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

An artificial light-harvesting multiporphyrin dendrimer (8P(Zn)P(FB)) composed of a focal freebase porphyrin (P-FB) with eight zinc(II) porphyrin (P-Zn) 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 8P(Zn)P(FB) and meso-tetrakis(4-pyridyl)-porphyrin (TPyP) for which the first and second association constants were estimated to be > 10(8) m(-1) and 3.0 x 10(7) m(-1), respectively. 8P(Zn)P(FB) originally shows 94% energy transfer efficiency from P-Zn to the focal P-FB. By the formation of the host-guest complex (8P(Zn)P(FB) 2TPyP) the emission intensity of 8P(Zn)P(FB) is significantly decreased, and an ultrafast charge separation state is generated. The energy transfer process from P-Zn wings to the P-FB core in 8P(Zn)P(FB) is almost entirely switched to an electron transfer process by the formation of 8P(Zn)P(FB)center dot 2TPyP.