E/Z photoisomerization-induced photostability in benzylcyanocoumarin dyes and their coatings

In this study, benzylcyanocoumarin derivatives with various functional groups were designed and synthesized to maximize lightfastness. Notably, we propose an innovative strategy to enhance color stability by controlling the E/Z photoisomerization reaction. The optical properties of the synthesized dyes were evaluated, revealing that the E and Z isomers exhibit similar optical absorption spectra and maintain stable coloration performance despite photoisomerization. The observed color stability is attributed to the increased linearity upon conversion to the Z form, which maintains conjugation due to the push-pull effect between electron-donating and electron-withdrawing groups, resulting in absorption characteristics comparable to those of the E form structure. Additionally, lightfastness tests were conducted on PMMA-based spin-coated films containing the synthesized dyes under accelerated UV-A irradiation. The results demonstrated that the films exhibited minimal color change even under intense UV exposure, confirming their excellent lightfastness. This study provides evidence that molecular design strategies controlling E/Z photoisomerization can enhance the lightfastness of organic dyes and pigments. Moreover, despite not possessing a polycyclic structure, the synthesized dyes present a promising approach for designing highly photostable organic dyes and pigments. These findings are expected to contribute significantly to the development of functional organic coating materials, solar energy applications, and display technologies, where superior colorimetric stability is required.