Probing the Intrachain and Interchain Effects on the Fluorescence Behavior of Pentiptycene-Derived Oligo(p-phenyleneethynylene)s
Resource
Journal of the American Chemical Society 128: 14109-14119
Journal
Journal of the American Chemical Society 128
Journal Volume
128
Journal Issue
43
Pages
14109-14119
Date Issued
2006
Date
2006
Author(s)
Yan, Jyu-Lun
Hwang, Chung-Yu
Chiou, Shih-Yi
Liau, Kang-Ling
Tsai, Hui-Hsu Gavin
Lee, Gene-Hsiang
Peng, Shie-Ming
Abstract
The synthesis, crystal structure, and fluorescence behavior of acetylene-bridged pentiptycene dimer (2), trimer (3), and tetramer (4) are reported. For comparison, a phenylene-pentiptycene-phenylene three-ring system (5) is also investigated. As a result of the unique intrachain pentiptycene-pentiptycene interactions in 3 and 4, their twisted conformers are populated in polar solvents and at low temperatures, and the phenomenon of nonequilibration of excited rotational conformers is observed. Twisting of the pi-conjugated backbones leads to blue-shifted absorption and fluorescence spectra and increased fluorescence quantum yields and lifetimes. The fluorescence spectra of 2-4 undergo small red shifts but large intensity variations in the 0-1 vs 0-0 bands on going from solutions to thin solid films, which can be accounted for by the reabsorption effect. However, the reduction in fluorescence quantum yields for 2-4 in films vs solutions is mainly attributed to efficient interchain exciton migration to nonfluorescent energy traps. In contrast, the behavior of nonequilibration of excited rotamers is not observed for 5 in solutions. Compound 5 forms J-type aggregates through terminal phenylene pi-stackings in the solid state, resulting in a new absorption band at 377 nm and large red shifts of the structured fluorescence spectra.
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journal article
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