Photoswitchable Imines: Aryliminopyrazoles Quantitatively Convert to Long-Lived Z-Isomers with Visible Light

Abstract

Arylimines offer promise in dynamic-covalent materials due to their recyclability and ease of synthesis. However, their light-triggered E/Z isomerism has received little attention. This is attributed to challenges that include low thermal stability of their metastable state (<60 s at 20 °C), incomplete photoswitching (<50% to the metastable state), and the need for UV light (≤365 nm). We overcome these limitations with a novel class of imine photoswitch, the aryliminopyrazoles (AIPs). These AIPs can be switched using visible light (470 nm), attain photostationary states with over 95% of the Z-isomer, exhibit great resistance to fatigue, and have thermal half-lives up to 19.2 hours at room temperature. Additionally, they display T-type and negative photochromism under visible light irradiation—a useful property. The quantitative assembly, accessibility of precursors, and recyclability set these photoswitches apart from their azo-based analogues. These findings open avenues for next-generation photoresponsive dynamic-covalent materials driven solely by these new photochromic linkages and further exploration of photocontrolled dynamic combinatorial chemistry.

Kinetic Trapping of an Out‐of‐Equilibrium Dynamic Library of Imines by Changing Solvent

“…These findings can contribute to a deeper understanding of the factors governing time-controlled transimination equilibria. [22]…”