ethylamino-2-hydroxychalcone in toluene, and colored species undergoing dark reaction to regenerate trans-isomer may be ascribed to cis-isomer with the lifetime of 77 min at room temperature. It is demonstrated that a trans→cis isomerization in the lowest triplet state is significantly responsible for the primaryprocess of the coloration.
Flavyliumsalts exhibited a reversible thermochromism in an agar-gel matrix. Thus, by the temperature change from −3 to 50 °C, the absorption band around 600 nm of 7-diethylamino-4′-dimethylaminoflavylium perchlorate increased by a factor of ca. 1.5, while the band around 520 nm substantially decreased. Upon repeated cycles of the color change no significant fatigues were observed. The thermochromic