Theoretical Insights into Excited-State Intermolecular Proton Transfers of 2,7-Diazaindole in Water Using a Microsolvation Approach

The detailed excited-state intermolecular proton transfer (ESInterPT) mechanism of 2,7-diazaindole with water wires consisting of either one or two shells [2,7-DAI(H2O)(n); n = 1 -5] has been theoretically explored by time-dependent density functional theory using microsolvation with an implicit solvent model. On the basis of the excited-state potential energy surfaces along the proton transfer (PT) coordinates, among all 2,7-DAI(H2O)(n,) the multiple ESInterPT of 2,7-DAI(H2O)(2+3) through the first hydration shell (inner circuit) is the most easy process to occur with the lowest PT barrier and a highly exothermic reaction. The lowest PT barrier resulted from the outer three waters pushing the inner circuit waters to be much closer to 2,7-DAI, leading to the enhanced intermolecular hydrogen-bonding strength of the inner two waters. Moreover, on-thefly dynamic simulations show that the multiple ESInterPT mechanism of 2,7-DAI(H2O)(2+3) is the triple PT in a stepwise mechanism with the highest PT probability. This solvation effect using microsolvation and dynamic simulation is a cost-effect approach to reveal the solvent-assisted multiple proton relay of chromophores based on excited-state proton transfer.

Automated summary

This study theoretically explored the excited-state intermolecular proton transfer mechanism of 2,7-diazaindole with water wires containing one or two shells. It found that the multiple proton transfer through the first hydration shell is the easiest process to occur with the lowest barrier and a highly exothermic reaction.