Knowledge Bank

No fluorescence has ever been observed from any aromatic ketone in the acetophenone and benzophenone series. It is presumed that a highly efficient intersystem crossing mechanism must exist between the lowest $\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}n\pi \ast$ state and the triplet manifold. The presumed rate of this process is anomalously high. Observables such as comparative line widths, and the variation of the phosphorescence lifetime with temperature in the range of $4.2\circ K$ provide new information on the intersystem crossing mechanism is condensed media. Experimental results on linewidths and temperature effects will be presented in relation to a number of ketones representing a variety of electronic structural types.