New Water Soluble and Luminescent Platinum(II) Compounds, Vapochromic Behavior of [K(H2O)][Pt(bzq)(CN)2], New Examples of the Influence of the Counterion on the Photophysical Properties of d8 Square-Planar Complexes

Vapor-Induced Assembly of a Platinum(II) Complex Loaded on Layered Double Hydroxide Nanoparticles

Controlled self-assembly of PtII complexes is key to the development of optical and stimuli-responsive materials, but designing and precisely controlling them is still difficult owing to weak intermolecular interactions. Herein, we report the successful water-vapor-induced assembly of an anionic PtII complex [Pt(CN)2 (ppy)]- (Hppy=2-phenylpyridine) electrostatically loaded onto cationically charged layered double hydroxide (LDH) nanoparticles consisting of Mg2+ and Al3+ ions. When the PtII complexes were densely loaded onto the LDH nanoparticles, the assembly was maintained, even in dilute aqueous media. In the case of sparse loading, the PtII complexes were loaded discretely in the dry state; however, when water vapor was adsorbed, the increased mobility of the PtII complexes led to their assembly on the LDH nanoparticles. The presence of water vapor led to a drastic change in luminescence from green to orange.

Structural modifications to platinum(II) pincer complexes resulting in changes in their vapochromic and solvatochromic properties

There is a need to develop rapidly responsive chemical sensors for the detection of low concentrations of volatile organic solvents (VOCs). Platinum pincer complexes have shown promise as sensors because of their colours and vapochromic and solvatochromic properties, that may be related to the non-covalent interactions between the pincer complexes and the guest VOCs. Here we report an investigation into a series of Pt(II) complexes based on the 1,3-di(pyridine)benzene tridentate (N⁁C⁁N) skeleton with the formula [Pt(N⁁C(R)⁁N)(CN)] (R = C(O)Me 2, C(O)OEt 3, C(O)OPh 4) with the fourth coordination site occupied by a cyanide ligand. Solid-state samples of the complexes have been tested with a range of volatiles including methanol, ethanol, acetone, dichloromethane and water, and while 2 displays thermochromism, 3 and 4 display rapidly reversible vapochromism and solvatochromism. These results are correlated with X-ray powder and single crystal X-ray structural data including an assessment of the crystal packing and the void space in the crystalline space. The cyanide ligand and the R substituents are involved in hydrogen bonding that creates the voids within the structures and interact with the solvent molecules that influence the Pt⋯Pt separation in the crystalline state.

Luminescent Anionic Cyclometalated Organoplatinum (II) Complexes with Terminal and Bridging Cyanide Ligand: Structural and Photophysical Properties

We present the synthesis and characterization of two series of mononuclear heteroleptic anionic cycloplatinated(II) complexes featuring terminal cyanide ligand Q⁺[Pt(C^N)(p-MeC₆H₄)(CN)]^- [C^N = benzoquinolate (bzq), Q⁺ = K⁺ 1 and NBu₄⁺ 4; 2-phenylpyridinate (ppy), Q⁺ = K⁺ 2 and NBu₄⁺ 5 and 2-(2,4- difluorophenyl)pyridinate (dfppy), Q⁺ = K⁺ 3 and NBu₄⁺ 6] and a series of symmetrical binuclear complexes (NBu₄)[Pt₂(C^N)₂(p-MeC₆H₄)₂(μ-CN)] (C^N = bzq 7, ppy 8, dfppy 9). Compounds 5, 6, and 7-9 were further determined by single-crystal X-ray diffraction. There are no apparent intermolecular Pt···Pt interactions owing to the presence of bulky NBu₄⁺ counterion. Slow crystallization of K[Pt(ppy)(p-MeC₆H₄)(CN)] 2 in acetone/hexane evolves with formation of yellow crystals, which were identified by single-crystal X-ray diffraction methods as the salt complex {[Pt(ppy)(p-MeC₆H₄)(CN)]₂K₃(OCMe₂)₄(μ-OCMe₂)₂}[Pt(ppy)(p-MeC₆H₄)(μ-CN)Pt(ppy)(p-MeC₆H₄)]·2acetone (10), featuring the binuclear anionic unit 8^- neutralized by an hybrid inorganic-organometallic coordination polymer {[Pt(ppy)(p-MeC₆H₄)(CN)]₂K₃(OCMe₂)₄(μ-OCMe₂)₂}⁺. The photophysical properties of all compounds were recorded in powder, polystyrene film, and solution states with a quantum yield up to 21% for 9 in the solid state. All complexes displayed bright emission in rigid media, and for the interpretation of their absorption and emission properties, density functional theory (DFT) and time-dependent DFT calculations were applied.

