Multistimuli-responsive tetraphenylethene molecular switches displaying acid-sensing, photochromism, and metal ion detection properties.

Aggregation-induced emission (AIE) smart materials with multiple stimulus responses have a wide range of applications. Here, a series of tetraphenylethylene (TPE) derivatives, TPEN 1 S 3 , TPEN 2 S 2 , TPEN 3 S 1 were synthesized. The sensitivity of molecules to pH, UV light, and metal ions could be effectively tuned by modulating the ratio of amino to sulfonic acid groups. These TPE derivatives exhibited yellow emissions in aggregated state due to the AIE characteristics. Acidification conversion of the NH 2 groups to NH 3 + for three molecules induced the suppression of intramolecular charge transfer (ICT), which resulted in a 72–102 nm blue shift in the fluorescence emission. Solid powders of these compounds exhibited reversible protonation-deprotonation process induced by HCl/NH 3 ·H 2 O vapor. TPEN 1 S 3 , TPEN 2 S 2 and TPEN 3 S 1 in solution could be photoactivated and emit blue fluorescence (ca. 482 nm, 475 nm, and 480 nm). Photocyclo-dehydrogenation reactions of compounds were triggered by the UV irradiation and the maximum cyclization ratios could reach 12%, 66%, and 50%, respectively. Protonation of NH 2 group significantly enhanced the rate of the photocyclo-dehydrogenation reaction. Furthermore, the solid powders of protonated compounds displayed pronounced reversible photochromic properties due to the generation of cyclization intermediate. In addition, TPEN 1 S 3 , TPEN 2 S 2 , and TPEN 3 S 1 exhibited responsiveness to a diverse range of metal ions. Specifically, the TPEN 2 S 2 molecule functioned as a photo sensor for Li + ions with a blue shift in fluorescence emission. The limit of detection (LOD) value was 0.679 μM. These multiple stimuli-responsive AIE molecules hold significant potential for use in advanced photo-controlled patterning, encryption applications, and the detection of metal ions. [Display omitted] • Novel AIE compounds TPEN 1 S 3 , TPEN 2 S 2 , TPEN 3 S 1 based on tetraphenylethylene (TPE) for photoluminescence (PL) sensors are fabricated. • Multi-stimuli responsive fluorescence of AIE compounds are investigated under acid, UV light and metal ions. • Amino group protonation can induce reversible fluorescence conversion and accelerate photocyclo-dehydrogenation reactions. • Probe TPEN 2 S 2 is good selectivity and sensitivity for Li + detection. • Three paper-based application scenarios are designed for information encryption and anti-counterfeiting. [ABSTRACT FROM AUTHOR]