Temperature-dependent photoluminescence down to 77 K of organotin molecular rotors: eco-friendly synthesis, photophysical characterization, X-ray structures, and DFT studies

Fluorescent organotin compounds are useful in sensing, optoelectronic devices, and in vitro bioimaging. Although in vitro fluorescence bioimaging shows low resolution at room temperature, a better resolution is possible at cryotemperatures. Therefore, the search for new cryoluminescent materials with potential application in high-resolution fluorescence bioimaging remains a great challenge. Herein, we report the cryoluminescence properties of two fluorescent bis-organotin compounds, namely, BisNTHySnBu2 (5) and BisNTHySnPh2 (6), synthesized via microwave irradiation. All compounds were fully characterized using 1H, 13C, and 119Sn NMR spectroscopy, Raman spectroscopy, IR spectroscopy, and HR-MS. The 119Sn δ and 3J(1H,119Sn) of 5 and 6 indicate that two Sn-ligands are chemically and electronically equivalent, as confirmed by cyclic voltammetry. The crystal structure of 6 showed pentacoordinate tin atoms with skeleton ligands. The study of self-assembled monolayers of both Sn-complexes via STM microscopy revealed a similar supramolecular packing in lamella-like patterns, adopting a face-on arrangement, where molecules stay flat lying on HOPG in accordance with the height profile of closely packed monolayers on graphite of about 0.33 nm thickness. However, only the Sn complex 6, which bears phenyls, covers large surface areas. The photophysical properties of bis-organotin compounds were also investigated in solution (room and low temperatures) and in the solid state. Good luminescence properties in solutions with fluorescence quantum yields (Φ) of approximately 35% and 50% were found. Despite this, Φ is quenched in the solid state because of aggregation, as supported by solvent/non solvent fluorescence studies, which is in agreement with STM and AFM investigation.

Cyclic Trinuclear Copper(I) Complex Exhibiting Aggregation-Induced Emission: A Novel Fluorescent Probe for the Selective Detection of Gold(III) Ions

Coordination complexes with aggregation-induced-emission (AIE) behavior has drawn much attention because of their promising applications. Conventionally, the AIE-active metal-organic complexes are prepared from an AIE-active organic ligand, and the construction of such coordination complexes from aggregation-caused-quenching (ACQ) ligands is still challenging. Herein, we have synthesized two new cyclic trinuclear complexes (CTCs), namely, 1 and 2, from copper(I) and silver(I) and a ACQ ligand [4-(3,5-dimethyl-1H-pyrazol-4-yl)benzaldehyde, HL]. (1) exhibited AIE behavior, and the emission intensity is enhanced ∼20 times when it aggregates, which can be attributed to its tight packing and multiple intermolecular hydrogen bonds that restrained the intramolecular rotation, as confirmed by single-crystal X-ray diffraction analysis. On the other hand, (2) displayed ACQ effects, and the emission intensity is decreased ∼5 times when it aggregates. This ACQ behavior of 2 is related to its loose packing and free rotation of the ligand in crystals, resulting in nonradiative decay and fluorescence quenching. Interestingly, the CTCs 1 and 2 both exhibited a good affinity to gold(III) ions, allowing selective detection and sensing of gold ions. More importantly, the 2 shows a good limit of detection (3.28 μmol/L) and an ultrafast responsive time (∼2 s). Our studies pave a new route to designing novel AIE-active coordination complexes and further exploring the functionality of CTCs.

Luminescent polymorphic aggregates of trinuclear Cu(I)-pyrazolate tuned by intertrimeric CuNPy weak coordination bonds

