An unprecedented double photoexcitation mechanism for photoswitching in conjugated-dienes to trigger physiological processes for photopharmacology

The optical control of physiological processes with high precision using photoswitches is an emerging strategy for non-invasive diagnosis and therapies, providing innovative solutions to complex biomedical challenges. Light-responsive cyclic conjugated-dienes (cCDs) have long been recognized for their 4π-photocyclization; however, photoswitching behaviour in medium-sized cCDs has recently been reported, representing a pioneering discovery in the field. Reinforced by previous experimental evidence corroborating the Woodward-Hoffmann rules, this report provides insight into the origin of the exotic dual photoexcitation mechanism devised to achieve thermo-reversible photoswitching in large cCDs with cyclodeca-1,3-diene as a prototype. The operation of this mechanism enables access to four distinct photoisomers during a single photoswitching cycle, introducing new dimensions to the functionality of cCDs. Energy profiles calculated using M06-2X align closely with those obtained from DLPNO-CCSD(T), indicating its reliability as a method for predicting these systems, offering a balance between accuracy and computational cost. Time-dependent DFT calculations reveal that the important excitation wavelength of cCDs is significantly red-shifted compared to their photoproducts. The interaction behaviour of these isomers with β-barrel proteins was also analysed using molecular dynamics simulations to rationalize their potential for photopharmacology. The outcomes of the simulations show that photoisomers engage in different interactions inside the cavity, prompting variable conformational changes in the protein. Thus, the versatile architecture of cCDs can expand the toolbox of photoswitch designs for photoresponsive pharmaceuticals with photoisomers serving as mediators for precise reversible optical regulation of biological systems.