The molecular thin films of Rose Bengal （RB） embedded in polymethyl methacrylate matrix are fabricated by using the spin-coating technique. The macroscopic current-voltage （I-V） characterization of the film shows that the RB molecule has two conductance switching states with a high ON/OFF ratio in ambient conditions. The infrared spectra indicate that intermolecular hydrogen bonds can form in the RB thin films after their hydrolysis in air. With the first-principles calculations, we demonstrate that the hydrogen bonds will be destroyed in concomitance with the conformational change when the RB molecule switches to its high-conductance state after applying a voltage.
