Theoretical analysis of an all-photonic multifunctional molecular logic device: Using TD-DFT//DFT to assess photochromic activity of multimeric photochrome

The structures and properties of a single-molecule photochromic switch consisting of 3 photochromic moieties is investigated. Using time-dependent density functional theory (TD-DFT) we calculated the λmax within ± 30 nm (± 0.18 eV) and produced spectra that were similar. The charge-transfer (CT) character of the molecular orbitals (MO) was assessed via the overlap between the occupied and virtual orbitals (Λ diagnostic) and did not suffer from CT failure. The MOs were consistent with photochemically productive photochromes. The MO and their contribution to different excited states paralleled both the observed activity and observed inactivity of the photochrome.