Guest-Induced Photophysical Property Switching of Artificial Light-Harvesting Dendrimers

An artificial light‐harvesting multiporphyrin dendrimer (8PZnPFB) composed of a focal freebase porphyrin (PFB) with eight zinc(II) porphyrin (PZn) wings exhibited unique photophysical property switching in response to specific guest molecule binding. UV/Vis titration studies indicated stable 1:2 host–guest complex formation between 8PZnPFB and meso‐tetrakis(4‐pyridyl)‐porphyrin (TPyP) for which the first and second association constants were estimated to be >108 M−1 and 3.0×107 M−1, respectively. 8PZnPFB originally shows 94 % energy transfer efficiency from PZn to the focal PFB. By the formation of the host–guest complex (8PZnPFB⋅2TPyP) the emission intensity of 8PZnPFB is significantly decreased, and an ultrafast charge separation state is generated. The energy transfer process from PZn wings to the PFB core in 8PZnPFB is almost entirely switched to an electron transfer process by the formation of 8PZnPFB⋅2TPyP. Multiporphyrin dendrimers exhibit an excellent excitation energy transfer from the zinc porphyrin wings to the focal free‐base porphyrin. The energy transfer is switched to an ultrafast electron transfer by the formation of a host–guest complex with tetrapyridyl porphyrin guests (green in picture). Thus, the multiporphyrin dendrimers serve as unique biomimetic models for both light‐harvesting complexes LHC1 and LHC2.