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Solvent, isotope, temperature and structural effects upon the absorption and emission spectra of salicylic acid derivatives have been recorded. In all cases, the emission in non-polar media, if observed, was fluorescence which was abnormally Stokes shifted, the magnitude of the shift being directly proportional to the basicity of the carbonyl group. When $R=H$ or phenyl, no emission was observed, even at $4.2\circ K$ . This appears due to a low-lying $\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}n\pi \ast$ state which allows smooth correlation to a non-emitting quinoid tautomer. In cases where the $\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}n\pi \ast$ state is lowest, the proton transfers to a point where the excited state is best described as $\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}n\pi \ast$ associated with the quinoid form. Antibonding activity about the $C1-C7$ bond gives rise to cis-trans isomerization, competitive with emission from the planar form. Semiempirical MO schemes $(CNDO/2,CNDO/S,Pariser-Parr-Pople,HMO)$ have been used to study the coordinate displacements of acetylacetone and salicylic acid derivatives in the ground, $n\pi \ast$ and $n\pi \ast$ states. One and two dimensional energy surfaces, along with changes in bond order and charge density, were recorded for proton motion within the plane of these molecules. The results were used to interpret the spectroscopic and photochemical results obtained by us and previous workers.