Natural photosynthetic light-harvesting systems have not only high efficient in energy transfer but also continuous conversion of light energy to other forms. Natural light-energy conversion is initiated by photon absorption of complex molecular assemblies called light-harvesting antenna complexes (LHC). Well-ordered three-dimensional multiporphyrin arrays in LHC facilitate effective photon capture and energy migration to the reaction center, which is composed of a non-covalently associated pair of chromophore units. Based on the process of natural photosynthetic systems, many chemists have reported highly efficient energy transfer. However, few studies have been conducted to control energy transfer pathway by guest binding.
In this study, triazole-bearing porphyrin triad (PZnTz-2PFB) consists of central zinc porphyrin (PZnTz) and two freebase porphyrin wings (PFB). PZnTz-2PFB exhibited unique photoluminescence switching phenomena by guest binding. As a result of fluorescence spectroscopy, PZnTz-2PFB exhibited the emission of freebase porphyrin regardless of excitation wavelength, and this result suggests that effective energy transfer takes place from PZn to PFB. After the addition of cyanide, emission spectrum of PZnTz-2PFB was consistent with the emission of CN- complex of PZn whether PFB or PZn excitation.