Ultraviolet and Visible Light Absorption Spectroscopy

From the beginning of research into retinoids, absorption spectroscopy has been employed as an aid in the characterization of structure (Zechmeister, 1962 Vetter et aL, 1971), and the principles and possible applications of this spectroscopic method have been discussed in detail in review articles (Drujan, 1971 Ottolenghi, 1980). It has proved particularly useful in the investigation of the protein pigments rhodopsin and bacteriorhodopsin (Honig and Ebrey, 1974 Honig et aL, 1975 Honig, 1978 Stoeckenius et aL, 1979). 

The absorption spectrum of retinaldehyde (2) in the visible and near-ultraviolet region shows three bands a main one at about 370 nm and two weaker transitions at 280 nm and 250 nm. It has been concluded from a number of theoretical calculations that the main 370-nm band in all geometric isomers of retinaldehyde (2) is attributable to the allowed transition in the lowest state (Wiesenfeld and Abrahmson, 1968 Langlet et aL, 1969a Christensen and Kohler, 1973 Schulten et a/., 1976). 

The relatively low extinction observed for (1 lZ)-retinaldehyde (377) has been the subject of theoretical treatment (Honig and Karplus, 1971 Ottolenghi, 

Both conformations of (1 lZ)-retinaldehyde (377) are highly twisted, so that it is difficult to apply the simple rules for making spectroscopic assignments to (377). At room temperature, the order of intensities for the main (a) band of retinaldehydes is as follows all- 13Z 9Z IIZ (Honig et al., 1980). 

The absorption spectra of 3,4-didehydroretinaldehydes are very similar to those of retinaldehydes (von Planta et al, 1962 Morton, 1972), whereas the spectra of retinaldehyde Schiff bases are very similar to those of the aldehydes from which these compounds are derived (Schaffer et al, 1974 Sandorfy, 

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Ultraviolet and visible light absorption spectroscopy can be used to identify chromophores (e.g. benzene rings and carbonyl groups) and to determine the lengths of sequences of conjugated multiple bonds in polymers. It also can be used to analyse polymers for the presence of additives such as antioxidants or for detection of residual monomer(s). Additionally, fluorescence and phosphorescence techniques are important in studies of polymer photophysics. 

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