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Guest-Induced Modulation of the Energy Transfer Process in Porphyrin-Based Artificial Light Harvesting Dendrimers

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journal contribution
posted on 2016-12-15, 00:00 authored by Dajeong Yim, Jooyoung Sung, Serom Kim, Juwon Oh, Hongsik Yoon, Young Mo Sung, Dongho Kim, Woo-Dong Jang
A series of dendritic multiporphyrin arrays (PZnTz-nPFB; n = 2, 4, 8) comprising a triazole-bearing focal zinc porphyrin (PZn) with a different number of freebase porphyrin (PFB) wings has been synthesized, and their photoinduced energy transfer process has been evaluated. UV/vis absorption, emission, and time-resolved fluorescence measurements indicated that efficient excitation energy transfer takes place from the focal PZn to PFB wings in PZnTz-nPFB’s. The triazole-bearing PZn effectively formed host–guest complexes with anionic species by means of axial coordination with the aid of multiple C–H hydrogen bonds. By addition of various anionic guests to PZnTz and PZnTz-nPFB’s, strong bathochromic shifts of PZn absorption were observed, indicating the HOMO–LUMO gap (ΔEHOMO–LUMO) of PZn decreased by anion binding. Time-resolved fluorescence measurements revealed that the fluorescence emission predominantly takes place from PZn in PZnTz-nPFB’s after the addition of CN. This change was reversible because a treatment with a silver strip to remove CN fully recovered the original energy transfer process from the focal PZn to PFB wings.