Unveiling the Role of Water on π–π Stacking Through Microwave Spectroscopy of (Thiophene)₂-(Water)_1–2 Clusters

Abstract

There has been an ongoing debate about whether water enhances or hinders π−π stacking, a phenomenon crucial in various biological and chemical systems. In this study, the influence of water on π−π stacking is investigated by microwave spectroscopic observation of gas-phase hydrated clusters of thiophene dimers. Two isomers of (C 4 H 4 S) 2 -H 2 O and two isomers of (C 4 H 4 S) 2 -(H 2 O) 2 have been unambiguously identified. These identifications are supported by quantum chemistry calculations and isotopic measurements. In each of these conformations, water molecules are situated between aromatic pairs, forming distinctive interactions. Water molecules engage with thiophene molecules either as hydrogen bond donors through OH•••π interactions or as hydrogen bond acceptors through CH•••O interactions. The energy decomposition analysis indicates that the bonding pattern of water molecules significantly affects the π•••π interactions between aromatic rings. These findings offer valuable structural insights into the role of water in shaping π−π stacking.

Rotational spectroscopy of methyl tert-butyl ether with a new Ka band chirped-pulse Fourier transform microwave spectrometer

“…In addition, the intrinsically narrow Doppler widths achievable at low frequency allows for resolution of small splittings arising from large-amplitude motion and intramolecular interactions. 2–8 CP techniques are routinely used to study systems of fundamental interest such as clusters, 9–12 radicals, 13 and astrochemically-relevant species, 14 often in conjunction with a high-resolution, narrow-bandwidth cavity FTMW spectrometer in the centimeter band. In such investigations, the CP spectrum of the system of interest is directly compared against a predicted spectrum from quantum chemical calculations to yield a quick initial fit of experimental spectroscopic constants, followed by targeted measurements with a cavity instrument to explore small splittings as needed.…”