Multistimuli-Responsive Properties of Aggregated Isocyanide Cycloplatinated(II) Complexes

Here, we describe the neutral cyclometalated tert-butylisocyanide Pt^II complexes, [Pt(C^∧N)Cl(CNBu^t)] 1, the double salts [Pt(C^∧N)(CNBu^t)₂][Pt(C^∧N)Cl₂] 2, and the cationic complexes [Pt(C^∧N)(CNBu^t)₂]ClO₄ 3 [C∧N = difluorophenylpyridine (dfppy, a), 4-(2-pyridyl)benzaldehyde (ppy-CHO, b)]. A comparative study of the pseudopolymorphs 1a, 1a·CHCl₃, 1b, 1b·0.5Toluene, 1b·0.5PhF, and 3a·0.25CH₂Cl₂ reveals strong aggregation through Pt···Pt and/or π···π stacking interactions to give a variety of distinctive one-dimensional (1D) infinite chains, which modulate the photoluminescent properties. This intermolecular long-range aggregate formation is the main origin of the photoluminescent behavior of 1a and 1b complexes, which exhibit highly sensitive and reversible responses to multiple external stimuli including different volatile organic compounds (VOCs), solvents, temperatures, and pressures, with distinct color and phosphorescent color switching from green to red. Furthermore, complex 1b undergoes supramolecular self-assembly via Pt···Pt and/or π···π interactions into a polymer thin polystyrene (PS) film 10 wt % in response to toluene vapors, and 3a exhibits vapochromic and vapoluminescent behavior. Theoretical simulations on the dimer, trimer, and tetramer models of 1a and 1b have been carried out to get insight into the photophysical properties in the aggregated solid state.

Coordination-based vapochromic behavior of a luminescent Pt(ii) complex with potassium ions

Vapochromic Pt(ii) complexes that exhibit color and luminescence changes induced by the presence of vapor molecules have drawn considerable attention because of their potential use as vapor sensors. Generally, the vapochromic responsiveness of Pt(ii)-based complexes is difficult to envisage, because a typical molecular design facilitates the stabilization of a vapor-adsorbed form through weak intermolecular interactions. Herein, we investigate the vapochromic behavior of a Pt(ii) complex with potassium ions, which act as vapor coordination sites, by strongly stabilizing the vapor-adsorbed form. Upon exposure to N,N-dimethylacetamide and N,N-dimethylformamide vapors, the complex exhibits crystal structural transformation with luminescence spectral changes. Crystal structural analysis indicates that the vapor molecules are coordinated to the potassium ions after vapor exposure. This study suggests the possibility of inducing Pt(ii)-based vapochromic responsiveness through establishing potassium-ion-based vapor coordination sites.

A luminescent Pt(ii) complex with potassium ions was successfully synthesized and its coordination-based vapochromic behavior was investigated.

Chameleonic Photo- and Mechanoluminescence in Pyrazolate-Bridged NHC Cyclometalated Platinum Complexes

DFT investigations on the ground (GS) and the first triplet (T₁) excited state potential energy surfaces (PES) were performed on a new series of platinum-butterfly complexes, [{Pt(C^∧C*)(μ-Rpz)}₂] (Rpz: pz, 1; 4-Mepz, 2; 3,5-dmpz, 3; 3,5-dppz, 4), containing a cyclometalated NHC in their wings. The geometries of two close-lying local minima corresponding to butterfly spread conformers, 1s-4s, and butterfly folded ones, 1f-4f, with long and short Pt-Pt separations, respectively, were optimized in the GS and T₁ PES. A comparison of the GS and T₁ energy profiles revealed that an opposite trend is obtained in the relative stability of folded and spread conformers, the latter being more stabilized in their GS. Small ΔG (s/f) along with small-energy barriers in the GS support the coexistence of both kinds of conformers, which influence the photo- and mechanoluminescence of these complexes. In 5 wt % doped PMMA films in the air, these complexes exhibit intense sky-blue emissions (PLQY: 72.0-85.9%) upon excitation at λ ≤ 380 nm arising from ³IL/MLCT excited states, corresponding to the predominant 1s-4s conformers. Upon excitation at longer wavelengths (up to 450 nm), the minor 1f-4f conformers afford a blue emission as well, with PLQY still significant (40%-60%). In the solid state, the as-prepared powder of 4 exhibits a greenish-blue emission with QY ∼ 29%, mainly due to ³IL/³MLCT excited states of butterfly spread molecules, 4s. Mechanical grinding resulted in an enhanced and yellowish-green emission (QY ∼ 51%) due to the ³MMLCT excited states of butterfly folded molecules, 4f, in such a way that the mechanoluminescence has been associated with an intramolecular structural change induced by mechanical grinding.

