Ionochromic materials

Typically the chromophores used are pH sensitive, i.e. acidochromic or ionochromic (see section 1.4), and the medium is one whose pH varies with temperature. A variety of pH sensitive chromophores are known that are readily synthesised and can be modified to provide a wide range of shades. Application of these pH sensitive dyes in pressure and thermally sensitive papers for digital printing, e.g. fax papers, where the whole object is for the process to be irreversible, will be covered under ionochromism. The main area of application for reversible indirect thermochromic materials is as thermochromic organic pigments, as will be described below (section 1.3.4.1). 

Marsella, M.J., R.J. Newland, and T.M. Swager. 1995. The ionochromic response of crown ether and calix[4]arene substituted polythiophenes Towards chemoresistive sensory materials. Polym Prep... 

Chemichromism characterizes materials that are able to change their optical properties when their chemical environment changes. In particular, it includes ionochromism, halochromism and solvatochromism. 

Polythiophenes are not only interesting because of their electrical properties. On oxidation (p-doping), the electrical conductivity can be enhanced from about 10 S.cm (pristine material) up to several thousand S.cm in the oxidized form. This layers of polythiophenes are also of interest due to their large number of special electrophysical properties Thermochromism, electrochromism, solvatochromism, ionochromism, color changes under pressure and effected by electricity. 

Many experimental results have suggested that the conformational modification of the polythiophene backbone can be induced through order-disorder transitions of the side-chains [59]. It was then postulated that various external stimuli could pertuib the side-chain organization and consequently induce some chromic effects. These side-chain transitions can be induced by heating (thermochromism), varying the solvent quality (solvatochromism), ion complexation (ionochromism), photo-induced isomerization (photochromism) and affinity binding (affinity or biochromism) giving rise to a novel class of field responsive materials. 

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