Hydrostatic Pressure-Induced Spectral Variation of Reichardt’s Dye: A Polarity/Pressure Dual Indicator

The famous solvatochromic Reichardt's dye was applied to quantify hydrostatic pressure in media. The UV/vis spectra of the dye in various organic solvents are shifted bathochromically or hypsochromically at the shorter- or longer-wavelength band, respectively, upon hydrostatic pressurization. The <i>E</i> _T value, determined by an absorption maximum, in ethyl acetate increases from 38.5 kcal mol^-1 at 0.1 MPa to 39.2 kcal mol^-1 at 300 MPa, which is mostly equal to the one in chloroform at 0.1 MPa. These spectroscopic origins were supported by the time-dependent density functional theory (TD-DFT) calculations. The concept and approach proposed in this paper, i.e., a dual indicator, should attract the attention of a broad spectrum in multidisciplinary science.