Triplet Spin Delocalization and Temperature Dependence for Adiabatic and Non-Adiabatic Z–E Isomerization Pathways in Azoarenes
Year: 2025
Type: article
Abstract: Photoswitching molecules like the azoarenes have myriad potential applications, ranging from energy storage to targeted drug delivery. Upon irradiation, azoarenes convert from an E -form to a Z -form. The Z -form can thermally revert to the E -form through a classical-adiabatic or a triplet-assisted rotational mechanism. We show that strategic placements of heteroatoms and substituents can modulate spin delocalization in the triplet state, thereby tuning the S 0 –T 1 –S 0 crossing points. Increased spin delocalization lowers the crossing point and shortens the thermal half-life of the Z -form. Computed spin densities at the diazo N atoms, along with computed S 0 –T 1 –S 0 crossing points, activation entropies, and rate constants for 15 azoarenes are compared with available experimental data. There is evidence that some of the studied Z – E isomerizations proceed simultaneously via a classical-adiabatic and a triplet-assisted mechanism. The ratio of the two reaction pathways is temperature-dependent. Triplet spin density at the diazo N atoms is recognized as a useful indicator for predicting the thermal half-lives of these species.
DOI: 10.1021/jacs.5c09852
Authors: Francisco A. Martins, Renan V. Viesser, João Vitor Schober, Rainer Herges, Judy I. Wu
Language: English
Subfield: Materials Chemistry
Field: Materials Science
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W4414326407