular donor-acceptor interactions

A novel ZnPC-C-60 dyad (3), in which two photoactive units are brought together by a phenylenevinylene spacer has been synthesized. The synthetic strategy en route toward 3 involves a Heck reaction to attach 4-vinylbenzaldehyde to a monoioclophthalocyanine precursor, followed by standard cycloaddition of azomethine ylides (generated from the formylPc derivative and N-methylglycine) to one of the double bonds of C-60. Electrochemical studies reveal that in 3 the ZnPc is about 39 mV more difficult to oxidize than in the corresponding ZnPc, reference, which points to appreciable electronic communication between ZnPc and C-60 in the ground state. In the excited state, photoexcitation leads to the formation of a charge-separated ZnPC.+-C-60(.-) state, for which a lifetime of 130 ns was determined in THF. Hetero-association between complementary PCs (1 and 2 or 3 and 2), which carry different peripheral functionalities (i.e., either electron-donating alkoxy groups or electron-deficient alkylsulfonyl chains) was assessed by different techniques. They provided evidence for donor-acceptor 1:1 complex formation with a stability constant of ca. 10(5) M-1 in CHCl3. Interestingly, hetero-association of ZnPC-C-60 dyad 3 with an electrondeficient PdPc (2) allowed the construction of supramolecular triads, in which a substantial stabilization of the radical pair is seen relative to that of the covalently linked dyad ZnPC-C-60 (3).