The fluorescence quantum yield of vitamin A2.

The fluorescence quantum yield of all-trans 3,4-didehydroretinol (vitamin A2) was measured in hexane at room temperature, using quinine sulfate as a standard. Unlike all-trans retinol (vitamin A1) which possessed a relative quantum yield of 0.0298, 3,4-didehydroretinol was 37 times lower in fluorescence (i.e. 0.0008). In addition, a significant bathochromic shift (both excitation and emission maxima) and a general broadening of the fluorescence spectra were noted for 3,4-didehydroretinol. This information is important not only for the understanding of the basic structure of vitamin A but also the photochemistry of vision.