Synthesis of Ag^I and Au^I Complexes from Tetra(thiophene‐NHC)‐Substituted Ethylene and Their Tunable Fluorescence Properties

Abstract

initiation of fluorescence has also been achieved by encapsulation in metalorganic frameworks. [21] Alternatively, TPE can be substituted in the para-position of the phenyl groups with selected donors which upon coordination to transition metals also lead to rigidification of TPE and initiates fluorescence behavior. [22][23][24][25][26] Recently, an NHC-substituted TPE has been prepared which upon coordination of two M I ions (M = Ag, Au) yields via rigidification an excellent fluorescence emitter in diluted solution (Scheme 1, left). [27] Subsequently various derivatives of NHC-substituted TPE derivatives and their metal complexes have been prepared showing that subtle changes in the structure of the NHC ligand lead to various organometallic architectures with varying photophysical properties. [28][29][30] The heteroaromatic thiophene contains more π-electrons than benzene [31,32] and the tetrathiophenesubstituted ethylene 1,2,3,4-tetrathienylethylene (TTE) has been shown to be a promising AIE emitter in the solid state based on restricted intramolecular rotation (RIM). [31] However, attempts to rigidify the TTE core through complex formation in order to possibly observe fluorescence in solution have not been reported.We have decorated the TTE molecule with four azolium units (imidazolium and benzimidazolium) and prepared the tetrakisazolium salts H 4 -L1(PF 6 ) 4 and H 4 -L2(PF 6 ) 4 (Scheme 1, right). In addition, 2,2′-(2,2-diphenylethene-1,1-diyl)dithiophene (DPDT) was functionalized at the thiophene units with imidazolium units to give the bisimidazolium salt H 2 -L3(PF 6 ) 4 (Scheme 2). The tetrakis-and bisimidazolium salts were subsequently used for the synthesis of a series of dinuclear NHC complexes of composition [M 2 L](PF 6 ) 2 (M = Ag, Au; L = L1, L2) and [M 2 (L3) 2 ](PF 6 ) 2 (M = Ag, Au, Scheme 2). The metal-NHC complexes exhibit the AIE phenomenon and temperaturedependent fluorescence emissions. Molecular structure analyses of the dinuclear tetracarbene complexes indicated that intra-and intermolecular S•••S interactions contributed to the observed red-shift of the emission in the aggregated state. Results and DiscussionThe tetra-NHC precursors H 4 -L(PF 6 ) 4 (L = L1, L2) were prepared following standard procedures. [27,28] The synthesis started Dinuclear silver(I) and gold(I) complexes have been prepared from (NHCthiophene)-substituted ethylene (NHC = N-heterocyclic carbene). Both the 1,2,3,4-tetrathienylethene (TTE)-bridged tetrakisazolium salts (H 4 -L1(PF 6 ) 4 and H 4 -L2(PF 6 ) 4 ) and the 2,2′-(diphenylethene-1,1-diyl)dithiophene (DPDT)bridged bisimidazolium ligand precursors H 4 -L3(PF 6 ) 2 have been prepared and are treated with Ag 2 O to give dinuclear tetracarbene complexes [Ag 2 L] (PF 6 ) 2 (L = L1, L2) and [Ag 2 (L3) 2 ](PF 6 ) 2 , respectively. The silver(I) complexes undergo a transmetalation reaction with [AuCl(THT)] (THT = tetrahydrothiophene) to furnish gold(I) NHC complexes with retention of the original structures. All complexes have been characterized by multi-nuclear magn...

Metal-N-Heterocyclic Carbene Chemistry Directed toward Metallosupramolecular Synthesis and Beyond

“…Typical AIE phenomena have also been observed in the other TPE-, TTE-, and DPDT-based poly-NHC assemblies mentioned above. 2,24,26,27,50 To explore more possibilities of poly-NHC metallosupramolecular assemblies, TPE-cored tetranuclear octa-mesoionic carbene (MIC) metallacages [M 4 (A47) 2 ](OTf) 4 (M = Ag I , Au I ) were prepared from a tetradentate MIC-TPE ligand featuring four 1,2,3-triazolium moieties (Figure 17a). 53 Resulting from the rigidification of MIC-TPE ligands upon the formation of M−C MIC bonds, [M 4 (A47) 2 ](OTf) 4 (M = Ag I , Au I ) fluoresced in dilute solutions and exhibited tunable fluorescence behaviors in different solvents and temperatures.…”

“…In an extension of emissive assemblies, 1,2,3,4-tetrathienyl­ethylene (TTE)-cored tetrakis-imidazolium salt H 4 - A19 (PF 6 ) 4 and 2,2′-(2,2-diphenylethene-1,1-diyl)­dithiophene (DPDT)-cored bis-imidazolium salt H 2 - A20 (PF 6 ) 2 were deployed (Figure ). Upon metalation, complex [Ag 2 A19 ]­(PF 6 ) 2 was obtained in 86% yield from H 4 - A19 (PF 6 ) 4 , and the complex of composition [Ag 2 ( A20 ) 2 ]­(PF 6 ) 2 was obtained in 83% yield from H 2 - A20 (PF 6 ) 2 , as confirmed by X-ray diffraction analyses.…”

“…Synthesis of TTE- and DPDT-cored assemblies (only the first atom of each N -substituent is depicted). Reproduced with permission from ref . Copyright 2022 Wiley-VCH.…”

“…As the water content increased, tunable fluorescence wavelengths and intensities were observed because of the inhibited movement of the TPE units owing to molecular aggregation. Typical AIE phenomena have also been observed in the other TPE-, TTE-, and DPDT-based poly-NHC assemblies mentioned above. ,,,, …”

Tetraphenylethene-based macrocycles with dual-ring topology: synthesis, structures, and applications

“…Han and Hahn et al synthesized the precursor 64 of the two-bridged bis-(imidazolium) ligand using 1,2,3,4-tetrathienylethylene-bridged tetrazolium salt 65 , followed by treatment with Ag 2 O to obtain dinuclear tetracarbene complex 66 (Scheme 9c). 73 In this reaction, the silver( i ) complex and [AuCl(THT)] (THT = tetrahydrothiophene) undergo a metal transfer reaction to generate the gold( i ) NHC complex, retaining the original structure. These complexes are characterized by multi-nuclear magnetic resonance (NMR), high-resolution electrospray ionization (HR-ESI) mass spectrometry, and single-crystal X-ray diffraction.…”