Surface-enhanced Raman spectroscopy and density functional theory study on 4,4'-bipyridine molecule.

Area of Science:

• Computational Chemistry
• Spectroscopy
• Materials Science

Background:

• 4,4 -bipyridine (BPE) is a versatile organic compound with applications in coordination chemistry and materials science.
• Understanding the molecular structure and vibrational properties of BPE is crucial for its effective utilization.
• Spectroscopic techniques provide valuable insights into molecular vibrations and surface interactions.

Purpose of the Study:

• To investigate the molecular geometry and vibrational frequencies of 4,4 -bipyridine (BPE) using computational methods.
• To record and assign the vibrational spectra of BPE using Fourier transform infrared (FT-IR), Fourier transform Raman (FT-Raman), and near-infrared surface-enhanced Raman scattering (NIR-SERS).
• To determine the orientation of BPE molecules on a silver foil substrate using surface selection rules.

Main Methods:

• Density Functional Theory (DFT) calculations with the B3LYP functional and 6-31++G(d,p) basis set were employed for geometry optimization and frequency calculations.
• FT-IR, FT-Raman, and NIR-SERS spectra of BPE on a silver foil substrate were recorded.
• Band assignments were performed based on the DFT calculations, and surface selection rules were applied to infer molecular orientation.

Main Results:

• The DFT calculations provided optimized geometric parameters (bond lengths and angles) for BPE.
• Experimental vibrational spectra (FT-IR, FT-Raman, NIR-SERS) were successfully recorded and assigned.
• The vibrational frequencies obtained from DFT calculations showed good agreement with the experimental results.
• NIR-SERS spectra exhibited differences when excited by different laser lines, attributed to enhanced chemical (CHEM) effects.
• The orientation of BPE on the silver surface was inferred from surface selection rules, with specific frequencies sensitive to structural changes.

Conclusions:

• DFT calculations are reliable for predicting the structural and vibrational properties of BPE.
• Spectroscopic techniques, particularly NIR-SERS, provide valuable information about BPE on surfaces.
• The study elucidates the molecular orientation and surface interactions of BPE on silver, contributing to its application in surface-sensitive techniques.