A zinc(ii) phthalocyanine-tin(iv) porphyrin dyad with a strong electronic coupling was synthesized and upon light excitation shown to exhibit ultra-fast, long-range electron transfer in a single step.

The synthesis and photophysical characterization of two sets of zinc porphyrin platinum acetylide complexes are reported. The two sets of molecules differ in the way the bridging phenyl-ethynyl unit is attached to the porphyrin ring. One set is attached via an ethynyl unit on the beta position, while the other set is attached via a phenyl unit on the meso position of the porphyrin. These were compared with previously studied complexes where attachment was made via an ethynyl unit on the meso position. Femtosecond transient absorption measurements showed in all systems a rapid quenching of the porphyrin singlet state. Electron transfer is suggested as the quenching mechanism, followed by an even faster recombination to form both the porphyrin ground and triplet excited states. This is supported by the variation in quenching rate and porphyrin triplet yield with solvent polarity, and the observation of an intermediate state in the meso-phenyl linked systems. The different linking motifs between the dyads resulted in significant variations in electron transfer rates.

In the context of long-range electron transfer for solar energy conversion, we present the synthesis, photophysical, and computational characterization of two new zinc(II) phthalocyanine oligophenylene-ethynylene based donor-bride-acceptor dyads: ZnPc-OPE-AuP⁺ and ZnPc-OPE-C₆₀. A gold(III) porphyrin and a fullerene has been used as electron accepting moieties, and the results have been compared to a previously reported dyad with a tin(IV) dichloride porphyrin as the electron acceptor (Fortage et al. Chem. Commun.2007, 4629). The results for ZnPc-OPE-AuP⁺ indicate a remarkably strong electronic coupling over a distance of more than 3 nm. The electronic coupling is manifested in both the absorption spectrum and an ultrafast rate for photoinduced electron transfer (k_PET = 1.0 × 10¹² s^–1). The charge-shifted state in ZnPc-OPE-AuP⁺ recombines with a relatively low rate (k_BET = 1.0 × 10⁹ s^–1). In contrast, the rate for charge transfer in the other dyad, ZnPc-OPE-C₆₀, is relatively slow (k_PET = 1.1 × 10⁹ s^–1), while the recombination is very fast (k_BET ≈ 5 × 10¹⁰ s^–1). TD-DFT calculations support the hypothesis that the long-lived charge-shifted state of ZnPc-OPE-AuP⁺ is due to relaxation of the reduced gold porphyrin from a porphyrin ring based reduction to a gold centered reduction. This is in contrast to the faster recombination in the tin(IV) porphyrin based system (k_BET = 1.2 × 10¹⁰ s^–1), where the excess electron is instead delocalized over the porphyrin ring.