Interaction of Water at the Hydrophobic Interface of Alkyl Group of Alcohol with p-Nitro-Aniline Charge Transfer State

摘要

The evolution of photo-induced intra molecular charge transfer (ICT) transition energy of p-nitro-aniline (PNA), with respect to the mole fraction of alcohol in alcohol water mixture has been used to study, the interaction of hydrophobic hydration -shell of linear alcohols with PNA-ICT state. The linear alcohol ranges from methanol to propanol. The plot of absorption energy of PNA charge transfer transition versus mole fraction of alcohol shows the following features. At lower mole fraction of alcohol, the absorption energy of PNA versus mole-fraction of alcohol plot at first, decreases below the absorption energy of PNA recorded in pure water and alcohol, goes through a minimum and then increases. Similar behaviour is obtained even after subtracting the contribution from dielectric non-ideality. The behaviour at lower mole fraction thus indicates the modifica- tion of specific interaction of PNA with water due to the presence of alcohol. Further, the absorption energy minimum shifts towards lower mole fraction of alcohol as the chain length of alcohol increases. These results, thus reveals the interaction of PNA with the modified water structure at the hydrophobic interface of alkyl group and supports the current understanding of hydrophobic hydration. To our knowledge, this study for the first time reveals that, hydration shell around hydrophobic group has higher ability to stabilize the PNA-ICT state by hydrogen bonding interaction compared to bulk water.