Impact of choice of alkane deposition solvent on 4-fluorobenzoic acid layers adsorbed on silver nanostructures

Evidence for Charge Transfer and Impact of Solvent Polar Properties on Aminobenzonitrile Adsorption on Silver Nanostructures

“…Since it has already been shown that the cyano group of 2ABN interacts with the SNPs, it is likely that the n -heptane forms weak C–H hydrogen bonds with the lone pair of the amino group in 2ABN. Similar C–H hydrogen bonding has been demonstrated between the carboxylate group of 4-fluorbenzoate ions and n -heptane in the multilayer in previous work. , It is likely that the close proximity of the amino and cyano groups in 2ABN will allow for one n -heptane to form C–H hydrogen bonds with both substituent groups simultaneously, thus explaining the n -heptane intercalation into the 2ABN multilayer. A formal definition of a hydrogen bond according to Pimentel and McClellan is a bond that sterically involves a hydrogen atom that is already bonded to another atom. , Along these lines, an n -heptane molecule interacting with the amino and cyano groups of 2ABN would fit this definition of a hydrogen bond.…”

“…n-Heptane was found to be a good alkane solvent in previous experiments because its evaporation rate is slow enough to allow ample time for adsorbate equilibration with the SNPs. 25 Figure 3, which is a magnification of the CN stretching region of Figure 2, reveals a dramatic shift in the maximum peak position with coverage. At the lowest exposure of 5 μL of 4ABN/n-heptane, the CN stretch is at 2221 cm −1 .…”

“…The circumstances are much different in Figure when 4ABN is adsorbed onto SNPs using n -heptane as the solvent (a solvent containing only nonpolar bonds). n -Heptane was found to be a good alkane solvent in previous experiments because its evaporation rate is slow enough to allow ample time for adsorbate equilibration with the SNPs . Figure , which is a magnification of the CN stretching region of Figure , reveals a dramatic shift in the maximum peak position with coverage.…”

“…n-Heptane was found to be a good alkane solvent in previous experiments because its evaporation rate is slow enough to allow ample time for adsorbate equilibration with the SNPs. 25 This occurs because n-heptane with nonpolar bonds solvates the 4ABN to a lesser extent than solvents such as acetone or dichloromethane with more polar bonds. As more 4ABN molecules enter the multilayer using the n-heptane deposition solvent, there is less interaction of each 4ABN molecule on average with the SNPs.…”

“…An advantage of studying the interaction of an adsorbate such as an aminobenzonitrile with silver nanoparticles (SNPs) is the amplified vibrational signal from the adsorbate in Raman and infrared spectroscopies induced by local surface plasmons associated with the SNPs. Prior work has shown that rough silver films formed by evaporating a few nanometers of silver can enhance the Raman signal of an adsorbate monolayer by ×10 5 or more, termed surface-enhanced Raman spectroscopy (SERS), while the infrared signal of a monolayer and even the multilayer of an adsorbate can be enhanced by ×50 or more (surface-enhanced infrared absorption, or SEIRA). − …”