Brightly Phosphorescent Trinuclear Copper(I) Complexes of Pyrazolates:  Substituent Effects on the Supramolecular Structure and Photophysics

Abstract

Synthetic details, solid-state structures, and photophysical properties of a group of trimeric copper(I) complexes containing pyrazolate ligands are described. The reaction of copper(I) oxide and the fluorinated pyrazoles [3-(CF(3))Pz]H, [3-(CF(3)),5-(Me)Pz]H, and [3-(CF(3)),5-(Ph)Pz]H leads to the corresponding trinuclear copper(I) pyrazolates, {[3-(CF(3))Pz]Cu}(3), {[3-(CF(3)),5-(Me)Pz]Cu}(3), and {[3-(CF(3)),5-(Ph)Pz]Cu}(3), respectively, in high yield. The {[3,5-(i-Pr)(2)Pz]Cu}(3) compound was obtained by a reaction between [Cu(CH(3)CN)(4)][BF(4)], [3,5-(i-Pr)(2)Pz]H, and NEt(3). These compounds as well as {[3,5-(Me)(2)Pz]Cu}(3) and {[3,5-(CF(3))(2)Pz]Cu}(3) adopt trimeric structures with nine-membered Cu(3)N(6) metallacycles. There are varying degrees and types of intertrimer Cu...Cu interactions. These contacts give rise to zigzag chains in the fluorinated complexes, {[3-(CF(3))Pz]Cu}(3), {[3-(CF(3)),5-(Me)Pz]Cu}(3), {[3-(CF(3)),5-(Ph)Pz]Cu}(3), and {[3,5-(CF(3))(2)Pz]Cu}(3), whereas the nonfluorinated complexes, {[3,5-(Me)(2)Pz]Cu}(3) and {[3,5-(i-Pr)(2)Pz]Cu}(3) form dimers of trimers. Out of all the compounds examined in this study, {[3-(CF(3)),5-(Ph)Pz]Cu}(3) has the longest (3.848 Angstroms) and {[3,5-(Me)(2)Pz]Cu}(3) has the shortest (2.946 Angstroms) next-neighbor intertrimer Cu...Cu distance. The Cu...Cu separations within the trimer units do not vary significantly (typically 3.20-3.26 Angstroms). All of these trinuclear copper(I) pyrazolates show bright luminescence upon exposure to UV radiation. The luminescence bands are hugely red-shifted from the corresponding lowest-energy excitations, rather broad, and unstructured even at low temperatures, suggesting metal-centered emissions owing to intertrimer Cu...Cu interactions that are strengthened in the phosphorescent state. The {[3-(CF(3)),5-(Ph)Pz]Cu}(3) compound exhibits an additional highly structured phosphorescence with a vibronic structure corresponding to the pyrazolyl (Pz) ring. The luminescence properties of solids and solutions of the trimeric compounds in this study show fascinating trends with dramatic sensitivities to temperature, solvent, concentration, and excitation wavelengths.

Supramolecular Phosphorescent Trinuclear Copper(I) Pyrazolate Complexes for Vapochromic Chemosensors of Ethanol

“…4a). Such luminescent profile gave a large Stokes shift (∆λ) in 279, 304, 290, 322 and 338 nm, indicating the characteristics of phosphorescent compounds [21,[23][24][25][26][27][28][29][30][31][32][33][34]. Moreover, the luminescent decay measurements in excitation and emission maxima as shown in Fig.…”

“…Moreover, by controlling the elongation of the assembly or shortening the distance of metalmetal interactions, the self-assembled structures can be tuned using intermolecular metallophilic interaction of the metal complexes [24]. Spectroscopically, the luminescence properties of complexes 2 A-E were performed using DR UV-Vis spectrometer and photoluminescent spectrofluorometer [25]. The absorption spectra were measured to find the maximum energy for excitation of electrons from ground to excited state in the emission measurement.…”

“…5b were evaluated to give phosphorescent lifetime (τ) = 7.440.7, 7.601.5, 7.370.4, 8.690.3 and 8.161.8 μs at room temperature for complexes 2 A-E , respectively. Hence, complexes 2 A-E were successfully confirmed as phosphorescent compounds by metal-centered triplet excited states of the weak Cu(I)-Cu(I) metallophilic interaction [19,[23][24][25][26][27]. Considering the advantages of copper(I) complexes in their phosphorescence properties, it can be developed as promising vapochromic chemosensors based on changes in optical properties upon exposure to VOCs [35].…”

“…6f, green dot). Such quenching of intensity in 100% indicates that the chairlike coordination geometry of Cu(I)-Cu(I) metallophilic interaction [4,[19][20][21][22][23][24][25][26][27]35] was totally disrupted through the columnar assembly of the weak intermolecular interaction. In this case, Cu(I) ions in one pyrazole ring are unable to form metal-metal interaction with other Cu(I) ions of the ligand.…”

Cupriphication of gold to sensitize d 10 –d 10 metal–metal bonds and near-unity phosphorescence quantum yields

“…Although the former compound was studied for decades (22,23), the crystal structure of [Au(μ-C 2 ,N 3 -BzIm)] 3 was only recently published; it exhibited a semiprismatic conformation with one long (3.558 Å) and two short (3.346 Å) intertrimer distances to manifest its strong aurophilic interactions (11). The copper precursor for 1-4 has been studied by Dias et al (24) 3 ] that nonetheless represented weaker aurophilic interaction vs. its hexagonal polymorph (27). Even with partial oxidation via organic electron acceptors, some of the aforementioned cyclotrimers exhibited shortened Au⋯Au intertrimer distances that nevertheless remained >3.15 Å (22, 23), which are still much longer than the two 2.8750(8) Å "intertrimer" Cu I -Au I bonds in 4a herein.…”