A STUDY OF THE EXCITED ELECTRONIC STATES OF 9-FLUORENONE
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Date
1974
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Ohio State University
Abstract
Some spectroscopic properties of the low-energy electronic states of 9-fluorenone have been examined. The spectra in paraffin matrices at 4.2$^{\circ} K$ show detailed vibrational spectra. Two fluorescence spectra are observed; a diffuse emission arises from 9-fluorenone crystals In the paraffin matrix, and a sharp omission is characteristic o£ the molecule The sharp fluorescence is analyzed in terms of known a vibrational fundamentals. The sharp absorption is a near mirror-image to the fluorescence, so Herzberg-Teller vibrations are not prominent. The polarization in the crystal spectrum allows this low-energy transition near 23 000 $cm^{-1}$ to be assigned $^{1}B_{2}$ $\leftarrow$ $^{1}A_{1}$. Because there is no vibronic perturbation in fluorescence, and certainly no out-of-plane modes, $a\Pi^{*}$ $\leftarrow$ n transition seen at about 26 000 $cm^{-1}$ is tentatively assigned $^{1}B_{1}$ $\leftarrow$ $^{1}A_{1}$. Another sharp absorption system is seen at 31 000 $cm^{-1}$ in the paraffin matrices at 4.2$^{\circ} K$ (linewidth 6 $cm^{-1}$) but no fluorescence was detected. The polarized crystal spectrum indicated the assignment of this system and another very strong system at 40 000 $cm^{-1}$ to be $^{1}B_{2}$ $\leftarrow$ $^{1}A_{1}$, while other systems at about 34 000 $cm^{-1}$ and 44 000 $cm^{-1}$ are $^{1}A_{1}$ $\leftarrow$ $^{1}A_{1}$. The phosphorescence spectrum of pyrene-$d_{10}$ held in a single crystal of 9-fluorenone at 4.2$^{\circ} K$ has been recorded. No delayed fluorescence from the boat crystal is observed at 4.2$^{\circ} K$ but is intense at $77^{\circ} K$. The energy difference between host and guest triplet levels is estimated to be about $900 cm^{-1}$ allowing the lowest triplet state of 9-fluorenone to he placed at $17800 cm^{-1}$.
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Author Institution: Department of Chemistry, State University of New York; Department of Chemistry, University of British Columbia