Structural Insights into the Vapochromic Behavior of Pt- and Pd-Based Compounds

Anionic complexes having vapochromic behavior are investigated: [K(H₂O)][M(ppy)(CN)₂], [K(H₂O)][M(bzq)(CN)₂], and [Li(H₂O)_n][Pt(bzq)(CN)₂], where ppy = 2-phenylpyridinate, bzq = 7,8-benzoquinolate, and M = Pt(II) or Pd(II). These hydrated potassium/lithium salts exhibit a change in color upon being heated to 380 K, and they transform back into the original color upon absorption of water molecules from the environment. The challenging characterization of their structure in the vapochromic transition has been carried out by combining several experimental techniques, despite the availability of partially ordered and/or impure crystalline material. Room-temperature single-crystal and powder X-ray diffraction investigation revealed that [K(H₂O)][Pt(ppy)(CN)₂] crystallizes in the Pbca space group and is isostructural to [K(H₂O)][Pd(ppy)(CN)₂]. Variable-temperature powder X-ray diffraction allowed the color transition to be related to changes in the diffraction pattern and the decrease in sample crystallinity. Water loss, monitored by thermogravimetric analysis, occurs in two stages, well separated for potassium Pt compounds and strongly overlapped for potassium Pd compounds. The local structure of potassium compounds was monitored by in situ pair distribution function (PDF) measurements, which highlighted changes in the intermolecular distances due to a rearrangement of the crystal packing upon vapochromic transition. A reaction coordinate describing the structural changes was extracted for each compound by multivariate analysis applied to PDF data. It contributed to the study of the kinetics of the structural changes related to the vapochromic transition, revealing its dependence on the transition metal ion. Instead, the ligand influences the critical temperature, higher for ppy than for bzq, and the inclination of the molecular planes with respect to the unit cell planes, higher for bzq than for ppy. The first stage of water loss triggers a unit cell contraction, determined by the increase in the b axis length and the decrease in the a (for ppy) or c (for bzq) axis lengths. Consequent interplane distance variations and in-plane roto-translations weaken the π-stacking of the room-temperature structure and modify the distances and angles of Pt(II)/Pd(II) chains. The curve describing the intermolecular Pt(II)/Pd(II) distances as a function of temperature, validated by X-ray absorption spectroscopy, was found to reproduce the coordinate reaction determined by the model-free analysis.

Unique vapochromism of a paddlewheel-type dirhodium complex accompanied by dynamic structural and phase transitions

The one-dimensional coordination polymer [Rh2(HA)4]n (1G; HA = hexanoate) exhibits a drastic vapochromic color change from green to red upon exposure to pyridine (py) vapor. Heating the red discrete complex [Rh2(HA)4(py)2] (1R) at 338 K affords the purple discrete tetrarhodium complex [Rh2(HA)4(py)]2 (1P), which is an intermediate species in the vapochromic transformation of 1G to 1R. The obtained complexes 1G, 1R, and 1P differ not only in their color in the solid state, but also in their temperature-dependent phase transition properties.

Soft salts based on platinum(II) complexes with high emission quantum efficiencies in the near infrared region for in vivo imaging

Two soft salts (S1 and S2) based on platinum(ii) complexes with a near-infrared emission have been designed and synthesized. It has been demonstrated that S2 has a high photostability and a low cytotoxicity, and it has been successfully applied to in vivo imaging for the first time.

