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

An artificial light-harvesting multiporphyrin dendrimer ( 8P_ZnP_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_ZnP_FB 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. 8P_ZnP_FB originally shows 94 % energy transfer efficiency from P_Zn to the focal P_FB. By the formation of the host-guest complex ( 8P_ZnP_FB⋅2 TPyP) the emission intensity of 8P_ZnP_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_ZnP_FB is almost entirely switched to an electron transfer process by the formation of 8P_ZnP_FB⋅2 TPyP. [ABSTRACT FROM AUTHOR]