Indirect thermochromic systems

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

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... 

Although, in theory, intrinsically thermochromic compounds should be the materials of choice for many apphcations, in practice, with the major exception of thermotropic liquid crystals (see Chapter 5, section 5.2.2), they often require quite high temperatures to effect the change, and this has limited their use. Additionally, there is also a problem with synthesising compounds to cover the desired colour gamut across the visible spectrum. Consequently, indirect systems, in which the chro-mophoric material reacts to changes in its environment brought about by heat, have... 

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). 

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