Pyrimidine based β-ketoenamine linked porous organic polymer as an on–off–on fluorescent sensing platform for the sequential detection of copper and phosphate ions

Abstract

The quest for intelligent and reversible fluorescence-based sensors has unlocked new frontiers in environmental and biological monitoring. Herein, we introduce DHBTC–TAP, a β-ketoenamine-linked porous organic polymer, meticulously designed for the sequential detection of copper (Cu²⁺) and phosphate (PO₄³⁻) ions with unparalleled precision and efficiency. The polymer is crafted via the solvothermal condensation of 2,4-dihydroxybenzenetricarbaldehyde and 2,4,6-triaminopyrimidine. This cutting-edge sensor exhibits strong fluorescence, which is dramatically quenched (“turn-off”) upon Cu²⁺ coordination due to the formation of a non-emissive ground-state complex. Remarkably, its fluorescence is restored (“turn-on”) upon phosphate introduction, establishing an exceptionally sensitive and reversible on–off–on sensing mechanism. This sensor has been successfully utilized in diverse applications, including the fabrication of sensor-coated paper strips, enabling real-time and visual detection of copper and phosphate ions. The DHBTC–TAP-coated strips serve as a portable, cost-effective, and highly efficient sensing platform, offering a convenient and rapid detection method for both biological and environmental monitoring. Their ability to provide instant fluorescence-based feedback makes them an excellent candidate for on-site analysis and field applications. Beyond its superior sensing capabilities, DHBTC–TAP transcends conventional detection, doubling as an intelligent INHIBIT logic gate, where Cu²⁺ and PO₄³⁻ serve as molecular inputs and fluorescence acts as the output. This smart logic behaviour enhances its potential for molecular computing, bioelectronics, and advanced sensing applications. With its seamless reversibility, higher surface area, rapid response, and dual functionality, DHBTC–TAP stands as a trailblazing platform for real-time monitoring, logic-based operations, and next-generation environmental and biomedical technologies.