Breaking aggregation in a tetrathiafulvalene-fused zinc porphyrin by metal-ligand coordination to form a donor-acceptor hybrid for ultrafast charge separation and charge stabilization

A novel electron rich, tetrathiafulvalene fused zinc porphyrin, (TTF)₄PZn, has been newly synthesized and characterized using spectral and electrochemical methods. In spite of the presence of eight t-butyl groups, (TTF)₄PZn exhibited appreciable aggregation in solution. Scanning electron microscopic (SEM) imaging of the aggregates revealed their spherical particulate morphology. Attenuation of intermolecular aggregation was possible by metal-ligand coordination of a nitrogenous ligand. Further, using this strategy, a donor-acceptor hybrid was formed by coordinating imidazole functionalized fullerene as an electron acceptor. The occurrence of intrasupramolecular ultrafast photoinduced charge separation has been established using fluorescence and transient absorption spectroscopic techniques. The determined rate of charge separation, k_CS, and rate of charge recombination, k_CR were found to be 1.4 × 10¹¹ s^-1 and 2.5 × 10⁶ s^-1, respectively. The lower k_CR values indicate charge stabilization in the assembled donor-acceptor conjugate via an electron transfer-hole transfer mechanism.