For conjugated macrocycles, conformational disorder plays a key role in determining whether the unique form of excitons that are fully delocalized over the cyclic framework (cyclic excitons) is formed by photoexcitation. We have investigated the ring size dependence of conformations and photophysical properties of macrocyclic thiophenes of varying ring sizes (C-5NTNV) by using single-molecule fluorescence spectroscopy. We measured modulation depth, M, values and fluorescence intensities. As the ring size increases, the correlation plots of the two parameters show bimodal distributions, revealing that larger macrocycles exhibit extremely congested linear structures. The size dependence of structural changes in macrocyclic thiophenes have been clearly confirmed by molecular dynamics simulation. The number of torsional defects from simulated structures, in conjunction with survival times from fluorescence intensity trajectories and photon coincidence measurements, demonstrated the existence of multiple acyclic chromophores in the larger macrocycles from the ground state due to complete deformation of circular structures.
Bibliographical noteFunding Information:
We thank Prof. Masahiko Iyoda at Tokyo Metropolitan University for providing us with a series of C-5 N T N V investigated in this study. D.K. acknowledges support from Global Research Laboratory (2013K1A1A2A02050183) through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT (Information and Communication Technologies) and Future Planning. J.Y. acknowledges support from the Yonsei University Wonju Campus Future-Leading Research Initiative of 2018 (2018-62-0026). E.S. acknowledges support from the National Research Foundation of Korea (NRF) grant funded by the Korea government (MEST) (2017R1A2B2003552).
Copyright © 2019 American Chemical Society.
All Science Journal Classification (ASJC) codes
- Materials Science(all)
- Physical and Theoretical Chemistry