title: Construction of segregated arrays of multiple donor and acceptor units using a dendritic scaffold: remarkable dendrimer effects on photoinduced charge separation.
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 superset Py2Fn having a photoactive layer consisting of spatially segregated donor and acceptor arrays on their surface. Complexes DPm superset Py2Fn are stable enough (K [average binding affinity] = 1.1 x 10(6)-4.4 x 10(6) M(-1) in CHCl3 at 25 degrees C) to be isolated by gel permeation chromatography. UHV-STM microscopy enables clear visualization of a petal-like structure of DP12 superset Py2F3. Photoexcitation of the zinc porphyrin units in DPm superset 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 degrees C increases from 0.26 x 10(10) to 2.3 x 10(10) s(-1) upon increment of m and n, whereas the charge-recombination rate constant (kCR) remains almost unchanged at 4.5 x 10(6)-6.7 x 10(6) s(-1). Consequently, DP24 supersetPy2F3 furnishes the largest ratio of kCS/kCR (3400) among the family.
authors.affiliation: ERATO-SORST Nanospace Project, Japan Science and Technology Agency (JST), National Museum of Emerging Science and Innovation, 2-41 Aomi, Koto-ku, Tokyo 135-0064, Japan. li@nanospace.miraikan.jst.go.jp
authors.forename: Wei-Shi
authors.initials: WS
authors.lastname: Li
authors.forename: Kil Suk
authors.initials: KS
authors.lastname: Kim
authors.forename: Dong-Lin
authors.initials: DL
authors.lastname: Jiang
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Tanaka
authors.forename: Tomoji
authors.initials: T
authors.lastname: Kawai
authors.forename: Jung Ho
authors.initials: JH
authors.lastname: Kwon
authors.forename: Dongho
authors.initials: D
authors.lastname: Kim
authors.forename: Takuzo
authors.initials: T
authors.lastname: Aida
mesh_terms: D050091:Dendrimers / Q000737:chemistry*; D016252:Microscopy, Scanning Tunneling; D008954:Models, Biological; D009942:Organometallic Compounds / Q000737:chemistry*; D010777:Photochemistry; D011166:Porphyrins / Q000737:chemistry*; D013499:Surface Properties; D015032:Zinc / Q000737:chemistry*
chemical_list: D050091:Dendrimers; D009942:Organometallic Compounds; D011166:Porphyrins; D015032:Zinc