Theoretical investigation on vibrational frequency fluctuations of SCN-derivatized vibrational probe molecule in water

In this study, we theoretically investigate microscopic mechanism of the SCN vibrational frequency fluctuations of 2-nitro-5-thiocyanate benzoic acid (NTBA) in H2O by classical molecular dynamics simulation. Based on the vibrational solvatochromic theory, the decay components in the frequency-frequency time correlation function (FFTCF) of NTBA in H2O are characterized with time constants of 0.13 ps and 1.43 ps. We find the hydration structure and water dynamics in the vicinity of the vibrational probe of NTBA are similar to those in bulk. We consider that the electrostatic interactions with bulk-like water molecules around NTBA induce the slow decay component (i.e. 1-ps decay component) of the FFTCF of NTBA in H2O. (C) 2018 Published by Elsevier B.V.