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A novel fluorescent material that can change its emission properties in response to different external stimuli holds significant importance for the development of sensors, information storage, and encryption materials. In this work, we designed and synthesized two zinc(II) coordination compounds, [Zn(HL)I2]·CH3OH (1) and [Zn(HL)Br2]·CH3OH (2), which exhibit remarkable changes in their emission properties under three different external stimuli. The two compounds were prepared using a simple one-pot method by reacting zinc(II) salts with 4-(N,N-diphenylamino)benzaldehyde and 3-amino-2-pyridinone. Under the stimulation of NH3 vapor, both compounds underwent decomposition, leading to a transformation of their fluorescence from yellow to blue, exhibiting a significant blue-shift of more than 170 nm. After exposure to HCl vapor, the fluorescence color of the two original compounds changed from yellow to red, and the color change could be easily distinguished by the naked eye under UV light irradiation. Then after fumigation with NH3 vapor, the color of both samples changed from red to blue. Based on the high-contrast NH3-responsive properties and HCl-responsive properties, we designed and developed test papers capable of detecting HCl vapor and NH3 vapor. Furthermore, due to the transformation from the crystalline state to the amorphous state during grinding, the two compounds also demonstrated high-contrast mechanochromic luminescence properties. After grinding, the color of the two compounds changes significantly from yellow to orange. [ABSTRACT FROM AUTHOR]

Two complexes based on phosphorescent viologen ligands have been synthesized. Complexes 1 and 2 not only possess reversible photochromic and electrochromic properties, but also exhibit fluorescence and persistent luminescence. They have potential applications in inkless print, color-changing films, data encryption, and anti-counterfeiting. [Display omitted] • Complexes 1 and 2 exhibit reversible photochromic and electrochromic behaviors. • Complexes 1 and 2 exhibit long-lived persistent phosphorescence. • Complexes show great potential in data encryption and anticounterfeiting. • Complexes have potential applications in inkless printing, color-changing films. Viologen-based complexes have garnered significant attention due to their multifunctional stimuli-responsive properties and tunable persistent luminescence. However, achieving ultralong afterglow emission and color change in these complexes remains a challenge, limiting their application in the field of persistent luminescence. Herein, two novel viologen-based complexes were successfully designed and synthesized using N,N′-bis(2-carboxyethyl)-4,4′-bipyridinium dichloride (H 2 bybpy) ligands and trimesic acid (H 3 BTC) with the transition metals Zn(II)/Cd(II). Complexes 1 and 2 display reversible photochromic and electrochromic properties. Interestingly, complexes 1 and 2 in their crystal state exhibit dual fluorescence and persistent luminescence, emitting a green and cyan afterglow when the UV lamp is turned off at 77 K. Incorporating phosphorescent molecules and changing the metal significantly extended the duration of persistent luminescence and altered the hue. The complexes were also demonstrated to have potential applications in inkless printing, color-changing films, data encryption, and anti-counterfeiting. This work enhances the application of viologen-based complexes in light-controlled persistent fluorescence and provides ideas for achieving ultra-long afterglow emission. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel "turn-on" fluorescent chemosensor for the detection of Al3+ was developed. • The probe exhibited anti-interference recognition and low detection limit of 22.0 nM. • The detection mechanism of the probe for Al3+ is the formation of Al-complex. • HL can be utilized as a film to detect Al3+ ions. Many Al3+ sensors have been reported in the literature, the lack of spectral features and poor coordination of Al3+ pose a significant challenge to detection. Herein, the design and synthesis of a Schiff's base (HL) sensor is reported, which exhibits a turn-on response to Al3+ in an aqueous solution, and the fluorescence color of HL from light green to cyan upon the addition of Al3+. The limit of detection (LOD) for Al3+ was determined to be 2.20 x 10−8 M. The mechanism for fluorescence sensing was revealed through the analysis of single-crystal X-ray diffraction, DFT, and UV–vis absorption spectra. HL gradually coordinated with Al3+ during the titration process, leading to the formation of HL-Al crystals. The outcome of this study resulted in the successful preparation and application of flexible and foldable films for visual detection of Al3+. [ABSTRACT FROM AUTHOR]