Charge-transfer surface-enhanced resonance Raman spectra of benzene-like derivative compounds under the effect of an external electric field

Abstract

The singular charge-transfer SERS spectra of symmetric and non-symmetric benzene-like compounds and their selective enhancement under electric field are investigated.

Chemical Enhancement Effect of Icotinib–Au Complex Studied by Combined Density Functional Theory and Surface-Enhanced Raman Scattering

“…In this process, the Fermi level of gold overlaps with the frontal orbital of the adsorbed icotinib molecule, which creates a chemical bond between the molecule and the metal, thereby forming a new complex. The occurrence of the charge transfer effect causes the local chemical environment of the molecule to change, the molecular polarization rate increases, and the Raman scattering cross section changes, which leads to the chemical enhancement of the Raman signal ground state of the icotinib–Au 6 complex . This enhancement effect is the chemical enhancement effect in the SERS effect, and the plasmonic effect mentioned above jointly contributes to the signal enhancement in the SERS.…”

“…The occurrence of the charge transfer effect causes the local chemical environment of the molecule to change, the molecular polarization rate increases, and the Raman scattering cross section changes, which leads to the chemical enhancement of the Raman signal ground state of the icotinib−Au 6 complex. 46 This enhancement effect is the chemical enhancement effect in the SERS effect, and the plasmonic effect mentioned above jointly contributes to the signal enhancement in the SERS. Since the molecular docking of icotinib−Au 6 complexes through ethynyl groups has the highest molecular stability, we selected the peak (1984 cm −1 ) corresponding to the C28C29 stretching vibration as the reference object for calculating the CE enhancement factor.…”

How Do Adsorbent Orientation and Direction of External Electric Field Affect the Charge-Transfer Surface-Enhanced Raman Spectra?

“…For more than 40 years, surface-enhanced Raman spectroscopy (SERS) has attracted remarkable attention as a powerful surface sensitive technique to detect trace amounts of analytes and characterize the structures from their rich vibrational spectra. − It has a wide variety of applications in chemical detections, due to the enhancement of intensities by a factor of 10 4 −10 6 or even larger by placing the molecules in hotspot positions of gold and silver nanoparticles, enabling single-molecule detection (SM-SERS). − Experimental observations have proved the ability of SERS as a structurally sensitive probe that can characterize the molecular surface configuration and adsorption orientation, all through the change in the relative intensities of measured signals. − The high sensitivity of this phenomenon comes from the effect of small changes in the polarizability on the intensities in response to radiation. Therefore, different local parameters such as the energy of the incident lights, − configuration and composition of metallic surfaces, ,− intrinsic adsorbent properties, − and also electrode potentials − can influence the overall performance and the pattern of spectra. As an example, Haes and co-workers reviewed the influence of intra- and intermolecular interactions on SERS spectral features and considered the dependence of signals on the adsorbent affinity and distance.…”

“…SERS-CT has been extensively studied as a sensitive mechanism that can present the effect of local and environmental parameters on the pattern of spectra. ,, Moreover, in tip-enhanced Raman scattering, this resonance chemical mechanism has a main role in finding the adsorption configuration and also the relative position of the tip with respect to the adsorbent. , In our previous studies, we tried to investigate the effect of variation of the external electric field, the surface element, and the adsorbent compounds on the relative intensities of SERS-CT spectra. In agreement with the experiment, we found different patterns for the same molecule at various applied potentials and also for different benzene-like derivatives at the same potential.…”

“…The amplitude and direction of the excited-state gradient vectors of this specific state can be used as a distinguishing factor to explain the intensity and pattern of spectra. In our previous studies, the validity of this approach was demonstrated for SERS-CT spectra of pyridine 30 and benzene-like derivative compounds 26 under the effect of uniform finite electric field. Herein, we try to consider the effect of changing the orientation and distance of molecular adsorption and also the direction of the external electric field on the pattern of SERS-CT spectra for pyridine on silver clusters.…”