Five luminescent polymorphic aggregates of trinuclear Cu(i)-pyrazolate, namely [anti-Cu3L3]2 (1), [syn-Cu3L3·C2H5OH]2 (2), [anti-Cu3L3·C2H5OH]n (3), [anti-Cu3L3·0.5C7H8]n (4) and [syn-Cu3L3·C8H10]n (5) (HL = 4-(pyridin-4-ylthio)-3,5-dimethyl-1H-pyrazole), were reported. The trimeric Cu3L3 fragments present syn- and anti-conformations dependent on the dangled direction of 4-pyridyl groups on the two sides of the Cu3Pz3 plane (Pz = pyrazolate). Intertrimeric NPyCu weak coordination bonds associate these Cu3L3 fragments together to form dimeric or polymeric structures, which are further stabilized by crystallized solvent molecules or intertrimeric CuCu interactions. The solvated complexes (3-5) may be transformed into the unsolvated complex 1 by evacuation of the crystallized solvents upon heating. All these complexes emit from green to yellow under UV irradiation, which originated from the triplet excited states of metal to ligand charge transfer (3MLCT) mixed with intertrimeric CuCu interactions. This work provides a novel kind of supramolecular aggregate based on Cu3Pz3 beyond the classical π-acidbase adducts and metallophilicity-dependent dimers/oligomers.

Sonochemical synthesis of a trinuclear Cu(ii) complex with open coordination sites for the differentiable optical detection of volatile amines

A discrete trinuclear Cu(ii) complex, namely, [Cu₃(pzdc)₂(dpyam)₂(H₂O)₄] (1) (H₃pzdc = pyrazole-3,5-dicarboxylic acid, dpyam = 2,2′-dipyridylamine) was simply synthesized by the sonochemical process and structurally characterized. The single-crystal X-ray diffraction analysis revealed that three adjacent Cu(ii) centers are linked via two bridging pzdc ligands to form a trinuclear Cu(ii) unit. Each trinuclear Cu(ii) unit contains open coordination sites with two trigonal bipyramidal Cu(ii) centers and one elongated octahedral geometry. Moreover, the open coordination site of 1 was occupied by a small molecule, leading to the guest-induced structural transformation with chromism that was verified by FT-IR, UV-vis diffuse reflectance spectra, elemental analysis, PXRD, and SEM techniques. Compound 1 exhibits color change along with structural transformation in methanol media and after the dehydration process. Also, 1 shows different color responses after exposure to different amine vapors. In addition, compound 1 was conveniently deposited onto a filter paper by a sonochemical method used as a portable test strip for the discriminative qualitative detection of amines.

A trinuclear Cu(ii) complex with open coordination sites for the differentiable optical detection of volatile amines.

Coinage-Metal-Based Cyclic Trinuclear Complexes with Metal-Metal Interactions: Theories to Experiments and Structures to Functions

Among the d¹⁰ coinage metal complexes, cyclic trinuclear complexes (CTCs) or trinuclear metallocycles with intratrimer metal-metal interactions are fascinating and important metal-organic or organometallic π-acids/bases. Each CTC of characteristic planar or near-planar trimetal nine-membered rings consists of Au(I)/Ag(I)/Cu(I) cations that linearly coordinate with N and/or C atoms in ditopic anionic bridging ligands. Since the first discovery of Au(I) CTC in the 1970s, research of CTCs has involved several fundamental areas, including noncovalent and metallophilic interaction, excimer/exciplex, acid-base chemistry, metalloaromaticity, supramolecular assemblies, and host/guest chemistry. These allow CTCs to be embraced in a wide range of innovative potential applications that include chemical sensing, semiconducting, gas and liquid adsorption/separation, catalysis, full-color display, and solid-state lighting. This review aims to provide a historic and comprehensive summary on CTCs and their extension to higher nuclearity complexes and coordination polymers from the perspectives of synthesis, structure, theoretical insight, and potential applications.

A systematic investigation of structural transformation in a copper pyrazolato system: a case study

Dissolution-recrystallization structural transformation (DRST) is a powerful tool to unravel unequivocally the mechanism of dynamic conversion processes, based on the structures of the initial reactants, final products and sometimes intermediates isolated from the reaction mixture. Herein, we illustrate the details of the conversion processes of (CuIpz)3 into [CuII(OH)pz]6 (pzH = 4-chloro-3,5-diphenylpyrazole) through DRSTs. Based on crystal structure determination and spectroscopic methods, the most encountered species, (CuIpz)3, is in equilibrium with (CuIpz)4 in solution with the tetramer becoming dominant at low temperature, indicating an entropy-controlled conversion between these two structural isomers. The CuI trimer/tetramer in solution further experiences an oxidation if exposed to the open air, resulting in the formation of a pentanuclear mixed-valence intermediate CuI3CuII2(OMe)2pz5 which can be isolated as single crystals at -20 °C and has been structurally characterized for the first time. The final product isolated from the solution is the fully oxidized hexanuclear [CuII(OMe)pz]6, which is easily transformed into [CuII(OH)pz]6 in the presence of humidity.

