Effects of Hydrogen Bonding on Internal Conversion of GFP-like Chromophores. I. The para-Amino Systems
Journal
Journal of Physical Chemistry B
Journal Volume
117
Journal Issue
9
Pages
2695-2704
Date Issued
2013
Author(s)
Huang, Guan-Jhih
Cheng, Chi-Wen
Hsu, Hung-Yu
Prabhakar, Ch.
Lee, Yuan-Pern
Diau, Eric Wei-Guang
Abstract
To understand the effects of solvent-solute hydrogen bonding (SSHB) on the excited-state dynamics of two GFP-like chromophores, p-ABDI and p-CFABDI, we have determined the quantum yields for fluorescence (Φf) and the isomerization Z → E (ΦZE) and the femtosecond fluorescence and transient infrared absorption in selected solvents. The behavior that ΦZE ≅ 0.50 in aprotic solvents, such as CH3CN, indicates that the E-Z photoisomerization adopts a one-bond-flip mechanism through the torsion of the exocyclic C=C bond (the τ torsion) to form a perpendicular species (τ ∼90) in the singlet excited state followed by internal conversion (IC) to the ground state and partition to form the E and Z isomers with equal probabilities. The observed ΦZE decreased from 0.50 to 0.15-0.28 when CH3CN was replaced with the protic solvents CH3OH and CF3CH2OH. In conjunction with the solvent-independent rapid (<1 ps) kinetics for the fluorescence decay and the solvent-dependent slow (7-20 ps) kinetics for the ground-state recovery, we conclude that the SSHB modifies the potential energy surface for the τ torsion in a way that the IC occurs also for the twisted intermediates with a τ-torsion angle smaller than 90, which favors the formation of the Z isomers. The possibility of IC induced by torsion of the exocyclic C-C bond (the φ torsion) is also considered but excluded. © 2013 American Chemical Society.
SDGs
Type
journal article