Design, synthesis and functionalization of stimuli-responsive luminescent gold(i) alkynyl, chalcogenido and phosphinidene complexes

Abstract

A library of polynuclear gold(I) complexes with bridging alkynyl, chalcogenido and phosphinidene ligands has been synthesized and characterized. Their photophysical and stimuli-responsive properties have also been investigated.

A series of di- and tetranuclear alkynylcalix[4]arene-based gold(I) isocyanide complexes with different receptor sites for ion binding has been synthesized and characterized. Tetranuclear and dinuclear complexes with varying lengths of ethylene glycols, dinuclear gold(I) calix[4]crowns with varying crown sizes and dinuclear complexes with urea receptor sites were synthesized. Their electronic absorption and emission properties have been studied, with all the complexes showing emission in dichloromethane solution, in the solid state at 298 and 77 K and in the glass state at 77 K. One of the tetranuclear complexes was found to bind selectively to In3+ ions. Its binding affinity and selectivity have also been investigated and the binding constants and detection limits of the complex were also obtained. The signaling of the binding process was monitored by the formation of a new low-energy emission band, which was ascribed to the switching-on of intramolecular aurophilic interactions upon substrate binding. The solvent-induced self-assembly process and formation of nanoaggregates of the complexes with ethylene glycol pendants were also examined. Moreover, the anion-binding properties of the complexes with urea acceptor sites were also studied. Selective binding behavior towards H2PO4 ions was observed by electronic absorption and emission spectroscopy.

On the other hand, the design and synthesis of a series of hexanuclear [Au6(u-Ph2PNRPPh2)3(u3-E)2]2+ and decanuclear [Au10(u-Ph2PNRPPh2)4(u3-E)4]2+ (E = Se, S) chalcogenido gold(I) complexes with different bis(diphosphino)amine ligands were reported. The structures of the decanuclear complex, [Au10{u-Ph2PN(CH2-o-C5H4N)PPh2}4(u3-S)4](PF6)2, and hexanuclear complex, [Au6{u-Ph2PN(CH2-o-C5H4N)PPh2}3(u3-Se)2](PF6)2, were revealed by X-ray crystal analysis. The photophysical properties of the complexes were studied. The complex with pyridine pendant was found to crystallize into three different pseudo-polymorphs with different emission colors. The three forms were found to be interchangeable upon exposure to external stimuli such as mechanical grinding, temperature change and exposure to volatile organic compounds (VOCs). The acidochromic property of the complex was also studied. Moreover, the self-assembly properties of decanuclear gold(I) clusters with ethylene glycol pendants on the phosphine ligands have also been examined. Formation of spherical nanoaggregates and drastic luminescence enhancement were observed upon addition of water as a poor solvent into the methanol solutions of the complexes.

In addition, a series of hexanuclear phosphinidene gold(I) complexes, [Au6(-Ph2PNRPh2)3(u3-PR)2](PF6)2, has been synthesized and characterized. Phosphinidene ligands with substituent groups having different conjugation and chirality, combining with bis(diphosphino)amine ligands having different pendant groups, have been used in the preparation of the metal complexes. The complexes were found to be emissive in low-temperature methanol glass. The X-ray crystal structure of one of the complexes, [Au6(-Ph2PNPhPPh2)3(u3-PCy)2](PF6)2, was revealed to possess a distorted cubane structure. The solvent-dependent supramolecular assembly properties of the complexes have also been examined. Some of the complexes were found to form nanoaggregates upon addition of water into the DMSO solution. The transformation from irregular nanoaggregates to ring-like structures was observed upon increasing the water content. The thermodynamic parameters of the aggregation process have also been determined.