Regulating and controlling the stepwise ESDPT channel of BP(OH)2DCEt2 using the strategy of solvent polarity and external electric field

Abstract

Excited state double proton transfer (ESDPT) has attracted great scientific interest because of its excellent luminescent properties. However, the complex process of ESDPT has plagued theoretical and experimental scientists for a long time and has become a hot issue. In this work, the ESDPT process of 2,2′-bipyridine-3,3′-diol-5,5′-dicarboxylic acid ethyl ester (BP(OH)₂DCEt₂) is systematically studied and the regulation of the ESDPT process is further realized. The potential energy curves indicate that BP(OH)₂DCEt₂ shows the characteristics of stepwise ESDPT in different polar solvents. The increase in solvent polarity will be beneficial to the stepwise ESDPT reaction. Regrettably, it is not possible to distinguish the specific stepwise transfer path of the BP(OH)₂DCEt₂ molecule due to the symmetry of the potential energy surface along the diagonal. On this basis, we proposed a method to control and regulate the stepwise ESDPT path using an external electric field. The results show that the increase of external electric field intensity is favorable to stepwise ESDPT. It is interesting to note that applying an external electric field in a specific direction will effectively distinguish stepwise ESDPT reaction paths. Therefore, this work not only helps to understand the mechanism of ESDPT, but also contributes to regulation and design of new luminescent materials with excellent luminescent properties.