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 π-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 π-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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Yang, J. (Contributor), Liau, K. (Contributor), Tsai, H. (Contributor), Yan, J. (Contributor), Lee, G. (Contributor), Hwang, C. (Contributor), Peng, S. (Contributor) & Chiou, S. (Contributor), The Cambridge Structural Database, 1 Jan 2007
Yang, J. (Contributor), Hwang, C. (Contributor), Lee, G. (Contributor), Chiou, S. (Contributor), Liau, K. (Contributor), Tsai, H. (Contributor), Yan, J. (Contributor) & Peng, S. (Contributor), The Cambridge Structural Database, 1 Jan 2007