Electron-withdrawing substituents carbonyl and nitro compounds

3 Electron-withdrawing substituents carbonyl and nitro compounds 

The fluorescence properties of aromatic carbonyl compounds are complex and often difficult to predict. 

Many aromatic aldehydes and ketones (e.g. benzophenone, anthrone, 1- and 2-naphthaldehyde) have a low-lying n-n excited state and thus exhibit low fluorescence quantum yields, as explained above. The dominant de-excitation pathway is intersystem crossing (whose efficiency has been found to be close to 1 for benzophenone). 

Some aromatic carbonyl compounds have a low-lying n-n excited state and thus have a reasonable quantum yield (e.g. 0.12 for fluorenone in ethanol at 77 K and 0.01 at room temperature). However, if an n-n state lies only slightly higher in energy, the fluorescence quantum yield strongly depends on the polarity of the 

It should be mentioned that many nitroaromatics undergo photodegradation. For instance, 9-nitroanthracene is transformed into anthraquinone upon illumination. 

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