Thermo-responsive light-emitting metal complexes and related materials

This review discusses the fundamentals and design strategies for the development of thermo-responsive metal–ligand coordination materials and the applications of these materials in temperature sensing, bioimaging, information security, etc.

White Light from Blue Fluorescence and Sensitized Yellow Long-Afterglow Phosphorescence of o-Terphenyl in Its π-Acid···Base Adduct with Ag3Pz3

White-light emission with CIE (0.32, 0.34) was realized for an o-terphenyl (oTP) molecule in its Ag₃[3,5-(CF₃)₂Pz]₃ (Pz = pyrazolate) sandwiching adduct, originating from the hybrid of fluorescence and sensitized long-afterglow phosphorescence of oTP. Density functional theory (DFT) and time-dependent DFT calculations revealed that heavy-atom effects of Ag play a crucial role in sensitization of the triplet of oTP, giving off its ultralong phosphorescence.

The π-acidity/basicity of cyclic trinuclear units (CTUs): from a theoretical perspective to potential applications

Cyclic trinuclear units (CTUs) based on Au(i), Ag(i) and Cu(i) cations, featuring near planar nine-membered coordination rings, represent an important class of metal-organic π-acids/bases with highly adjustable π-acidity/basicity. Their superior π-acidity/basicity coupled with Lewis-acidic and metalmetal bonding sites offers excellent attraction for a wide range of acidic/basic species, and usually followed by noticeable changes of luminescence or charge transfer behaviors. A series of representative cases from the past two decades have been selected herein for such cyclic trinuclear units in both oligomeric and polymeric systems. Their fascinating and profound potential applications related to π-acidity/basicity are highlighted, including molecular absorption and separation, luminescence sensing and detection, organic light-emitting diodes (OLEDs), metal-organic field-effect transistors (MOFETs), molecular wires, and catalysis. The challenges in improving the performance for practical application will also be discussed.

Luminescent cyclic trinuclear coinage metal complexes with aggregation-induced emission (AIE) performance

A series of TPE-incorporated cyclic trinuclear coinage metal complexes have been prepared, and they show remarkable aggregation-induced emission performance.

Interaction of a trinuclear copper(i) pyrazolate with alkynes and carbon–carbon triple bond activation

The trinuclear copper(i) pyrazolate {[3,5-(CF₃)₂Pz]Cu}₃ forms η²-copper/alkyne triple bond coordinated structures in the presence of acetylenes.

A luminescent edge-interlocked prismatic heteroleptic metallocage assembled through a ligand replacement reaction

A luminescent edge-interlocked heteroleptic metallocages based on Cu₃(pyrazolate)₃ was prepared through a ligand replacement reaction from a homoleptic metallocage and a new ligand.

Photoluminescent Phosphinine Cu(I) Halide Complexes: Temperature Dependence of the Photophysical Properties and Applications as a Molecular Thermometer

Luminescent thermometers have attracted much attention, because of their fast response, high sensitivity, and noninvasive operation, relative to other traditional thermometers. The extensive studies on the temperature-dependent luminescent properties of Cu(I) complexes make this low-cost metal source a promising candidate as a component of thermometers. Herein, we prepared three luminescent phosphinine Cu(I) complexes whose emission lifetimes are precisely dependent on the temperature variations. For practical utilization, sensor films have been fabricated by doping these Cu(I) complexes into the matrices of polyacrylamide. These films not only exhibit excellent linear correlations between the temperature and emission lifetime over the wide range of 77-337 K, but also show high sensitivity (with the best one to -6.99 μs K^-1). These are essential factors for the application in luminescent molecular thermometers. Moreover, the emission mechanism for these Cu(I) complexes are rationalized by the combination of experimental and theoretical results.