Kozo Inuzuka

Acrolein: Spectroscopy, Photoisomerization, and Theoretical Considerations

The quantum yields of fluorescence (φF ∼ 0.007) and phosphorescence (φP ∼ 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 π, π* or n, π* states but could occur around the double bond in the lowest π, π* 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.

Mechanism of Photoisomerization in the Retinals and Implications in Rhodopsin

ALL-trans and 11-cis retinals play important parts in the visual process because of the existence of the 11-cis polyene in rhodopsin. Spectroscopic studies of these show that there is weak emission from all-trans retinal and very little from the 11-cis isomer1. Also, rhodopsin shows only a very weak emission2. It is very important to develop a theoretical understanding of these results as well as of the nature of the excited states and their change as a function of the angle of twist around the 11–12 bond of the cis isomer.