Bright Luminescent Platinum(II)-Biaryl Emitters Synthesized Without Air-Sensitive Reagents

Transition-metal complexes bearing biaryl-2,2'-diyl ligands tend to show intense luminescence. However, difficulties in synthesis have prevented their further functionalization and practical applications. Herein, a series of platinum(II) complexes bearing biaryl-2,2'-diyl ligands, which have never been prepared in air, were synthesized through transmetalation and successive cyclometalation of biarylboronic acids. This approach does not require any air- or moisture-sensitive reagents and features a simple synthesis even in air. The resulting (Et₄ N)₂ [Pt(m,n-F₂ bph)(CN)₂ ] (m,n-F₂ bph=m,n-difluorobiphenyl-2,2'-diyl) complexes exhibit intense green emissions with high quantum efficiencies of up to 0.80 at 298 K. The emission spectral fitting and variable-temperature emission lifetime measurements indicate that the high quantum efficiency was achieved because of the tight packing structure and strong σ-donating ability of bph.

Vapochromic crystals: understanding vapochromism from the perspective of crystal engineering

Vapochromic materials, which undergo colour and/or emission changes upon exposure to certain vapours or gases, have received increasing attention recently because of their wide range of applications in, e.g., chemical sensors, light-emitting diodes, and environmental monitors. Vapochromic crystals, as a specific kind of vapochromic materials, can be investigated from the perspective of crystal engineering to understand the mechanism of vapochromism. Moreover, understanding the vapochromism mechanism will be beneficial to design and prepare task-specific vapochromic crystals as one kind of low-cost 'electronic nose' to detect toxic gases or volatile organic compounds. This review provides important information in a broad scientific context to develop new vapochromic materials, which covers organometallic or coordination complexes and organic crystals, as well as the different mechanisms of the related vapochromic behaviour. In addition, recent examples of supramolecular vapochromic crystals and metal-organic-framework (MOFs) vapochromic crystals are introduced.

Luminescence of mononuclear Pt(ii) complexes with glycolate: external stimuli-induced excimer emission changes to oligomer emissions

Trihydrate crystals of novel Pt^II complexes [Pt^II(bpy)(gl)] (bpy: 2,2′-bipyridine; Hgl⁻: glycolate) show excimer emission changes to two kinds of oligomer emissions depending on the type of external stimuli.

Formation of Hetero-binuclear Pt(II)-M(II) Complexes Based on (2-(1 H-Tetrazol-5-yl)phenyl)diphenylphosphine Oxide for Superior Phosphorescence of Monomers

Novel hetero-binuclear platinum complexes (HBC-Pt(II)-M(II), M = Ca(II), Mg(II), Zn(II), and Cd(II)) have been synthesized by the reaction of the corresponding precursors [Pt(ppy)(μ-Cl)]₂ with (2-(1 H-tetrazol-5-yl)phenyl)diphenylphosphine oxide (TTPPO). The X-ray structures of the complexes show that two ancillary ligands TTPPO in the square-planar Pt(II) moiety act as a quadridentate chelating agent for the other metal center, eventually forming a distorted octahedral configuration. There are no significant π-π interactions and Pt-M metallophilic interactions in the crystal lattice, due to the steric hindrances associated with the rigid octahedral structure together with the bulky TTPPO. Consequently, HBC-Pt-M complexes show monomer emission characteristics with quantum yields up to 59% in powder, suggesting their great potential for practical applications. DFT and TD-DFT calculations on HBC-Pt-Zn reveal that the phosphorescence can be ascribed to intraligand charge transfer (³ILCT) combined with some metal-to-ligand charge transfer (³MLCT) in the Pt(ppy) moiety, which is consistent with the observations from the photophysical investigations.

Anionic cyclometalated Pt(ii) and Pt(iv) complexes respectively bearing one or two 1,2-benzenedithiolate ligands

