A multifunctional luminogen: integrating AIE, persistent RTP, and stimuli-responsiveness for advanced information encryption, water quantification, and visualized acid vapor detection.

The development of multifunctional purely organic room-temperature phosphorescence materials remains a formidable challenge. Herein, a pyridine-bromobenzene-based luminogen named NNPA was successfully prepared, integrating both aggregation-induced emission (AIE) activity and pH-dependent fluorescence emission. More importantly, the fluorescence emission maxima of NNPA exhibits a monotonic red shift with increasing water content in THF-H2O mixtures, enabling precise water quantification over a broad range (0-90%). Remarkable acid-triggered fluorescence emission shifts are demonstrated, transitioning from 383 to 520 nm in solution and 390 to 465 nm in the crystalline state. Meanwhile, the ultralong phosphorescence lifetime undergoes a monotonic attenuation with increasing acid concentration, allowing for time-resolved, naked-eye sensing of acid vapors. Crucially, by incorporating Rhodamine B via melt-blending, a red-shifted room-temperature phosphorescence system reaching 655 nm was constructed through a Förster resonance energy transfer (FRET) mechanism, effectively overcoming the inherent wavelength barrier of organic afterglow. Leveraging alcohol solubility and processability of NNPA, eco-friendly flexible afterglow papers were fabricated, enabling advanced information encryption including static covert codes, dynamic time-resolved decryption, and 3D stereoscopic anti-counterfeiting. This work not only elucidates the intrinsic mechanism of multifunctional NNPA but also paves the way for next-generation smart photonic materials.