Intra-supramolecular electron transfer of the light harvesting porphyrin-phthalocyanine complex in aqueous medium

Report of the construction of the supramolecular light harvesting composed of zinc(II) phthalocyanine tetrasulfonic acid (ZnPcS4), as electron donor, and meso-tetra(N-methyl-4-pyridyl) porphyrin toluene sulfonate (TMPP), as electron acceptor. The steady-state absorption and fluorescence spectra of TMPP in MeOH showed the formation of monomer form (lambda(abs)(max) = 426 nm and lambda(flu)(max) = 654 and 715 nm). In water, different spectral features were recorded, suggesting the formation of aggregated forms. The formation of aggregated form in water was confirmed by recording the remarkable decrease of the fluorescence intensities of the singlet excited TMPP with increasing the concentrations of TMPP. In cationic micelle CTAB, both the absorption and fluorescence spectra were significantly decreased with increasing the concentrations of CTAB with a break at critical micelle concentration (CMC) at 6.00 x 10(-5) M. In an anionic micelle (SDS), the CMC value was found to be 1.00 x 10(-4) M. Upon interacting with ZnPcS4 in water, the steady state absorption measurement showed clear evidence for the formation of light harvesting porphyrin-phthalocyanine supramolecular complex through pi-pi and ionic interactions. The emission intensity of the singlet TMPP was found to significantly decrease in the presence of ZnPcS4 suggesting the intra-supramolecular electron transfer process from the electron donating ZnPcS4 to the electron deficient TMPP. From the fluorescence lifetime measurements, the rate and quantum yield of electron transfer were found to be 7.67 x 10(8) s(-1 )and 0.81, respectively. The finding of the examined light-harvesting supramolecular complex ZnPcS4-TMPP shows the ability to absorb the light in a wide range of the solar spectrum (UV-vis-NIR), in addition to the efficient electron transfer process in an aqueous medium, rendering it as a simple model of the artificial photosynthetic reaction center.