Detection of magnesium ion has been of great significance considering its critical physiological activities. Herein, we report ratiometric fluorescence detection of Mg2+ with high sensitivity and selectivity based on triplet–triplet annihilation (TTA) upconversion for the first time. Crown-ether functionalized anthracene derivatives were synthesized, which bifunctionally acted as not only annihilators to construct TTA upconversion systems but also the recognition probes for Mg2+ based on the photoinduced electron transfer (PET) mechanism. Their photophysical properties with the absence and presence of Mg2+ were comprehensively studied. It was found that solvents strongly influenced the photophysical properties and Mg2+-responsiveness. TTA upconversion systems with PtOEP as the sensitizer were further established and investigated. It turned out PtOEP/9-AEC in DCM exhibited an excellent linear relationship (R 2 = 0.9979) between the intensity ratio (the integrated upconverted luminescence intensity (I UC) over the integrated downshifted phosphorescence intensity (I PL), I UC/I PL) and the concentration of Mg2+ under the excitation of 532 nm with a limit of detection value of 2.52 μM and a high selectivity to Mg2+. This work opened a new perspective of designs and applications of TTA-upconversion-based ratiometric fluorescence for ion detection.

In this work, we provide a fabrication method for dual-responsive electrochromic (EC) polymer dispersed liquid crystal (PDLC) devices. The EC PDLC device was developed by combing the PDLC technique and a colored complex formed via a redox reaction without a specific EC molecule in a simple preparation method. The mesogen played dual roles in the device for scattering in the form of microdroplets and participating in the redox reactions. Orthogonal experiments were performed with the acrylate monomer concentration, the ionic salt concentration, and the cell thickness as factors to investigate the electro-optical performance for the achievement of optimized fabrication conditions. The optimized device presented four switchable states modulated by external electric fields. The light transmittance of the device was changed by an alternative current (AC) electric field while the color change was realized by a direct current (DC) electric field. Variations of mesogen and ionic salt species can modulate the color and hue of devices, which solves the disadvantage of a single color for traditional EC devices. This work lays the foundation for realizing patterned multi-colored patterned displays and anti-counterfeiting via screen printing and inkjet printing techniques.