Photoinduced excited-state hydrogen bonding strengthening of hemiindigo for the drastically fluorescence quenching in protic solvent and water sensing in aprotic solvent

Hydrogen bonding in excited state could regulate the photochemical and photophysical processes of organic molecules. In this work, the fluorescence and photoisomerization properties of Hemiindigo (HI) in dioxane and methanol have been studied. Its fluorescence is bright in dioxane but faint in methanol and the photoisomerization in methanol is distinctly inefficient when compared with that in dioxane. By using time-resolved spectroscopy technology and quantum chemical calculation, hydrogen bonding strengthening between solutes and solvents in excited state, which induces enormously enhanced efficiency of internal conversion of HI in excited state, is assigned to the reason of significant fluorescence quenching and inefficient photoisomerization of HI in methanol. Because of the drastically fluorescence quenching effect of HI, trace water sensing with a limit of detection of 10 ppm in dioxane suggests the potential of HI as a fluorescence probe to quantitate the water content in aprotic organic solvents. Hydrogen bonding in excited state could regulate the photochemical and photophysical processes of organic molecules. In this work, the fluorescence and photoisomerization properties of Hemiindigo (HI) in dioxane and methanol have been studied. Its fluorescence is bright in dioxane but faint in methanol and the photoisomerization in methanol is distinctly inefficient when compared with that in dioxane. By using time-resolved spectroscopy technology and quantum chemical calculation, hydrogen bonding strengthening between solutes and solvents in excited state, which induces enormously enhanced efficiency of internal conversion of HI in excited state, is assigned to the reason of significant fluorescence quenching and inefficient photoisomerization of HI in methanol. Because of the drastically fluorescence quenching effect of HI, trace water sensing with a limit of detection of 10 ppm in dioxane suggests the potential of HI as a fluorescence probe to quantitate the water content in aprotic organic solvents.