RAMAN AND SURFACE ENHANCED RAMAN SPECTRA OF 7-HYDROXYFLAVONE AND 3’,4’-DIHYDROXYFLAVONE

The FT-Raman and surface-enhanced Raman (SER) spectraof two hydroxyl derivatives of flavone, namely 7-hydroxyflavone,3’,4’-dihydroxyflavone, have been obtained. Theimportance of these compounds lies in the fact that theyare simple precursors to the most impor tant of theflavonoid dyes, such as quercetin. The SERS spectra wereobtained on citrate reduced Ag colloids. Assignments ofthe experimentally obtained normal vibrational modes wereaided by density functional theory (DFT) calculations usingthe B3LYP functional and the 6-31+G* basis set. Excellentfits were obtained for the observed spectra with little scaling.As in other flavone derivatives, the C=O stretchingbands in the SERS spectra are diminished in intensity byproximity of the metal surface relatively compared to thenormal Raman spectra. Additionally, the lines at lowerwavenumbers, assigned to in-plane ring deformation, arestrongly enhanced by the surface, indicating a perpendicularorientation of the flavonoids on the Ag surface. Finally,the influence of the 7 and 3’,4’ OH substitutions on thespectra of chrysin, apegenin, and luteolin are examined.