Construction of Segregated Arrays of Multiple Donor

Abstract: Dendritic molecules appended with multiple zinc porphyrin units (DPm,m [number of zinc porphyrin units] ) 6, 12, and 24) trap bipyridine compounds carrying multiple fullerene units (Py2Fn, n [number of C60 units] ) 1-3), affording coordination complexes DPm_Py2Fn having a photoactive layer consisting of spatially segregated donor and acceptor arrays on their surface. Complexes DPm_Py2Fn are stable enough (K [average binding affinity]) 1.1 _ 106-4.4 _ 106 M-1 in CHCl3 at 25 C) to be isolated by gel permeation chromatography. UHV-STM microscopy enables clear visualization of a petal-like structure of DP12_Py2F3. Photoexcitation of the zinc porphyrin units in DPm_Py2Fn results in a zinc porphyrin-to-fullerene electron transfer to generate a charge separation. The charge-separation rate constant (kCS) in CH2Cl2 at 20 C increases from 0.26 _ 1010 to 2.3 _ 1010 s-1 upon increment ofm and n, whereas the charge-recombination rate constant (kCR) remains almost unchanged at 4.5 _ 106-6.7 _ 106 s-1. Consequently, DP24_Py2F3 furnishes the largest ratio of kCS/kCR (3400) among the family.