Aggregation-Induced Emission-Active 1,4-Dihydropyridine-Based Dual-Phase Fluorescent Sensor with Multiple Functions

A N-2-phenylethyl-substituted 1,4-dihydropyridine derivative (NDHP) containing 5,5-dimethylcyclohexane-1,3-dione and naphthylethylene was designed and synthesized. NDHP acts as a multifunctional fluorescent sensor in dual phases. The crystal structure analysis confirms that the NDHP molecules have highly twisted conformations. The twisted conformation results in aggregation-induced emission properties and solid-state emission, by restricting the intramolecular free rotation in the aggregated or solid state. In the solid state, NDHP exhibits reversible mechanochromic properties as a result of the transition between the amorphous and crystalline states. NDHP also exhibits a rare phenomenon of acid-fumed solid-state emission enhancement owing to the change in packing mode from a zigzag arrangement to J-aggregation. The solid-state stimuli-responsive fluorescence switching is applied to realize a rewritable optical recording media and a multiple output combinational logic system. In solution, NDHP shows a selective fluorescence response for environmentally harmful Hg²⁺ , with a limit of detection of 2.7 nm. This results from the "turn-on" responsive behavior owing to the Hg²⁺ -triggered aggregation of the NDHP molecules. NDHP is also used in the imaging of intracellular Hg²⁺ in HeLa cells. These findings provide a feasible and attractive route for developing multifunctional fluorescent sensors for use in dual phases.