Green construction of porous organic polymers based on tris(β-keto-hydrazo)-cyclohexane used for the fluorescence detection of iodide ions and 2,4-dinitrophenol

The porous organic polymers based on tris(β-keto-hydrazo)-cyclohexane (the TKH-POPs) are new POPs, which are synthesized by the simple diazo-coupling isomerization reactions in aqueous solution at room temperature. The synthesis process is green, mild, and environment-friendly, which avoids the use of metal catalyst, high temperature, and toxic organic reagents. However, few studies have reported their use as fluorescent sensors up to now. Herein, two TKH-POPs (PDADM and PTDA) were synthesized with 4,4′-diaminodiphenylmethane, 4,4′-thiodianiline, and anhydrous phloroglucinol as the building blocks. The structures of PDADM and PTDA are the tris(β-keto-hydrazo)-cyclohexane forms rather than the azo tautomers. PDADM and PTDA are amorphous nanospheres with thermal stability up to 264 and 242 °C, and high BET surface areas of 1346 and 989 m² g⁻¹. PDADM and PTDA have high sensitivity and selectivity to iodide ion (I⁻) and 2,4-dinitrophenol (DNP). The K_SV values of PDADM and PTDA are 1.47 × 10⁴ and 2.41 × 10⁴ mol L⁻¹ for I⁻, and 1.89 × 10⁴ and 2.68 × 10⁴ L mol⁻¹ for DNP. The fluorescence sensing mechanisms of PDADM and PTDA to iodide ions include the heavy atom effect, inter filtration effect, and resonance energy transfer process, and that to DNP consist of resonance energy transfer process, photo-induced electron-transfer process, inter filtration effect, and hydrogen bonding interactions. This study lays a good foundation for the use of TKH-POPs as the fluorescent sensors to detect anions and nitro aromatic compounds.