Halo-solvatochromism

The addition of electrolytes (ionophores) to solutions of (44) causes hypsochromic shifts of its solvatochromic absorption band [197, 209-213]. This phenomenon can be designated as halo-solvatochromism ) For example, the addition of KI, Nal,... 

These spectral changes may be ascribed to variations of solute-solvent interactions, when a given factor (solvent, temperature, or added salt) is changed. Because these are related processes, it is not uncommon for a solvatochromic compound to also show a thermochromic or halo-chromic behavior. 

There has been a review commentary of substitutions in non-polar media addressing the question, are weak interactions responsible for kinetic catalytic behaviour in 5 NAr reactions A kinetic study of the reactions of picryl fluoride with alcohols in carbon tetrachloride shows that the order in alcohol is greater than unity. This is interpreted as evidence for specific interaction between the substrate and alcohol prior to rate-limiting reaction with a further alcohol molecule. Self-association of amine molecules to form dimers which act as the effective nucleophile is an alternative explanation for the high kinetic orders observed in non-polar solvents. Results for the reaction of l-chloro-2,4-dinitrobenzene with aromatic amines in toluene - " and in benzene-hexane mixtures have been interpreted on this basis. Rate constants have been measured for reactions of l-halo-2,4-dinitrobenzenes with primary and secondary amines in a variety of aprotic binary solvent systems and correlations have been attempted with solvatochromic data, including t(30) values. ... 

Solvatochromism (12, 13). In solvatochromism the dissolution of a substance is accompanied by color formation, but the cause is not the formation of salts. On the other hand, if strongly colored salts are formed under the influence of mineral or Lewis acids, the process is called halo-chromism. The difference between the two phenomena is also apparent in the changes of the type of absorption spectra. In the case of halochromism absorption curves are radically changed (old bands disappear and new ones are formed), but in the case of solvatochromism the character of absorption curves is usually unchanged, and they are only shifted (as a whole) to shorter or longer wavelengths. Halochromism will be treated below. 

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