Probing the Adsorption Behavior of 4,5-Diazafluoren-9-one and Its Schiff Base Derivatives on SIlver and Gold Nanosurfaces Using Raman Spectroscopy, Density Functional Theory and Potential Energy Distribution Calculations

4,5-Diazafluoren-9-one (DAFO) is an aromatic ketone synthesized by oxidizing 1,10-phenanthroline with potassium permanganate. In this present study, the Raman spectra of DAFO in the solid and solution states were recorded in the 100-2000 cm-1 spectral region using 1064, 633, 532, and 514 nm excitation sources. A normal mode analysis of DAFO was performed using density functional theory; the BLYP and B3LYP functionals, each with the 6-31G(d) and 6-311(d) basis sets were employed. The fundamental modes on the Raman spectrum of DAFO were assigned with the appropriate symmetry element using the BLYP functional and 6-31G(d) basis set. The vibrational modes were described and quantified by potential energy distribution calculations. The Raman frequencies for the solid and solution spectra were compared; the observed frequency shifts are attributed to hydrogen bonding or dipole-dipole interactions occurring between the solvent and DAFO ligand. To further assess solute-solvent interactions the UV-vis spectra of DAFO was obtained in hydrogen bonding, polar aprotic, and non-polar solvents. The fine structure of the band observed at λ max becomes more resolved as solvent polarity decreases, therefore confirming solute-solvent interactions in polar solvents.;A silver complex of DAFO was synthesized with the intent of understanding how coordination affected the Raman frequencies. The bands assigned to pyridine ring bending, ν(C=N), and ν(C=O) were shifted because of coordination. These shifts have been attributed to the molecule being perturbed because of coordination. Therefore, the Ag-DAFO complex was analyzed by X-Ray diffraction and the molecular geometries of the free and coordinated ligand were compared. The resolved crystalline structure revealed the silver ion coordinated DAFO using the lone pairs of electrons from the nitrogens in the pyridine ring. Analysis of the molecular geometry revealed the C=O bond increases in double bond character and the C5-C14 bond from the center ring was shortened because of metal-ligand coordination. These observations are correlated to the shifts in Raman frequencies; a decrease in bond length resulted in a shift to a higher vibrational energy.;The surface-enhanced Raman spectrum of DAFO was obtained on silver colloids and gold nanorods. The resulting SER spectra were compared to their corresponding normal Raman spectra, there were changes in relative band intensities and there were bands shifted because of adsorption; these observations were used to probe orientation. Orientation is determined by applying surface selections rules developed by both Creighton and Moskovits. The rules indicate, when the vibrational modes assigned to out-of-plane modes are observed as enhanced in the SER spectrum, the ligand is considered parallel relative to the metal surface, and when the vibrational modes assigned to in-plane modes are observed as enhanced, the ligand is not parallel relative to the metal surface. The relative surface enhancement factors were calculated by normalizing the spectra and then by taking the ratio of ISERS/INR. Based on the enhancement factors, the bands assigned to in-plane modes exhibited the highest enhancement factors on the Au and Ag SER spectra. This observation suggests that DAFO is not parallel to the metal nano-surfaces.;In the Ag SERS spectrum the bands with the highest enhancement factors were assigned to quadrant ring stretching and cyclopentone bending. Analysis of the carbonyl stretching frequency on the Ag spectrum revealed the frequency shifted to a lower vibrational energy. This shift has been ascribed to the carbonyl bond losing double bond character, which permits the interaction between the metal and the carbonyl oxygen. It was proposed the DAFO ligand is sandwiched between the silver hydrosol. The TER spectrum of DAFO was obtained; analysis of the spectrum revealed similarities to the Ag SERS spectrum. The carbonyl stretching frequency was lowered, the bands assigned to C=N vibrations were enhanced, and the frequencies assigned to ring bending vibrations were blue shifted, all indicative of a non-parallel orientation. DFT calculations were used to support the Ag SERS/TERS orientation. The frequencies calculated for a metal-ligand-metal sandwich reproduced the experimentally obtained data. (Abstract shortened by UMI.).