Thermochromic materials
AssigneePolaroid Corporation
InventorsMarcis M. Kampe, David P. Waller, David C. Whritenour
Life of this patent
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Abstract
Disclosed is a class of bridged phthalides and sulfinate esters which exhibit reversible thermochromism. At room temperature and in the presence of base, these compounds are substantially colorless but upon the application of heat they become colored, reverting to their original colorless or weakly colored state upon cooling. This colorless to colored, temperature-dependent cycle can be repeated many times. These compounds have utility as temperature sensors and as thermal pH indicators.
Claims18
A thermochromic material, comprising:
- (a) a compound containing the thermochromic system represented by the formula ##STR16## wherein R.sub.1 represents a group which exerts a steric influence such that the lactone or sulfone would remain closed at room temperature but upon the application of heat would overcome said steric influence so that ring opening could occur;
- and
- (b) a basic component providing a pH at or above the pka of said compound;
- said thermochromic material being characterized in that it goes from a substantially colorless state at room temperature to a more intensely colored state upon heating to an elevated temperature and returns to its substantially colorless state upon subsequent cooling to room temperature.
A compound of the formula ##STR19## wherein R.sub.1 represents a group which exerts a steric influence such that the lactone or sulfone, when said compound is at a pH at or above its pKa, remains closed at room temperature but upon the application of heat overcomes said steric influence so that ring opening and hence color formation occurs;
- R.sub.2, R.sub.3, R.sub.4, R.sub.5 and R.sub.6 each independently represents hydrogen, substituted or unsubstituted alkyl, substituted or unsubstituted aryl, alkoxy, halo, carboxy, or hydroxy, further providing that at least one of R.sub.2 and R.sub.3 are hydrogen.
Dependencies are inferred from the claim text.