Abstract
Photoresponsive molecular interfaces in two-dimensional (2D) semiconductors enable light-programmable control of electronic and optical properties. However, how molecular photoisomerization reshapes interfacial electronic structure remains unclear. Here we introduce an interfacial framework that elucidates how photoisomerization of surface-bound spiropyran (SP) modulates interfacial charge distribution via molecular-state-dependent electrostatic interactions, enabling reversible modulation of photoluminescence (PL) emission and electric conductivity. In SP-functionalized WSe2 monolayers, visible light triggers formation of the closed-ring SP state that promotes nonradiative pathways and enhances current flow, whereas UV light converts it to the open-ring merocyanine (MC) form, restoring PL and conductivity. Density functional theory calculations with Bader charge and work function analyses reveal net charge variation of similar to 0.04 e per supercell and an accompanying work-function increase of approximately 0.16 eV, which may be responsible for the observed changes in PL and conductivity. Control experiments with WS2-SP show negligible changes, confirming that light-induced modulation depends on intrinsic material properties and surface potential alignment. These findings define interfacial charge reorganization as the mechanism linking molecular photoisomerization to optoelectronic properties and provide design strategies for light-addressable 2D hybrid systems.