Microstructural Modulation of Isomorphic Luminescent Coordination Polymers To Achieve Sensing Effect Transformation

The sensing effect transformation is first exploited by microstructural modulation. Two AIE functional ligands L-1 and L-2 were developed to construct two isomorphic coordination polymers [Cu(L-1)₂(SCN)₂]_n (1) and [Cu(L-2)₂(SCN)₂]_n (2), respectively (L-1 = 4,4′-((9H-fluoren-9-ylidene)-methylene)dipyridine; L-2 = 5,5′-((9H-fluoren-9-ylidene)-methylene)dipyrimidine). 1 and 2 exhibit 1-D single-chain architectures and have good water, pH, and thermal stabilities. 1 and 2 show the functional-ligand-originated luminescence and reduced emission intensities. L-1 and L-2 stack in a back-to-back manner in 1 and 2 with the distances of 4.61 and 5.38 Å, resulting in distinct MnO₄^– sensing effects for 1 and 2. 1 exhibits “turn-off” (luminescence quenching) MnO₄^– sensing. In a sharp contrast, 2 shows “turn-on” (luminescence enhancing) MnO₄^– sensing ability with ultrahigh sensitivity. Particularly, 2 represents the first “turn-on” MnO₄^– sensor. Their sensing mechanism toward a distinct MnO₄^– sensing effect is discussed in detail.