title: Relaxation dynamics of 2,7- and 3,6-distyrylcarbazoles in solutions and in solid films: mechanism for efficient nonradiative deactivation in the 3,6-linked carbazole.
abstract: We performed time-resolved spectral investigations of two distyrylcarbazole derivatives, 2,7- and 3,6-distyrylcarbazole (2,7-DPVTCz and 3,6-DPVTCz, respectively), in dilute toluene solution and in solid films mixed with poly(methyl methacrylate) (PMMA). The lifetime of 2,7-DPVTCz in its excited state in solution is approximately 100 times as great as that of 3,6-DPVTCz, consistent with their photophysical nature. The former shows intense emission, but the latter is nearly nonfluorescent in a free environment. Moreover, the lifetime of 3,6-DPVTCz in its excited state increased also approximately 100 times when the molecule was encapsulated in a 3,6-DPVTCz/PMMA solid film, indicating that intramolecular motion of the molecule significantly affects the observed relaxation dynamics in a confined environment. Calculations on the excited states indicate that an efficient intersystem crossing is activated upon twisting of the bridged C-C single bond in a free 3,6-linked carbazole; such efficient deactivation is impractical in 2,7-linked carbazole or for 3,6-linked carbazole in a PMMA matrix. Information obtained from experiments on femtosecond fluorescence enables us to distinguish crucial relaxation processes in the excited state for a profound understanding of the details of vibrational and electronic relaxations of 3,6-DPVTCz in solution.
authors.affiliation: Department of Applied Chemistry, Institute of Molecular Science, Center for Interdisciplinary Molecular Science, National Chiao Tung University, Hsinchu 30010, Taiwan.
authors.forename: Tsai-Te
authors.initials: TT
authors.lastname: Wang
authors.forename: Szu-Min
authors.initials: SM
authors.lastname: Chung
authors.forename: Fang-Iy
authors.initials: FI
authors.lastname: Wu
authors.forename: Ching-Fong
authors.initials: CF
authors.lastname: Shu
authors.forename: Eric Wei-Guang
authors.initials: EW
authors.lastname: Diau