Solvent-Modulated Charge-Transfer Resonance Enhancement in the Excimer State of a Bay-Substituted Perylene Bisimide Cyclophane

J Phys Chem Lett. 2019 Apr 18;10(8):1919-1927. doi: 10.1021/acs.jpclett.9b00357. Epub 2019 Apr 5.

Abstract

Excimer, a configurational mixing between Frenkel exciton and charge-transfer resonance states, is typically regarded as a trap state that hinders desired energy or charge-transfer processes in artificial molecular assemblies. However, in recent days, the excimer has received much attention as a functional intermediate in the excited-state dynamics such as singlet fission or charge-separation processes. In this work, we show that the relative contribution to charge-transfer resonance of the excimer state in a bay-substituted perylene bisimide dimer cyclophane can be modulated by dielectric properties of the solvents employed. Solvent-dependent time-resolved fluorescence and absorption measurements reveal that an enhancement of charge-transfer resonance in the excimer state is reflected by incomplete symmetry-breaking charge-separation processes from the structurally relaxed excimer state by means of dipolar solvation processes in the high dielectric environment.