Phys. Rev. B 60, 15632 - 15635 (1999)
[Issue 23 – December 1999]
Femtosecond relaxation kinetics of fluorescent and nonfluorescent states in blue- and red-phase polydiacetylenes

M. Yoshizawa, A. Kubo, and S. Saikan
Department of Physics, Graduate School of Science, Tohoku University, Aramaki-aza-aoba, Aoba-ku, Sendai 980-8578, Japan
Received 12 April 1999; revised 30 July 1999

Relaxation kinetics of photoexcitations in polydiacetylenes (PDA’s) has been investigated using femtosecond fluorescence spectroscopy. Transient response of the fluorescence in red-phase PDA has decay time constants of 160±40 fs, 0.8±0.1 ps, and 6.7±0.4 ps. The decay kinetics is consistent with transient absorbance changes observed by femtosecond photoinduced absorption spectroscopy. On the other hand, the fluorescence in blue-phase PDA disappears much faster than the transient absorbance change. The photoexcitations in red-phase PDA are fluorescent during the whole relaxation kinetics, but the photoexcited exciton in blue-phase PDA relaxes to nonfluorescent state within 170 fs.