Web Release Date: December 4,
Study on the Extent of Folding Back Conformation in Poly(aryl ether) Dendrimers by Intramolecular Electron Transfer and Exciplex Formation
and
Laboratory of Organic Optoelectronic Functional Materials and Molecular Engineering, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100080, P. R. China, and Graduate School, Chinese Academy of Sciences, Beijing 100039, P. R. China
and
Beijing National Laboratory for Molecular Sciences (BNLMS), Key Laboratory of Photochemistry, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100080, P. R. China
Received August 22, 2007
Revised Manuscript Received October 23, 2007
Abstract:
A series of poly(aryl ether) dendrimers (Py-Gn-NHPh, n = 1-4) with only one pyrene chromophore at the periphery and an aniline group at the core were synthesized and the extent of folding back conformation was given by the intramolecular electron transfer and exciplex formation. Selective excitation of the periphery pyrene moiety of Py-Gn-NHPh in dichloromethane resulted in an electron-transfer process from aniline to pyrene, and as a consequence of the electron transfer, an intramolecular exciplex was formed. Since the exciplex formation requires a direct orbital overlap between the donor and the acceptor groups, this gives us a direct experimental observation for the folding back conformation of poly(aryl ether) dendrimers. The efficiencies and the rate constants of electron transfer in dichloromethane are measured to be 0.90, 0.83, 0.78, 0.68, and 3.6 × 108, 1.7 × 108, 1.2 × 108, and 6.6 × 107 s-1 for generations 1-4, respectively. The separations (center to center) between the core donor group and the periphery acceptor chromophore are estimated from the rate constants of electron transfer, which are 7.7, 8.0, 8.2, and 8.5 Å for generations 1-4, respectively. This means that the periphery chromophores can fold inward and reach to the core vicinity for all four generations.
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