Solvatochromism and the solvation structure of benzophenone

Abstract

Many complex molecular phenomena, including macromolecular association, protein folding, and chemical reactivity, are determined by the nuances of their electrostatic landscapes. The measurement of such electrostatic effects is nonetheless difficult, and is typically accomplished by exploiting a spectroscopic probe within the system of interest, such as through the vibrational Stark effect. Raman spectroscopy and solvatochromism afford an alternative to this method, circumventing the limitations of infrared spectroscopy, providing a lower detection limit, and permitting measurement in a native chemical environment. To explore this possibility, the solvatochromism of the C=O and aromatic C-H stretching modes of benzophenone are investigated using Raman spectroscopy. In conjunction with density functional theory calculations, these observations are sufficient to determine the probe electrostatic environment as well as contributions from halogen and hydrogen bonding. Further analysis using a detailed Kubo-Anderson lineshape model permits the detailed assignment of distinct hydrogen bonding configurations for water in the benzophenone solvation shell. These observations reinforce the use of benzophenone as an effective electrostatic probe for complex chemical systems.

Molecular dynamics and simulations study on the vibrational and electronic solvatochromism of benzophenone

“…These observations are in very good agreement with previous work by Hackett and co-workers. 43 The C= =O stretching frequency in different solvents of varying polarity and their various solvatochromic parameters are tabulated in Table I. Hereafter, C==O stretching in aprotic solvents will be indicated as v 6a , while the lower and higher C= =O stretching frequencies in protic solvents will be indicated as v ′ 6a and v ′′ 6a , respectively.…”

“…42 Recently, Hackett and coworkers have utilized the >C= =O stretching frequency as a solvent polarity marker using Raman spectroscopy in conjunction with Density Functional Theory (DFT) calculations and discussed its application as an electrostatic probe for protein and complex environments. 43 In this study, we have utilized Raman spectroscopy and computer simulations invoking a supramolecule embedded in a polarizable-continuum solvent model to gain insight into the solute-solvent interactions at the microscopic level. The supramolecule configurations were generated by classical molecular dynamics simulations (c-MDSs), adopting the Optimized Potentials for Liquid Simulation-All Atoms (OPLS-AAs) force fields developed by Jorgensen and coworkers.…”

Electrostatic Interactions Are Key to C═O n-π* Shifts: An Experimental Proof

“…CO stretching frequencies have also been reported to show linear sensitivity with similar semiempirical expressions for aprotic solvents . Other semiempirical polarity parameters/scales like Kosower’s Z scale and Onsager reaction field have been extensively used to correlate the solvent effects on n-π* and CO stretching frequencies; , however, H-bonding pose a challenging task to describe solute–solvent interactions. The continuum semiempirical models do not account for the microscopic nature of the solvent and thereby cannot describe specific chemical interactions like H-bonding.…”

“…CO stretching frequencies have also been reported to show linear sensitivity with similar semiempirical expressions for aprotic solvents. 19 Other semiempirical polarity parameters/ scales like Kosower's Z scale and Onsager reaction field have been extensively used to correlate the solvent effects on n-π* and CO stretching frequencies; 20,21 between IR shift (ground electronic state phenomenon) and nπ* shift (involves both ground and excited states) would provide model-free direct experimental evidence of the role of ground-state electrostatic interactions toward the solvatochromic blue shifts observed for carbonyls (Figure 1A). Incorporating both protic and aprotic solvents in our study will enable us to confirm if electrostatic interactions are key toward the spectral shifts in both H-bonding and non-Hbonding solvation environments.…”

New Insights into Quinine–DNA Binding Using Raman Spectroscopy and Molecular Dynamics Simulations

“…This effect arises from the fact that the local environment exerts an electric field onto a chromophore, altering its vibrational transition energy in a manner that depends on the difference in the dipole moments of the ground and first excited vibrational states. Recent work by the Boxer group − and others − show that the frequency variation of some vibrational probes, such as carbonyls, ,, are well described by the vibrational Stark effect. However, the solvatochromic trends of other probes, such as nitriles, ,− cannot be understood solely on the basis of electrostatics due to substantial quantum mechanical effects on the vibrational frequencies.…”