Interaction, chromophore isolated molecule

While the factors resulting here in a given distortion are intramolecular, the conclusions we can draw may be applied to cases where an isolated molecule is distorted by its environment. We would like to examine this approach as starting point for treating the effect of the 11-cw retinal-opsin interaction on the photoisomerization quantum yield of 11-cw to aW-trans retinal. This quantum yield increases from 0.2 for the free chromophore [9] to 0.66 in rhodopsin [10]. This value is close to that of the biacetyl sensitized reaction of the free chromophore, 0.75 [11], and indicates that the triplet state is involved to a large extent in the photoisomerization of ll-cis retinal and that intersystem crossing is inefficient. 

Similarly, the spectral effects of two isolated chromophores in a molecule (separated by at least two single bonds) are, m principle, independent and are additive. Hence, in the molecule CH3CH2CNS, an absorption maximum due to the CNS group occurs at 245 nm with an e of 800. In the molecule SNCCH2CH2CH2CNS, an absorption maximum occurs at 247 nm, with approximately double the intensity (e = 2000). Interaction between chromophores may perturb the electronic energy levels and alter the spectrum. 

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