Highly Ag+ Selective Tripodal Gold(I) Acetylide-based “Off–On” Luminescence Chemosensors based on 3(ππ*) Emission Switching

Newly prepared gold(I) acetylide-based luminescent cation sensors 1c and 1d, which bear a novel three–armed flexible conformation, together with control molecule 2c, were synthesized in four steps. 1c and 1d exhibit the π → π* absorption of the acetylide ligands in fluid solutions and produce the 3(ππ*) emission of the acetylide ligands in the solid state and degassed THF solution. The 3(ππ*) emission of 1c in DMSO can be turned on upon addition of Ag+. The binding ratio between 1c and Ag+ as well as the binding constant log K were determined as 1:1 and 4.35 ± 0.12 respectively by UV–vis titration experiments. The formation of [1c·Ag]+ adduct, which leads to the appearance of new up-field peaks, was confirmed by 1H NMR spectroscopic titrations. The control 1H NMR titration experiments for the acetylide-free analogue 1a and single-armed analogue 2c indicate the acetylide groups and tripodal structures are responsible for the binding of Ag+. The control experiment for tripodal gold(I) acetylide analogue 1d suggests the change of PPh3 with P(2-Py)Ph2 induces similar binding affinity toward Ag+ but less selectivity toward Ag+. Free 1c also exhibits the anion binding affinity toward F–, but the Ag+ adduct [1c·Ag]+ shows less affinity toward F–.