Color change (yellow \documentclass{article}\pagestyle{empty}\begin{document}$\rightleftharpoons$\end{document} orange) of 4,6,7‐tri(alkoxy‐substituted aryl)‐1,2,5‐thiadiazolo[3,4‐c]pyridines in the solid phase

Reversible color change of 4,6,7-tri(alkoxy-substituted phenyl)-1,2,5-thiadiazolo[3,4-c]pyridines 5 in the solid state was observed: on grinding, yellow crystals of 5 became an orange amorphous solid which, on heating or washing with an appropriate solvent, gave the original yellow crystals.