Excited-State Dynamic Planarization of Cyclic Oligothiophenes in the Vicinity of a Ring-to-Linear Excitonic Behavioral Turning Point.
Excited-state dynamic planarization processes play a crucial role in determining exciton size in cyclic systems, as reported for π-conjugated linear oligomers. Herein, we report time-resolved fluorescence spectra and molecular dynamics simulations of π-conjugated cyclic oligothiophenes in which the number of subunits was chosen to show the size-dependent dynamic planarization in the vicinity of a ring-to-linear behavioral turning point. Analyses on the evolution of the total fluorescence intensity and the ratio between 0-1 to 0-0 vibronic bands suggest that excitons formed in a cyclic oligothiophene composed of six subunits fully delocalize over the cyclic carbon backbone, whereas those formed in larger systems fail to achieve complete delocalization. With the aid of molecular dynamics simulations, it is shown that distorted structures unfavorable for efficient exciton delocalization are more easily populated as the size of the cyclic system increases.
Department of Chemistry and Spectroscopy Laboratory for Functional π-Electronic Systems, Yonsei University, Seoul 120-749 (Korea).
Kyu Hyung
KH
Park
Department of Chemistry and Spectroscopy Laboratory for Functional π-Electronic Systems, Yonsei University, Seoul 120-749 (Korea).
Pyosang
P
Kim
Department of Chemistry and Spectroscopy Laboratory for Functional π-Electronic Systems, Yonsei University, Seoul 120-749 (Korea).
Woojae
W
Kim
Department of Chemistry, Graduate School of Science and Engineering, Tokyo Metropolitan University, Tokyo 192-0397 (Japan).
Hideyuki
H
Shimizu
Department of Chemistry and Institute of Nano-Bio Molecular Assemblies, Yonsei University, Seoul 120-749 (Korea).
Minwoo
M
Han
Department of Chemistry and Institute of Nano-Bio Molecular Assemblies, Yonsei University, Seoul 120-749 (Korea). esim@yonsei.ac.kr.
Eunji
E
Sim
Department of Chemistry, Graduate School of Science and Engineering, Tokyo Metropolitan University, Tokyo 192-0397 (Japan). iyoda@tmu.ac.jp.
Masahiko
M
Iyoda
Department of Chemistry and Spectroscopy Laboratory for Functional π-Electronic Systems, Yonsei University, Seoul 120-749 (Korea). dongho@yonsei.ac.kr.
Dongho
D
Kim
conformation analysis; conjugation; excitons; oligothiophenes; photophysics