Acrolein: Spectroscopy, Photoisomerization, and Theoretical Considerations

The quantum yields of fluorescence ${\mathrm{(\phi }}_F\text{\hspace{0.17em}∼\hspace{0.17em}0.007)}$ and phosphorescence ${\mathrm{(\phi }}_P\text{\hspace{0.17em}∼\hspace{0.17em}0.00004)}$ indicate that excitation results in nearly complete internal conversion and/or photochemistry. Theoretical calculations have been made including the potential energy curves resulting from twisting around the central carbon–carbon single bond as well as the terminal carbon–carbon double bond. It appears that photoisomerization cannot occur around the single bond in either the $\pi$ , $\mathrm{\pi *}$ or $n$ , $\mathrm{\pi *}$ states but could occur around the double bond in the lowest $\pi$ , $\mathrm{\pi *}$ triplet state. In the latter case, a potential energy minimum exists near 90° and degeneracy occurs with the ground state. Based on the spectroscopic and theoretical considerations herein reported, an analysis is made of the published spectroscopic results of conjugated keto steroids.