Ultrastable two-dimensional fluorescent conjugated microporous polymers containing pyrene and fluorene units for metal ion sensing and energy storage

This study aims to synthesize three conjugated microporous polymers (CMPs) [Py-F CMP, TPE-F CMP, and TBN-F CMP] via the Suzuki coupling reaction of 9,9-dihexylfluorene-2,7-diboronic acid [F-B(OH)₂] with three brominated derivatives, pyrene (Py), tetraphenylethylene (TPE), and tetrabenzonaphthalene (TBN). The functional groups and chemical structures of the three synthesized CMPs were confirmed using FTIR and solid-state NMR analyses. Thermogravimetric analysis (TGA) revealed that TBN-F CMP has the most outstanding T_d10 = 418 °C and char yield = 63.3 wt% compared to the other two samples. The BET surface area and average pore size of TBN-F CMP were measured to be 200 m² g⁻¹ and ca. 1.8 nm, respectively. Furthermore, with excellent photoluminescence (PL) properties, all three new CMPs were well characterized using a spectrophotometer, and the fluorescence emission spectra were clearly drawn. As a result, we found that Py-F CMP can detect Pb²⁺ ions specifically and selectively compared to the other two CMPs. The sensitivity of Pb²⁺ was calculated and fitted with linear coefficients (R₂ = 0.9752) to determine the Pb²⁺ ion concentration over the ranges of 0.1–2.0 µM, and the detection limit was estimated to be 0.01 µM. Finally, with outstanding capacitance and stability of up to 195 F g⁻¹ and 90% over 2000 cycles, TBN-F-based CMP has been successfully applied to electrochemical measurements.