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