Design and synthesis of luminescence chemosensors based on alkynyl phosphine gold(i)-copper(i) aggregates

Abstract

Receptor-containing polynuclear mixed-metal complexes of gold(i)-copper(i) 1-3 based on a [{Au 3Cu 2(CCPh) 6}Au 3{PPh 2-C 6H 4-PPh 2} 3] 2+ (Au 6Cu 2) core with benzo-15-crown-5, oligoether and urea binding sites were designed and synthesized, respectively. These complexes exhibited remarkably strong red emission at ca. 619-630 nm in dichloromethane solution at room temperature upon photoexcitation at λ > 400 nm, with the emission quantum yield in the range 0.59-0.85. The cation-binding properties of 1 and 2 and the anion-binding properties of 3 were studied using UV-vis, emission and 1H NMR techniques. Complex 1, with six benzo-15-crown-5 pendants, was found to show a higher binding preference for K +, with a selectivity trend of K + ≫ Cs + > Na + > Li +. The addition of metal ions (Li +, Na +, K + and Cs +) to complex 1 led to a modest emission enhancement with a concomitant slight blue shift in energy and well-defined isoemissive points, which is attributed to the rigidity of the structure and the inhibited PET (photo-induced electron transfer) process from the oxygen to the aggregate as a result of the binding of the metal ion. The six urea receptor groups on complex 3 were found to form multiple hydrogen bonding interactions with anions, with the positive charge providing additional electrostatic interaction for anion-binding. The anion selectivity of 3 follows the trend F - > Cl - ≈ H 2PO 4 - > Br - and the highest affinity towards F - is attributed to the stronger basicity of F -, as well as its good size match with the cavity of the urea pocket. © 2011 The Royal Society of Chemistry.