Novel anionic cyclometalated Pt(ii) square-planar complexes NBu4[(C^N)PtII(S^S)], containing 2-phenylpyridine H(PhPy), 2-(2,4-difluorophenyl)-pyridine H(F2PhPy) and benzo[h]quinoline H(Bzq), respectively, as a cyclometalated ligand and the dianionic 1,2-benzenedithiolate (Thio)2- fragment as an (S^S) ligand, were synthesised. By the simple addition of an equivalent of (Thio)2- to the NBu4[(C^N)PtII(Thio)] complexes, octahedral anionic NBu4[(C^N)PtIV(Thio)2] analogues were obtained, representing, to the best of our knowledge, the first examples of Pt(iv) anionic cyclometalated complexes. The molecular structures of the obtained complexes in the case of the NBu4[(Bzq)PtII(Thio)] and the NBu4[(Bzq)PtIV(Thio)2] complexes were confirmed by single crystal X-ray diffraction analysis. Furthermore, the electrochemical and photophysical properties of the two series of Pt(ii) and Pt(iv) newly synthesised complexes were studied and DFT and TD-DFT calculations were performed in order to comprehensively investigate the displayed behaviour. All Pt(ii) and Pt(iv) complexes show intense luminescence in the solid state, with remarkable enhancement of the emission quantum yields, proving to be excellent examples of aggregation-induced emission systems.

A Trichromatic and White-Light-Emitting MOF Composite for Multi-Dimensional and Multi-Response Ratiometric Luminescent Sensing

Present here is a new dual ratiometric luminescent probe D which is a trichromatic and white-light-emitting metal-organic framework (MOF) composite facilely obtained by incorporating red/green-emitting complex modules into a blue-emitting MOF. Probe D exhibits remarkable capabilities of sensing different volatile organic solvents (VOSs) via 2D code recognition of the two VOS-dependent MOF ligand-to-module ratios of the emission-peak intensities. For specific VOSs, the resultant luminescent color changes from the starting white color are sharp enough to be visible to the naked eye. Remarkably, D can differentiate solution-phase nitroaromatics and metal ions by recording the evolution of the two ratios during titration processes, enabling an unusual 3D code recognition using the titrant amount as the third dimension for the first time. D also can be used to detect dinoseb, Fe³⁺ and Al³⁺ ions quantitatively by analysis of the ratios with detection limits as low as 0.050, 0.41, and 0.12 ppm, respectively. Clearly, such a self-referencing trichromatic probe can maximize the output information and significantly enhance the detection selectivity and sensitivity via multi-dimensional sensing, and has great potentials for practical applications.

Directional Self-Sorting with Cucurbit[8]uril Controlled by Allosteric π-π and Metal-Metal Interactions

To maximize Coulombic interactions, cucurbit[8]uril (CB[8]) typically forms ternary complexes that distribute the positive charges of the pair of guests (if any) over both carbonylated portals of the macrocycle. We present here the first exception to this recognition pattern. Platinum(II) acetylides flanked by 4'-substituted terpyridyl ligands (tpy) form 2:1 complexes with CB[8] in an exclusively stacked head-to-head orientation in a water/acetonitrile mixture. The host encapsulates the pair of tpy substituents, and both positive Pt centers sit on top of each other at the same CB[8] rim, leaving the other rim free of any interaction with the guests. This dramatic charge imbalance between the CB[8] rims would be electrostatically penalizing, were it not for allosteric π-π interactions between the stacked tpy ligands, and possible metal-metal interactions between both Pt centers. When both tpy and acetylides are substituted with aryl units, the metal-ligand complexes form 2:2 assemblies with CB[8] in aqueous medium, and the directionality of the assembly (head-to-head or head-to-tail) can be controlled, both kinetically and thermodynamically.

Vapochromic behavior of MOF for selective sensing of ethanol

A MOF material, Co₃[Co(CN)₆]₂ nanoparticles has been prepared for the effective detection of ethanol in vapor phase. When exposed to ethanol vapor, the material was changed from pink to purple, which is easily observed by naked eyes directly. We propose that the ethanol response is due to ethanol molecules entering the pores of the solid, where they alter the coordination geometry, leading to conversion of their Co centers from octahedral to tetrahedral coordination. Significantly, the change is reversible, which make the material reusable without subjecting to dynamic vacuum or slightly warming.

