Synthesis and Photodynamics of Fluorescent Blue BODIPY-Porphyrin Tweezers Linked by Triazole Rings

Novel zinc porphyrin tweezers in which two zinc porphyrins were connected with pi-conjugated boron dipyrromethenes (BDP meso-Por(2) and BDP beta-Por(2)) through triazole rings were synthesized to investigate the photoinduced energy transfer and electron transfer. The UV-vis spectrum of BDP beta-Por(2) which has less bulky substituents than BDP meso-Por(2) exhibits splitting of the Soret band as a result of the interaction between porphyrins of BDP beta-Por(2) in the excited state. Such interaction between porphyrins of both BDP beta-Por(2) and BDP meso-Por(2) is dominant at room temperature, while the coordination of the nitrogen atoms of the triazole rings to the zinc ions of the porphyrins occurs at low temperature. The conformational change of the BDP-porphyrin composites was confirmed by the changes in UV-vis and fluorescence spectra depending on temperature. Photodynamics of BDP meso-Por2 and BDP beta-Por(2) has also been investigated by laser flash photolysis. Efficient singlet-singlet energy transfer from the ZnP to the pi-conjugated BDP moiety of both BDP meso-Por2 and BDP beta-Por(2) occurred in opposite direction as compared to energy transfer from conventional BDP to ZnP due to the pi-conjugation in nonpolar toluene. In polar benzonitrile, however, additional electron transfer occurred along with energy transfer.