Abstract:7-hydroxyquinoline (7-HQ) is a kind of organic molecule with excited state proton transfer (ESPT) effect, and can be used as the material for all optical switching. This optical switching takes place via the ESPT effect depending on its intermolecular hydrogen bond formed with the solvent, and can have the effect of all optical switching. 7-HQ can not form intermolecular hydrogen bond with dimethyl sulfoxide (DMSO), so 7-HQ in DMSO solution cannot display the ESPT effect. However, after the solution was radiated by an UV laser, we found that 7-HQ could have ESPT effect. This phenomenon is reported and the mechanism is investigated for the first time in this paper. Supported by National Natural Science Foundation of China (No. 60178025) and the Foundation of Optoelectronic Information and Technology Laboratory, EMC.