Azole‐Based Diarylbenzenes for Molecular Solar Thermal Energy Storage: A Computational Analysis

ABSTRACT Molecular solar thermal (MOST) energy storage systems rely on photoswitches that efficiently harvest, store, and release solar energy on demand. In this work, we present a comprehensive computational investigation of diarylbenzenes based on dithiazolyl (DTA) and dioxazolyl (DOA) cores to evaluate their suitability for MOST applications. Our calculations demonstrate that DOA switches bearing alkyl substituents at the lateral positions of the azole core simultaneously achieve large energy storage densities (0.29–0.39 MJ kg −1 ) and long energy storage times (11–55 days). Through intrinsic reaction coordinate (IRC) calculations, we illustrate that the photoinduced electrocyclization of the aromatic ring‐open form into the nonaromatic ring‐closed photoproduct of these switches proceeds in a barrierless manner. Interestingly, we find that the diradicaloid character of the symmetry‐forbidden TS mediating thermal cycloreversion of the photoproduct enables modulation of the TS energetics through conjugation by aryl substituents on the azole core, thereby lowering the cycloreversion barriers in aryl‐substituted DOA switches by up to 17 kJ mol −1 relative to the alkyl‐substituted ones. While such lowering is an undesirable feature for MOST applications, the diradicaloid nature of TS facilitates retrieval of the stored energy under the action of an acid catalyst, owing to the electron‐withdrawing nature of the protonated system that stabilizes the diradicaloid TS.