First principle evaluation of the chiroptical activity of the di-phenyl-diazene derivatives

Azobenzene (di-phenyl-diazene) is well-known as a photoisomerisable molecule and has been widely studied as a molecular photoswitcher. Molecular rods, where di-phenyl arms are bound to the diazene moiety, have been also synthesized. In this article we explore by first principle density functional theory calculations the chiroptical properties (electronic circular dichroism spectra, ECD) of azobenzene and its homologues with polyphenyl arms. In particular, we demonstrate that for molecules in the cis configuration the intrinsic chirality of the distorted cis diazene group dominates the ECD response, while for trans species the non-planarity of the polyphenyl arms induces peaks in the ECD spectrum. Finally, the possibility of obtaining a light-controlled chiral switch by proper functionalization is also speculated.