A Novel Supramolecular Multicolor Thermometer by Self-Assembly of a <i>π</i>-Extended Zinc Porphyrin Complex

A zinc complex of (3-pyridyl)porphyrin with an alkynyl sidearm (1) preferentially formed a cyclic tetramer in toluene, which showed supramolecular thermochromism at ambient temperatures of 0−100 °C. Because of an appropriate extension of π-electronic conjugation of the porphyrin chromophore, the thermal-induced self-assembling dynamics of 1 can be detected as a vivid color change from red to yellow to green. In sharp contrast, 2 without any alkynyl group, on heating, developed only a small color change from orange to pink, while 3 bearing two alkynyl groups stayed green and did not display any thermochromism.