Time Resolved Surface Enhanced Raman Scattering Studies of 3-Hydroxyflavone on a Ag Electrode

Abstract

Reverse proton transfer (RPT) of 3-hydroxyflavone (3-HF) from the tautomer ground state to normal ground state has been studied by time-resolved surface enhanced Raman scattering (TRSERS) in aqueous solution in the presence of oxygen. The tautomer ground state of 3-HF is formed by an exciting 337 nm nitrogen laser pulse and monitored by a 488 nm Ar + laser with gated photodiode array detection. B3LYP DFT calculations with 3-HF bound to the apex adatom of a Ag 20 cluster model show that a tilted orientation of the molecule with respect to the surface site is reasonable and is consistent with the SERS spectral characteristics. The geometry optimized structures also show that a cyclic monohyrate, 3-HF(H 2 O), species is stable from which biprotonic PT could take place. By studying the changes of some transient band intensities with time, the lifetime of tautomer 3-HF on a Ag electrode is determined to be 1.4 µs. Besides the photoinduced photooxygenation product, evidence for an additional endo-peroxide intermediate is obtained.

Application of Raman Spectroscopy, Surface-Enhanced Raman Scattering (SERS), and Density Functional Theory for the Identification of Phenethylamines

“…It has the power to provide excellent values for normal-mode vibrational frequencies and intensities. In recent studies, 33–35 we have found that DFT software provides reliable and accurate ways of predicting and assigning the Raman bands of various dye molecules. Density functional theory has grown in popularity in computational chemistry because the calculations provide much better agreement with experimental values than the Hartree–Fock procedures.…”

Surface-enhanced Raman Spectroscopy for Trace Identification of Controlled Substances: Morphine, Codeine, and Hydrocodone

“…DFT has the power to provide excellent values for normal mode vibrational frequencies and intensities. In recent works (15–18), we have found that DFT gives reliable and accurate way to predict and therefore to assign the Raman bands of various dye molecules. DFT has grown in popularity in computational chemistry because the calculations provide much better agreement with experimental values than the Hartree–Fock procedures (19).…”

The kinetics and mechanism of photooxygenation of 4′-diethylamino-3-hydroxyflavone

“…The transition states and intermediates of the photooxidation of D were characterized with the help of potential energy surface (PES) calculations. A reaction path analogous to the experimentally established steps of the photooxidation of the parent compound, 3HF, [23][24][25][26][27] was considered. The results are illustrated in Fig.…”