Indirect reversible thermochromic

A technically more appropriate approach is to separate reversible organic thermochromism into intrinsic systems, where heat is the sole cause of the colour change, from indirect systems, in which the colour variation involves changes in... 

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). 

A technically more appropriate approach would be to diversify the reversible organic thermochromism of intrinsic systems, in which heat is the only factor influencing the colour change, from the indirect systems in which the colour change is induced by the heat that affects the surroundings of the chromophore (Burkinshaw et al., 1999). 

The main application area for these indirectly thermochromic, reversible systems is the manufacture of organic thermochromic pigments. 

---