A novel supramolecular multicolor thermometer by self-assembly of a pi-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 degrees C. Because of an appropriate extension of pi-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.