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Updated: May 20, 2025

Time-Resolved Fluorescence Anisotropy from Single Molecules for Characterizing Local Flexibility in Biomolecules
Published on: April 25, 2025
Transient absorption and anisotropy studies of a push-pull azo derivative with an isomerization path-selective local
Rafael de Q Garcia1, Tiago Buckup2, Éléna Ishow3
1Instituto de Física de São Carlos, Universidade de São Paulo, Avenida Trabalhador São-Carlense, 400, CP 369, 13560970 São Carlos, SP, Brazil.
Abstract:
The ultrafast excited-state dynamics of the E and Z isomers of a push-pull nitroazobenzene containing an octupolar bis(4'-tert-butylbiphenyl-4-yl)aminophenyl electron donor group were studied with transient absorption (TA) and TA anisotropy. A comprehensive study with two excitation wavelengths and a broadband white-light continuum probe (400-1400 nm) has determined that a torsional isomerization mechanism is the most probable for both isomers. This has shed light on the excited state behavior of the elusive push-pull Z isomer, which has its properties mostly predicted by simulations and systematically lacks experimental observations. Meanwhile, another unproductive relaxation pathway, associated with a symmetric bending motion, was found only for the E isomer. When relaxing through this pathway, the molecule encounters a potential barrier in the ground state, which requires significant structural reorganization before full relaxation. This local minimum can be more general than expected and may be behind unsolved issues in the literature of azobenzenes.
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