Piezochromic Behavior of 2,4,6-Triphenylpyrylium Tetrachloroferrate

In advanced photonics, there is a growing interest in piezochromic luminescent materials that exhibit multicolor switching, driven by their potential applications in optical recording, memory, and sensors. Here, the piezochromic behavior of 2,4,6-triphenylpyrylium tetrachloroferrate (Py-FeCl₄) under high pressures from 0 to 9 GPa is reported. The observed multicolor changing properties of Py-FeCl₄ (yellow-orange-red-maroon-black) are found to be fully reversible upon decompression to ambient conditions. The mechanism of Py-FeCl₄ piezochromism is investigated via Raman, infrared, and UV-vis spectroscopy combined with powder X-ray Diffraction. The absence of structural phase transitions as well as the abrupt shifts of bandgap values together with characteristic Raman and IR peaks within 0-9 GPa suggests that the Py-FeCl₄ multicoloring switching behavior is driven by an electron transfer between the inorganic FeCl₄ ^- anion and the organic pyrylium cation. The obtained results demonstrate that Py-FeCl₄ dye is a good candidate for developing high-pressure sensing technologies designed to function in extreme environments. Moreover, due to the inherent role of molecular-structure relationships in the pyrylium salt's photophysical properties, findings suggest the potential discovery of piezochromic behavior in other pyrylium compounds.