title: Probing the intrachain and interchain effects on the fluorescence behavior of pentiptycene-derived oligo(p-phenyleneethynylene)s.
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.
authors.affiliation: Department of Chemistry, National Taiwan University, Taipei, Taiwan 10617. jsyang@ntu.edu.tw
authors.forename: Jye-Shane
authors.initials: JS
authors.lastname: Yang
authors.forename: Jyu-Lun
authors.initials: JL
authors.lastname: Yan
authors.forename: Chung-Yu
authors.initials: CY
authors.lastname: Hwang
authors.forename: Shih-Yi
authors.initials: SY
authors.lastname: Chiou
authors.forename: Kang-Ling
authors.initials: KL
authors.lastname: Liau
authors.forename: Hui-Hsu
authors.initials: HH
authors.lastname: Gavin Tsai
authors.forename: Gene-Hsiang
authors.initials: GH
authors.lastname: Lee
authors.forename: Shie-Ming
authors.initials: SM
authors.lastname: Peng