Reversible Coloring/Decoloring Reactions of Thermochromic Leuco Dyes Controlled by a Macrocyclic Compound Developer

In this study, we examine macrocyclic compounds to determine whether they can provide a safer replacement and stable complex for BPA in thermochromic dyes. To achieve this objective, a series of macrocyclic compounds, Methyl- N -benzylhexahomo-triazacalix[3]arene ( MeAC3 ), p -Chloro- N -benzylhexahomo-triazacalix[3]arene ( ClAC3 ), α-Cyclodexdrin ( a-CD ), β-Cyclodexdrin ( β-CD ). p -tert-Butylthiacalix[4]arene ( TC4 ), Calix[4]arene ( C4 ) and Resorcin[4]arene ( RC4 ) were synthesized. Among these macrocyclic compounds, RC4 was determined to be the most appropriate candidate to replace BPA as the developer material used in thermochromic dyes. In tests of prepared thermochromic dyes, RC4 had results similar to those of BPA, achieving the best protonation/deprotonation equilibria and providing a dark contrast with the thermochromic dye. DFT calculations also showed stable complexes between RC4 and CVL via hydrogen-bond interactions.