Engineering Coordination Frameworks by Cyclotriphosphazene-Functionalized Tectonics and a Terpyridine-Pincer Ligand for Efficient Photocatalytic Degradation of Organic Dyes

Engineering the Cd(II) coordination sphere with a terpyridine-pincer ligand and tuning the cyclotriphosphazene-fuctionalized multicarboxylates (H₄L1, H₄L2) produced one-dimensionally oriented self-assemblies, namely, [{Cd₂(trp)₂(L1)}]·DMF·3H₂O (PCP-1) and [{Cd₂(trp)₂(L2)}]·2DMF·H₂O (PCP-2). The solid-state structures of PCP-1 and PCP-2 were characterized by Fourier-transform infrared spectroscopy (FTIR), single-crystal and powder X-ray diffractions (SC and PXRD), thermal analyses (TGA), scanning electron microscopy-energy dispersive X-ray (SEM-EDX) analysis, and ultraviolet–visible diffuse reflectance measurements (UV-DRS) analysis. Both coordination polymers demonstrated efficient photocatalytic performance in the degradation of four organic dyes, namely, methylene blue (MB), methyl orange (MO), rhodamine B (RhB), and reactive orange 16 (RO16) under UVA light irradiation. Terpyridine aromatic rings exhibit strong π–π interactions (d(π···π) < 3.8 Å) that influence the formation of three-dimensional (3D) supramolecular network of PCP-1 and PCP-2 and thus can improve photocatalytic efficiency. Additionally, a plausible photocatalytic mechanism has been proposed through trapping experiments of active species to enhance our understanding of the photocatalytic degradation of dyes. Notably, the photocatalytic degradation activities of PCP-1 and PCP-2 are remarkably efficient in the degradation of MB with a rate of 96 and 91%, respectively, at 20 ppm dye concentration and 300 mg/L photocatalyst concentration. Also, PCP-1 and PCP-2 displayed high emission in the solid state. These findings contribute to understanding the potential of the cyclophosphazene-based coordination polymers in environmental remediation.