Luminescent silver(I) complexes with pyrazole-tetraphenylethene ligands: turn-on fluorescence due to the coordination-driven rigidification and solvent-oriented structural transformation.

A new tetrapyrazole-modified tetraphenylethene (TPE) ligand L was designed and found to display “turn-on” fluorescence when it combines with Ag+ ions in dilute solution by restricting intramolecular rotation of TPE. A series of Ag complexes 1–7 were obtained, and they exhibit excellent fluorescence properties in the solid state. Compared with PF6−, the silver complex with the CF3SO3− anion can further enhance its fluorescence due to the transformation of its structure from Ag2L (2) to Ag4L2 (3). As zero-dimensional complexes, 1 and 3 have excellent piezochromic properties with a color change from blue to green. Furthermore, structural changes of 1 and 3 to the corresponding three-dimensional frameworks 4 and 5 occur upon immersing in ethanol. In addition, 1 can act as a potential fluorescent probe for sensing nitrile compounds.