Temperature dependence of optical properties of aluminum(III) meso-tetra(benzo-15-crown-5)porphyrinate solution in toluene

Aluminum(III) meso-tetra(benzo-15-crown-5)porphyrinate (AlClTCP) is produced from aluminum(III) chloride and meso-tetra(benzo-15-crown-5)porphyrin (H₂TCP) in boiling pyridine. The structure of the novel compound was determined by electronic absorption spectroscopy, nuclear magnetic resonance, and MALDI TOF mass spectrometry. The color of the AlClTCP solution in toluene was found to depend on temperature, namely, the heated solution is pink, while the cooled one is green. Changes in the electronic absorption spectra and fluorescence spectra of the solution depending on temperature are analyzed. According to the data of dynamic light scattering, gradual cooling of the AlClTCP solution in toluene heated to 120°C results in the formation of nanoparticles with a mean diameter of several hundred nanometers that assume a spherical shape. The self-assembly is assumed to take place via the change from the monodentate coordination of the chloride anion by Al³⁺ cation in AlClTCP molecules to a bridgelike coordination.