Raman, Surface-Enhanced Raman, and Density Functional Theory Characterization of (Diphenylphosphoryl)(pyridin-2-, -3-, and -4-yl)methanol

Abstract

This work presents near-infrared Raman spectroscopy (FT-RS) and surface-enhanced Raman scattering (SERS) studies of three pyridine-α-hydroxymethyl biphenyl phosphine oxide isomers: (diphenylphosphoryl)(pyridin-2-yl)methanol (α-Py), (diphenylphosphoryl)(pyridin-3-yl)methanol (β-Py), and (diphenylphosphoryl)(pyridin-4-yl)methanol (γ-Py) adsorbed onto colloidal and roughened in oxidation-reduction cycles silver surfaces. The molecular geometries in the equilibrium state and vibrational frequencies were calculated by density functional theory (DFT) at the B3LYP 6-311G(df,p) level of theory. The results imply that the most stable structure of the investigated molecules is a dimer created by two intermolecular hydrogen bonds between the H atom of the α-hydroxyl group (in up (HOU) or down (HOD) stereo bonds position) and the O atom of tertiary phosphine oxide (═O) of the two monomers. Comparison the FT-RS spectra with the respective SERS spectra allowed us to predict the orientation of the hydroxyphosphonate derivatives of pyridine that depends upon both the position of the substituent relative to the ring N atom (in α-, β-, and γ-position, respectively) and the type of silver substrate.

Probing the Ag, Au, and Cu electrode/pyridine-α-hydroxymethyl biphenyl phosphine oxide isomer interface with SERS

“…We have demonstrated that the position of the substituent in the pyridine ring has a strong influence on the geometry of isomers on the ORC substrate. However, this effect was less pronounced for molecules adsorbed onto the colloidal surfaces [30,35]. We also showed that the SERS spectral profiles for isomers immobilized onto the colloidal Ag and Au surfaces more closely resembled those in the corresponding FT-RS spectra than those in the SERS spectra onto the ORC Ag substrate [30,35].…”

“…Because the FT-RS and SERS band assignments of the normal mode vibrations of these compounds onto the Ag and Au colloidal nanoparticles and onto the ORC Ag substrate have been previously discussed [30,35], we will not discuss this issue in detail. Instead, we focused on the analysis of the enhancement, shift in wavenumber, and band broadening of the particular spectral features that permit characterization of the geometry of the adsorbed molecules, which depends on the isomer type, the electrode material, and the applied electrode potential.…”

“…(Diphenylphosphoryl)(pyridin-2, -3, and -4-yl)methanol synthesis (Diphenylphosphoryl)(pyridine-2-yl)methanol, (diphenylphosphoryl)(pyridine-3-yl) methanol, and (diphenylphosphoryl)(pyridine-4-yl)methanol were synthesized according to a previously described methodology [27][28][29]. The specific procedure for the synthesis of these compounds has been described previously [30]. The purity and chemical structures of the samples were demonstrated by an analysis of the results from 1 H and 31 P NMR spectroscopy and electrospray mass spectrometry [30].…”

“…The specific procedure for the synthesis of these compounds has been described previously [30]. The purity and chemical structures of the samples were demonstrated by an analysis of the results from 1 H and 31 P NMR spectroscopy and electrospray mass spectrometry [30].…”

Conformational differentiation of α‐cyanohydroxycinnamic acid isomers: a Raman spectroscopic study

“…Raman spectroscopy has been used to identify structural differences, typically to differentiate isomeric pairs by taking advantage of changes in select vibrational modes . Notable examples are the work of Yenagi, et al , who used Raman spectroscopy coupled with density functional theory (DFT)‐based theoretical calculations to describe hydrogen bonding and cis‐ isomerism, trans‐ isomerism in 2‐chloro‐3‐hydroxybenzaldehyde and 3‐chloro‐4‐hydroxybenzaldehyde .…”