Decisive Influence of the Metal in Multifunctional Gold, Silver, and Copper Metallacycles: High Quantum Yield Phosphorescence, Color Switching, and Liquid Crystalline Behavior

Abstract

Three cyclic trinuclear pyrazolate complexes with Au(I), Ag(I) or Cu(I) have been studied. These complexes have interesting and distinct optical and thermal properties depending on the metal, namely liquid crystalline behavior, red or deep-red phosphorescence at room temperature, thermoluminochromism and response to silver ions. The selected ligand, 4-hexyl-3,5-dimethylpyrazolate, maximizes the effect that the nature of the metals has on the properties of the complexes, thus allowing the intermolecular metallophilic interactions to be responsible for the optical properties. Moreover, the gold and silver complexes show columnar liquid crystal phases at high temperature. All of the complexes have good solubility properties for processing as poly(methyl methacrylate) (PMMA) doped films. Films of the gold, silver and copper complexes show interesting optical behavior such as wide-range color switching or phosphorescence turn-on upon cooling. In addition, films of the gold complex show a bright color switching (red to blue) in the presence of silver ions. The gold and copper complexes are bright phosphors with phosphorescent quantum yields of 90% in PMMA films, the highest values reported for this class of compounds at room temperature.

Observation of crystallisation dynamics by crystal-structure-sensitive room-temperature phosphorescence from Au(I) complexes

“…Some Au(I) complexes exhibit AIE activity owing to an intermolecular interaction known as the aurophilic interaction 25,26 , in which a non-covalent Au-Au bond is formed between molecules. Because of this interaction, the luminescence of Au(I) complexes can be increased by aggregation in condensed phases [27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46] . We hypothesised that the introduction of multiple aurophilic interactions could further enhance the AIE activity of Au complexes [36][37][38][39][40][41][42][43][44][45][46] and enable us to visualise a crystallisation process clearly.…”

A Computational Study of Metallacycles Formed by Pyrazolate Ligands and the Coinage Metals M = Cu(I), Ag(I) and Au(I): (pzM)n for n = 2, 3, 4, 5 and 6. Comparison with Structures Reported in the Cambridge Crystallographic Data Center (CCDC)

“…Lintang et al reported that trinuclear group 11 metal pyrazolate complexes are phosphorescent chemosensors for the detection of benzene [5] (for two recent papers on photoluminescence of the Dias and Fujisawa groups see [6,7]). The Serrano group published several papers that describe compounds related to those discussed in the present paper but with interesting mesogen properties when the pyrazolate ligands have long chains in positions three and five and the metal is Cu, Ag or Au [8][9][10][11]. Cano's group published similar results for complexes with gold(I) [12].…”

Systematic Study on Sensing Capability of Gold(I) Pyrazolate Complex for Vapochromic Chemosensors of Ethanol Vapors

“…Monitoring the excitation spectrum at 609 nm as the emission wavelength provides a peak at 278 nm, which is similar to its observed absorption spectrum. This result indicates a large Stokes shift from the difference of excitation and emission, originating from the excited triplet state of Au(I)-Au(I) bonding for phosphorescent metal complexes, which is also similar to the copper pyrazolate complex [12,15,31,32].…”