Cationic and anionic halochromism

Abstract

The spectral changes of organic solutions of N,N,N′,N′‐tetramethylenediaminoacetylacetonatocopper(II) perchlorate and a merocyanine dye in the presence of NaI or LiClO4 provide examples of anionic and cationic halochromism, respectively. The observed changes are interpreted as arising from all possible interactions in the three‐component system of the dye, the salt and the solvent.

The effect of annulation upon the solvatochromic behaviour of related merocyanines

“…The solvatochromic behaviour of pyridinium phenoxide dyes reflects to a major extent the microenvironment around the phenoxide moiety of the molecule 13 , the ET(30) dye being one of the most conspicuous examples of this. Therefore, in mimicking polarity changes around systems like 1, we simply positioned a "sparkle" of charge +2 along the C-O bond of the phenoxide ring, at a variable distance from the oxygen atom.…”

The cationic halochromism of phenolate betaines: Molecular dynamics and quantum mechanics studies

“…Merocyanine 2 has been the subject of investigation of various research groups [13,14] since it was first described by Brooker et al [15,16]. Like dye 1, it is a classic example of a dye that exhibits cationic halochromism [5]. The 1-methyl-8-oxyquinolinium dye 3 was originally described by Ueda and Schelly [17].…”

“…In the latter case, the CI ZINDO/S excitation energies were practically the same, irrespective of the method employed for the optimisation. The experimental data [5] for the halochromic behaviour of merocyanine 2 in acetonitrile, in the presence of increasing concentrations of LiClO 4 and NaI, are shown in Fig. 4b.…”

“…We have been interested for some time in the study of the latter type of halochromism, and have distinguished a cationic and an anionic halochromism [5], depending on the nature of the added species responsible for the halochromic shifts in solution. Examples of cationic halochromism are found in solutions of solvatochromic phenolate dyes [6][7][8].…”

Syntheses and UV/Vis-Spectroscopic Properties of Hydrophilic 2-, 3-, and 4-Pyridyl-Substituted Solvatochromic and Halochromic PyridiniumN-Phenolate Betaine Dyes as New Empirical Solvent Polarity Indicators

“…Furthermore, the genuine halochromism of a solvatochromic probe dye can be preferentially anion-or cation-dependent. [97] In some exploratory measurements, we have studied the Vis-spectral behavior of aqueous solutions of the new hydrophilic betaine dye 8 on addition of alkali metal halides, urea, and tetramethylammonium chloride (see Table 5). According to Entries 1Ϫ5 in Table 5, addition of alkali metal chlorides to aqueous solutions of dye 8 always results, with increasing salt concentration, in small hypsochromic band shifts.…”