Visualized Solvent Polarity Sensor Based on Dual-Fluorescent Perovskite Quantum Dots–Ru(bpy) ₃ ²⁺ @SiO ₂ Nanocomposites for the Detection of Solvent Polarity

Determination of the solvent polarity is important across various scientific and industrial fields. Classic empirical parameters for evaluating solvent polarity, such as Rohrschneider–Snyder parameters (P′), Reichardt’s ET(30), Kamlet–Taft parameters, dielectric constant (ε) measurement, and Hansen solubility parameters (HSPs) often suffer from complicated instrumentation and measurement operation, which seriously limits their applications in real-time and fast determination and selection of unknown solvent polarity. In this work, we utilize recently emerging perovskite quantum dots (PQDs) with extremely high fluorescence quantum yield, high sensitivity to solvent polarity, and facile preparation and surface engineering to to develop a visualized and disposable solvent polarity sensor based on dual-fluorescent PQDs@SiO2/Ru(bpy)32+@SiO2 (PQDs@SiO2/Ru(II)@SiO2) nanocomposites. Among the nanocomposites, the components of PQDs@SiO2 are stable in nonpolar solvents but not stable in polar solvents due to degradation. Meanwhile, the component Ru(bpy)32+ is stable in both polar and nonpolar solvents, giving a constant red background fluorescence. Therefore, when inserting the glass slide loaded with PQDs@SiO2/Ru(II)@SiO2 nanocomposites into a nonpolar solvent, it retainss green light emission since the fluorescence quantum yield of PQDs is much larger than that of Ru(bpy)32+. In contrast, when the glass slide contacts with polar solvents, its fluorescence color will change from green to yellow, then orange, and finally to red due to the instability of PQDs in this case. The complete color change time from initial green to final red (tccc) was proposed as a new type of solvent polarity parameter. This work not only provides an empirical parameter for evaluating solvent polarity but also opens up an avenue for detecting solvent polarity using functional nanomaterial.