Theoretical Investigation On the Control of Macrocyclic Dihydroazulene/Azobenzene Photoswitches

In this work, we focus on macrocyclic structures comprised of two dihydroazulene (DHA) units and one azobenzene (AZB) unit and the possibility for photoisomerizing one unit selectively by tuning the excitation energies of each individual unit. An un- fortunate overlap between absorption bands of DHA and AZB as well as trans- and cis-AZB prevent us to have a full control on these macrocyclic structures and their ab- sorption need to be separated. By means of time-dependent density-functional theory (TD-DFT) calculations, we investigate the effects of ortho substitutions of the AZB unit by fluorine and chlorine atoms on the absorption spectra of the DHA/AZB macro- cycles. The calculations on the isolated AZB show that substitutions lead to distortion of the rings, due to the repulsive interactions between halogen atoms, and to a sys- tematic blue-shift of the ππ* bands between 25 nm to 50 nm. Moreover, separations between 10 nm to 48 nm, depending on the substituent, are observed in the nπ* bands. The resul...