Phosphorescence excitation and emission spectra of 2hyphen;indanone single crystal have been observed at 1.5 K. The lowest triplet stateT1is of pgr;ast;larr;ncharacter which is localized in the carbonyl moiety. The very weak 0ndash;0 band is located at 28thinsp;853 cmminus;1. The molecule is pyramidally distorted like formaldehyde and has an active outhyphen;ofhyphen;plane C=O wagging mode. The barrier height to inversion (V) and the C=O bend angle at the potential minimum (thgr;m) have been determined to be 883 cmminus;1and 37deg;, respectively. This distortion is consistent with the previous ODMR results. Fluorescence excitation spectrum of 2hyphen;indanone has also been observed using a pulsed supersonic nozzle beam technique. The lowest excited singlet state is also of pgr;ast;larr;ncharacter localized in the carbonyl moiety. The 0ndash;0 band is relatively intense and located at 30thinsp;664 cmminus;1. We obtainedV=1006 cmminus;1and thgr;m=37deg; for theS1state. The spectroscopic results andabinitiocalculation show that theS1andT1states of 2hyphen;indanone are very similar to those of cyclopentanone. The difference between the spectral features of theT1andS1transitions is explained by the symmetry lowering of the molecule and by the vibronic coupling with a higher excited state.
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