Electronic transport characteristics of (Z)-2-allylidene-4a,8a-dihydronaphthalen-1(2H)-one as a potential optical molecular switch: a DFT–NEGF study

In this work, the electronic transport characteristics of a photochromic molecular system are investigated using the combined density functional theory (DFT) and nonequilibrium Green’s function (NEGF) formalism. The studied molecule undergoes a reversible photoinduced isomerization between its two forms under ultraviolet or visible light irradiation. A comprehensive analysis is performed of the current–voltage (I–V) characteristics, the electronic transmission spectra T(E), the effect of different electrode materials (Au, Ag, and Pt) on charge transport, the ON/OFF current ratio, and the spatial distributions of the molecular projected self-consistent Hamiltonian (MPSH) orbitals for both isomeric forms. The microscopic origin of the switching behavior is elucidated in terms of structural variations, the energetic positions and spatial delocalization of the frontier molecular orbitals, and changes in the HOMO–LUMO energy gap. The results demonstrate that the transformation from the dark to the colored form induces a pronounced transition from a high-conductance ON state to a low-conductance OFF state. Moreover, substantial variations in the transport properties are observed depending on the metal–molecule contact configuration. These findings highlight the strong structure–transport relationship in diarylethene-based (photochromic) molecular systems and provide valuable guidelines for the design and optimization of next-generation optoelectronic molecular devices.