Conformational Isomerization of bis-(4-HYDROXYPHENYL)METHANE in a Supersonic Jet Expansion, Part i: Low Barrier Potential Energy Surface in the S_{0} State.

Details Conformational Isomerization of bis-(4-HYDROXYPHENYL)METHANE in a Supersonic Jet Expansion, Part i: Low Barrier Potential Energy Surface in the S_{0} State. Conformational Isomerization of bis-(4-HYDROXYPHENYL)METHANE in a Supersonic Jet Expansion, Part i: Low Barrier Potential Energy Surface in the S_{0} State.

Jun 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009mss..confemf05r&link_type=abstract

"International Symposium On Molecular Spectroscopy, 64th Meeting, Held 22-26 June, 2009 at Ohio State University. http://molspec

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The bichromophore bis-(4-hydroxyphenyl)methane, has been studied using single, double and triple resonance laser based spectroscopic methods in a supersonic jet expansion. This molecule consists of two identical chromophores (phenol moieties) linked through a methylene group with torsional flexibility along the two Ph-CH_{2} bonds. Existence of three conformational isomers in the jet expansion has been established using fluorescence excitation spectroscopy, UV-UV holeburning and fluorescence dip IR spectroscopic methods. S_0-S_1 electronic origins of the three conformers are within 25 wn (0.3 kJ/mol) of one another, with the red most origin at 35184 wn. Direct experimental determination of the isomerization barriers separating the three conformers were probed using stimulated emission pumping-population transfer spectroscopy. Experimental barriers between conformations are remarkably low, with a highest barrier of no more than 45 wn (0.54 kJ/mol) from the zero-point level. Quantum chemical calculations carried out using density functional theory (B3LYP/6-311G**) also support the three minimum energy conformations with near-identical stabilities. The calculated potential energy surfaces of the ground state along the phenyl torsional coordinates show that the minimum energy pathways to isomerization lie along the asymmetric phenyl torsional vibrational mode. Furthermore, the predicted torsional energy barriers are comparable in size to the experimentally determined thresholds.

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