Donor-acceptor type porphyrin based covalent organic framework films as a photocathodic sensor for the polybrominated diphenyl ethers detection

The low signal intensity of photoactive materials limits the sensitivity of cathodic photoelectrochemical (PEC) sensors, yet controlling electron/media transport pathways can significantly improve performance and broaden their application potential. Herein, donor (D)-acceptor (A) type covalent organic frameworks (COFTAPP-Bpy) films was synthesized on the liquid/liquid interface via a bottom-up growth method, in which 5,10,15,20-tetrakis (4aminophenyl) porphyrin (TAPP) and 2,2 '-bipyridine-5,5 '-dicarbaldehyde (Bpy) were woven into the COFs skeleton. Specifically, the D-A type COFTAPP-Bpy formed independent electron-hole transport pathways by adjusting organic ligands in the framework, which extended the charge separation lifetime and enhanced photoelectric conversion efficiency. Moreover, the porous framework of COFTAPP-Bpy films offered distinct molecular pathways for dissolved oxygen to diffuse into the internal of the framework, increasing its utilization ratio. Through the synergistic effects of the above factors, the photoelectric current of the COFTAPP-Bpy films was enhanced 4.0 times compared to the porphyrin monomer. Meanwhile, molecularly imprinted polymers (MIPs) were modified on the COFTAPP-Bpy films photocathodes (MIP/COFTAPP-Bpy), enabling the selective recognition of decabromodiphenyl ether (BDE-209) molecules with excellent linearity over the range of 0.001-10 mu M and a detection limit as low as 0.3 nM. This work provided a straightforward approach for designing D-A COF films and presented a promising strategy to enhance charge and media transfer efficiency by modulating functional building blocks, thereby enabling the development of a high-performance PEC sensing platform.