914487-85-7Relevant academic research and scientific papers
Mechanisms, pathways, and dynamics of excited-state energy flow in self-assembled wheel-and-spoke light-harvesting architectures
Song, Hee-Eun,Kirmaier, Christine,Schwartz, Jennifer K.,Hindin, Eve,Yu, Lianhe,Bocian, David F.,Lindsey, Jonathan S.,Holten, Dewey
, p. 19121 - 19130 (2006)
Static and time-resolved optical measurements are reported for two cyclic hexameric porphyrin arrays and their self-assembled complexes with guest chromophores. The hexameric hosts contain zinc porphyrins and 0 or 3 free base (Fb) porphyrins (denoted Zn6 or Zn3Fb3, respectively). The guests are a tripyridyl arene (TP) and a dipyridyl- substituted free base porphyrin (DPFb), each of which coordinates to zinc porphyrins of a host via pyridyl-zinc dative bonding. Each architecture is designed to have an overall gradient of excitedstate energies that affords excitation funneling within the host and ultimately to the guest. Collectively, the studies delineate the various pathways, mechanisms, and rate constants of energy flow among the weakly coupled constituents of the host-guest complexes. The pathways include downhill unidirectional energy transfer between adjacent chromophores, bidirectional energy migration between identical chromophores, and energy transfer between nonadjacent chromophores. The energy transfer to the lowest-energy chromophore(s) within the backbone of a hexameric host (Fb porphyrins in Zn3Fb3 or pyridyl-coordinated zinc porphyrins in Zn6·TP and Zn6·DPFb) proceeds primarily via a through-bond mechanism; the transfer is rapid (～40 ps depending on the array) and essentially quantitative (≥98%). The energy transfer from a pyridyl-coordinated zinc porphyrin of the host to the Fb porphyrin guest in the Zn6·DPFb complex is almost exclusively Foerster through-space in nature; this process is much slower (～1 ns) and has a lower yield (65%). These studies highlight the utility of cyclic architectures for efficient light harvesting and energy transfer to a designated trapping site.
