Triggering Reversible Optical Transformation of Monolayer WSe₂ via Photoswitchable and Cleavable Solid Azobenzene Material

Stimuli engineering physical properties of transition metal dichalcogenides (TMDCs) have attracted intense interest due to the intriguing potential in future optoelectronics, valleytronics, and quantum information science. Azobenzene molecules provide an ideal platform to manipulate the optical properties of monolayer TMDCs. Here, we employed reversibly photoswitchable and mechanically cleavable solid azobenzene derivative polycrystal to fabricate van der Waals heterostructure and elucidated the interface interaction between the azobenzene molecule and monolayer WSe₂ via visible laser-driven isomerization. The stronger coupling effect and dipole reorientation induced by the solid-liquid phase transition and the <i>trans</i>-to-<i>cis</i> conversion led to significant variation in electron doping to monolayer WSe₂. It is evidenced by the distinct photoluminescence (PL) quenching at room temperature and the pronounced shift from neutral exciton to negative trion through temperature- and gate-dependent PL and the variation of surface potentials of monolayer WSe₂ and the heterostructure. Our work thus provides a feasible approach to selectively and reversibly engineer 2D materials, which could lay a versatile path to the development of information processing, functional photoresponsive devices, and molecular probes.