Aza-bicyclodiene based photoswitches for molecular solar thermal energy storage

Abstract

Harnessing and storage of solar radiations employing molecular photoswitches are certainly of intense research interest en route to alleviate the increasing energy demand. The present report aims to scrutinize the effect of N-Substitution on the photoswitching behaviour of bicyclodienes with different bridge lengths for molecular solar thermal energy storage (MOST) application. The result reveals that the bicyclodiene attains stability with an increase in bridge length due to a decreasing ring strain, while the photoproduct acquires strain and becomes destabilized. Consequently, as the bridge length increases, the storage energy is enhanced while the back reaction barrier decreases. The photoswitching properties can be greatly altered based on the position of N in aza-bicyclodiene. Aza-bicyclodiene photoswitches are isobaric with the parent systems and do not reduce the energy storage density, unlike the bulky electron releasing and withdrawing substituents. N-substitution at the bridgehead position enhances the thermal back reaction barrier without compromising the storage energy in long-bridged switches. Further, N-substitution is effective at shifting (bathochromic) the excitation wavelength to the longer wavelength region of the spectrum. Therefore, N-substitution in long-bridge bicyclodiene photoswitches could be beneficial to improve the thermochemical as well as photophysical properties for MOST application.