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 Id, which bear a novel three armed flexible conformation, together with control molecule 2c, were synthesized in four steps. 1c and id exhibit the pi -> pi* absorption of the acetylicle ligands in fluid solutions and produce the 3(pi pi*) emission of the acetylide ligands in the solid state and degassed THF solution. The 3(pi pi*) 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 11 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 NMR spectroscopic titrations. The control H-1 NMR titration experiments for the acetylide-free analogue la 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 id suggests the change of PPh3 with P(2-Py)Ph-2 induces similar binding affinity toward As 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-.