Energy-transfer studies on phthalocyanine-BODIPY light harvesting pentad by laser flash photolysis

A molecular pentad, comprised of zinc phthalocyanine (ZnPc) with four boron dipyrromethene units (BODIPY) have been examined by femtosecond and nanosecond laser flash photolysis to explore its photoinduced intramolecular events from the excited BODIPY. The geometry optimization showed that the phthalocyanine moiety is completely symmetric and form perfect square planar complex with zinc. The absorption spectrum of ZnPc-BODIPY pentad covers most of the visible region (ca. 300-750 nm), which clearly is an advantage for capturing solar energy. The excitation transfer from the singlet BODIPY to ZnPc is envisioned due to good spectral overlap of the BODIPY emission and ZnPc absorption spectra. Femtosecond laser flash photolysis studies provided concrete evidence for the occurrence of energy transfer from the singlet excited BODIPY to ZnPc in tetrahydrofuran. The kinetic study of energy transfer measured by monitoring the decay of the BODIPY emission revealed fast energy transfer (5.90 x 10(10) s(-1)) in the molecular pentad. Since the electron transfer from the singlet ZnPc to BODIPY is thermodynamically not feasible, the singlet ZnPc decayed to populates the triplet ZnPc, in addition to the grounds state. These findings suggest the potential of the examined ZnPc-BODIPY pentad to be efficient photosynthetic antenna in the artificial photosynthetic systems.