# HIGH RESOLUTION FLUORESCENCE EXCITATION SPECTROSCOPY OF THE MONOMER AND DIMER OF 2-PYRIDONE

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 Title: HIGH RESOLUTION FLUORESCENCE EXCITATION SPECTROSCOPY OF THE MONOMER AND DIMER OF 2-PYRIDONE Creators: Held, A.; Champagne, B. B.; Pratt, D. W. Issue Date: 1992 Publisher: Ohio State University Abstract: Rotationally resolved fluorescence excitation spectra of two vibronic bands in the $S_{1}\leftarrow S_{0}$ electronic transition of 2-hydroxypyridine (2HP), and of the corresponding bands in the hydroxy-deuterated molecule, have been obtained. A comparison of the rotational constants of the two molecules shows that the two bands both originate in the zero-point vibrational level of the planar keto tautomer of 2HP, 2-pyridone (2PY), and terminate in different zero-point levels of 2PY that have different out-of-plane equilibrium geometries at nitrogen. Additionally, all four bands exhibit ""anomalous"" rotational line intensities that are shown to result from an in-plane inertial axis reorientation which occurs on absorption of the photon. The rotationally resolved $S_{2}\leftarrow$ $S_{0}$ electronic spectrum of the dimer of 2PY, $(2PY)_{2}$, was recorded $-945 cm^{-1}$ to the blue of the first monomer origin. Structural information derived from the spectrum shows that the protonated dimer has a doubly hydrogen bonded planar $C_{2h}$ structure in its $S_{0}(^{1}A_{g})$ and $S_{2}(^{1}B_{u})$ states. Analogous studies of $(2PY)_{2}-d_{1}$ and $(2PY)_{2}-d_{2}$ show that $(2PY)_{2}$ and $(2PY)_{2}-d_{2}$ are energy delocalized dimers in their $S_{2}$ states. A comparison of the effective and substitution structures of $(2PY)_{2}$ shows that there is a distortion of the hydrogen bonded geometry when hydrogen is replaced by deuterium. These structural changes will be discussed. Description: Author Institution: Department of Chemistry, University of Pittsburgh URI: http://hdl.handle.net/1811/12704 Other Identifiers: 1992-MG-02