π-Bridge Substitution in DASAs: The Subtle Equilibrium between Photochemical Improvements and Thermal Control** |
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Authors: | Dr David Martínez-López Eduardo Santamaría-Aranda Dr Marco Marazzi Dr Cristina García-Iriepa Dr Diego Sampedro |
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Institution: | 1. Departamento de Química, Centro de Investigación en Síntesis, Química (CISQ), University of La Rioja, Madre de Dios 53, 26006 Logroño, Spain;2. Department of Analytical Chemistry, Physical Chemistry and Chemical, Engineering, Universidad de Alcalá, Ctra. Madrid-Barcelona, km 33,600, 28871 Alcalá de Henares, Madrid, Spain |
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Abstract: | Donor–acceptor Stenhouse adducts (DASAs) are playing an outstanding role as innovative and versatile photoswitches. Until now, all the efforts have been spent on modifying the donor and acceptor moieties to modulate the absorption energy and improve the cyclization and reversion kinetics. However, there is a strong dependence on specific structural modifications and a lack of predictive behavior, mostly owing to the complex photoswitching mechanism. Here, by means of a combined experimental and theoretical study, the effect of chemical modification of the π-bridge linking the donor and acceptor moieties is systematically explored, revealing the significant impact on the absorption, photocyclization, and relative stability of the open form. In particular, a position along the π-bridge is found to be the most suited to redshift the absorption while preserving the cyclization. However, thermal back-reaction to the initial isomer is blocked. These effects are explained in terms of an increased acceptor capability offered by the π-bridge substituent that can be modulated. This strategy opens the path toward derivatives with infra-red absorption and a potential anchoring point for further functionalization. |
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Keywords: | DASA photochemistry photoswitches thermal equilibrium |
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