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Cooperative Conformational Change and Excitation Migration of Biphenyl-PMO Amorphous Film, As Revealed by Femtosecond Time-Resolved Spectroscopy
journal contribution
posted on 2014-05-08, 00:00 authored by Yukihide Ishibashi, Tetsuro Katayama, Hisayuki Saito, Ken-ichi Yamanaka, Yasutomo Goto, Takao Tani, Tadashi Okada, Shinji Inagaki, Hiroshi MiyasakaExcited
state dynamics of biphenyl-bridged mesoporous organosilica (Bp-PMO)
film was investigated by femtosecond transient absorption and dichroism
measurements at various excitation intensities. Under the excitation
condition with low intensity (ca. 0.1 μJ/pulse), the relaxation
from the excited Franck–Condon state with skewed structure
of the two phenyl rings to the preplanar state occurred with a time
constant of 550 fs, followed by the excimer formation with two time
constants of 9.0 and 140 ps. Under higher excitation condition with
1.0 μJ/pulse, very rapid excimer formation within 500 fs was
observed. From the analysis of the transient absorption spectra, it
was revealed that the cooperative geometrical relaxation from skewed
to planar structures, in addition to the energy migration, led to
the rapid excimer formation under the high excitation condition. By
integrating these results with the fluorescence dynamics, the photoprimary
processes in Bp-PMO, such as energy migration, annihilation, and excimer
formation, were discussed.