Temperature Tunable Optical Properties of Tetraheptylaluminum(III) Porphyrin Toward Molecular Thermometer

Amphiphilic aluminum(III) porphyrin (AlC7P) has been designed, and its aggregation-induced photophysics has been reported. The meso-positions of the aluminum(III) porphyrin are functionalized with a heptyl chain (C7), while the central porphyrin features an axial OH group on the Al center. The hydrophilic (OH) and hydrophobic (C7) properties combined with the Lewis acid (Al center) and Lewis base (OH group) functionality to facilitate the formation of aggregation through self-assembly. Spectroscopic studies indicate that aggregation can be modulated by solvent and temperature; it is more pronounced in long-chain hydrocarbon solvents, such as hexanes and n-heptane, and is favored at lower temperatures. At low temperature conditions, the aggregated molecules manifest low fluorescence yields, whereas at higher temperatures, the self-assembly breaks down to exhibit high fluorescence yields. This temperature-dependent aggregation-induced photophysical behavior observed in hexanes makes this porphyrin ideal for a luminescent molecular thermometer.