Study on the Extent of Folding Back Conformation in Poly(aryl ether) Dendrimers by Intramolecular Electron Transfer and Exciplex Formation

• Published in: Macromolecules 2007-12, Vol.40 (26), p.9384-9390
• Main Authors: Li, Ying-Ying, Han, Lei, Chen, Jinping, Zheng, Shaojun, Zen, Yi, Li, Yi, Li, Shayu, Yang, Guoqiang
• Format: Article
• Language: English
• Subjects: Applied sciences; Exact sciences and technology; Organic polymers; Physicochemistry of polymers; Properties and characterization; Solution and gel properties
• ISSN: 0024-9297; 1520-5835
• DOI: 10.1021/ma071901w

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.