Bromonaphthalene color

Carbon-halogen bond cleavage in aryl halides is believed to involve initial excitation into an upper singlet state that is stable with respect to cleavage, followed by intersystem crossing to an upper triplet state that is either dissociative itself or can cross to an upper dissociative (a, a ) triplet [65-67]. The two-color approach has been used to demonstrate directly that excitation to an upper triplet state results in carbon-halogen cleavage. For example, in 2-bromonaphthalene (81) and 9-bromo-phenanthrene (82) [68], promotion of Tj to an upper triplet by dye laser excitation... 

In some cases, the paper is made transparent by immersion in organic mixtures of known refractive index (e.g., paraffin oil-bromonaphthalene, anisol). The transparent paper is then placed between two glass plates and absorption of the colored region is measured by a densitometer, which gives an idea about the quantity of the resolved component. 

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