Photoinduced electrical switching by a diarylethene polymer

Photoinduced electrical switching was investigated using photochromic diarylethenes (DA), which exhibit reversible photo-isomerization reactions with alternative UV/Vis light irradiation. Photo electrical switching could be introduced into DA molecules by connecting with electron conjugative groups (EC). The oxidation potential of the solution containing DA-EC polymer in a closed form was significantly shifted to a lower value compared to that of an open-form, indicating the electron conjugation in the closed form. The photochromic film prepared from the copolymer of DA-EC become dark colored upon exposure to a UV light source and the new absorption band centered at 570-620 nm was observed from the colored film. A solid cell structured as Au/DA-EC polymer/ITO showed characteristic I-V response. Significant increase in the current was observed from I-V plot for the cell after the UV light irradiation. Exposure of the cell to a visible light resulted in significant decrease in current. The electrical property of the film could be reversibly switched in a solid cell by alternatively irradiating the cell with UV and Vis light. The current-voltage (I-V) characteristics of the cell was related to the photochromic reaction from the colored ring-closed form to the bleached ring-open form state. Thus DA-EC polymer structure is a viable model for a photochromic electrochemical switch, to produce a persistent reversible electrochemical switching vis photon mode.