This study presents a comprehensive investigation into the structural and electronic transport characteristics of the E and Z isomers of 2-((1H-pyrrol-2-yl)methylene)indolin-3-one, a representative hemi-indigo molecular switch, employing density functional theory (DFT) combined with nonequilibrium Green’s function (NEGF) formalism. These bistable molecules exhibit reversible isomerization under visible or ultraviolet (UV) light, making them attractive candidates for optoelectronic applications. The spectroscopic properties, including infrared (IR), nuclear magnetic resonance (NMR), and UV spectra, were analyzed using the hybrid B3LYP/6-311++Gd,p) level of theory. Detailed analysis reveals significant differences in bond lengths, bond angles, highest occupied molecular orbital (HOMO)–lowest unoccupied molecular orbital (LUMO) gaps, and current–voltage (I–V) responses between the two isomers. The E isomer consistently demonstrates superior electronic conductivity, with enhanced switching behavior most notably observed in configurations involving Ag electrodes and hollow binding sites. Transmission spectra T(E), second-order interaction energies (E2), and molecular projected self-consistent Hamiltonian (MPSH) orbital maps further elucidate charge transport pathways and isomer-dependent conduction features. Additionally, the effect of chemical functionalization on device performance was systematically explored by substituting hydrogen atoms with electron-donating (–NH2) and electron-withdrawing (–CN) groups at three strategic molecular positions (X, Y, Z). Notably, –CN substitution at the Y position significantly improved the current on/off ratio at operating voltages below 1.4 V, demonstrating tunability of switching characteristics via targeted molecular modification. These findings underscore the potential of functionalized hemi-indigo derivatives as robust and efficient molecular switches for integration into next-generation nanoelectronics devices.

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