Unique Hydration/Dehydration-Induced Vapochromic Behavior of a Charge-Transfer Salt Comprising Viologen and Hexacyanidoferrate(II)

We successfully prepared and crystallographically characterized the first intermolecular charge-transfer (CT)-based vapochromic compound, (EV)(H₃O)₂[Fe(CN)₆] (1-Wet, EV²⁺: 1,1'-diethyl-4,4'-bipyridine-1,1'-diium), an ethyl viologen-containing CT salt. 1-Wet, which is purple in color, is transformed into a brown powder (1-Dry) upon exposure to methanol vapor, drying over silica gel, or heating; 1-Dry returns to 1-Wet upon exposure to water vapor. These color changes are induced by hydration and dehydration, and gravimetric analyses suggest that 1-Dry is the dehydrated form of 1-Wet, namely, (EV)(H)₂[Fe(CN)₆]. Interestingly, desorption of water molecules from the oxonium ions in 1-Wet produces isolated protons (H⁺) that remain in 1-Dry as counter cations. Powder X-ray crystal structure analysis of 1-Dry reveals the presence of very short contacts between the nitrogen atoms of adjacent [Fe(CN)₆]^4- anions in the crystal. The isolated protons are trapped between the nitrogen atoms of cyanido ligands to form very short N···H···N hydrogen bonds. A detailed comparison of the crystal structures of 1-Wet and 1-Dry reveals that hydration and dehydration induce changes in crystal packing and intermolecular CT interactions, resulting in reversible color changes.

Luminescent ionic liquids based on cyclometalated platinum(ii) complexes exhibiting thermochromic behaviour in different colour regions

Luminescent ionic liquids, based on anionic Pt(ii) complexes, were developed.

A rapidly-reversible absorptive and emissive vapochromic Pt(II) pincer-based chemical sensor

Selective, robust and cost-effective chemical sensors for detecting small volatile-organic compounds (VOCs) have widespread applications in industry, healthcare and environmental monitoring. Here we design a Pt(II) pincer-type material with selective absorptive and emissive responses to methanol and water. The yellow anhydrous form converts reversibly on a subsecond timescale to a red hydrate in the presence of parts-per-thousand levels of atmospheric water vapour. Exposure to methanol induces a similarly-rapid and reversible colour change to a blue methanol solvate. Stable smart coatings on glass demonstrate robust switching over 10⁴ cycles, and flexible microporous polymer membranes incorporating microcrystals of the complex show identical vapochromic behaviour. The rapid vapochromic response can be rationalised from the crystal structure, and in combination with quantum-chemical modelling, we provide a complete microscopic picture of the switching mechanism. We discuss how this multiscale design approach can be used to obtain new compounds with tailored VOC selectivity and spectral responses.

Cyclometalated Platinum(II) Cyanometallates: Luminescent Blocks for Coordination Self-Assembly

A family of cyanide-bridged heterometallic aggregates has been constructed of the chromophoric cycloplatinated metalloligands and coordinatively unsaturated d¹⁰ fragments {M(PPh₃)_n}. The tetranuclear complexes of general composition [Pt(C^N)(CN)₂M(PPh₃)₂]₂ [C^N = ppy, M = Cu (1), Ag (2); C^N = tolpy (Htolpy = 2-(4-tolyl)-pyridine), M = Cu (4), Ag (5); C^N = F₂ppy (HF₂ppy = 2-(4, 6-difluorophenyl)-pyridine), M = Cu (7), Ag (8)] demonstrate a squarelike arrangement of the molecular frameworks, which is achieved due to favorable coordination geometries of the bridging ligands and the metal ions. Variation of the amount of the ancillary phosphine (for M = Ag) afforded compounds [Pt(C^N)(CN)₂Ag(PPh₃)]₂ (C^N = ppy, 3; C^N = tolpy, 6); for the latter one an alternative cluster topology, stabilized by the Pt-Ag metallophilic and η¹-C_ipso(C^N)-Ag bonding, was observed. The solid-state structures of all of the title species 1-8 were determined crystallographically. The complexes exhibit moderately strong room-temperature phosphorescence as crystalline powders (Φ_em = 16-34%, λ_em = 470-511 nm). The luminescence studies and time-dependent density functional theory computational analysis indicate that the photophysical behavior is dominated by the ³π-π* electronic transitions localized on the cyclometalated fragment and mixed with M_PtLCT contribution, while the d¹⁰-phosphine motifs have a negligible contribution into the frontier orbitals and therefore show a little influence on the emission performance of the described compounds.

Anionic cyclometallated Pt(ii) square-planar complexes: new sets of highly luminescent compounds

Novel anionic Pt(ii) complexes were synthesized, displaying an outstanding enhancement of the emission efficiency in the solid state.

White Light Emission from Planar Remote Phosphor Based on NHC Cycloplatinated Complexes

We report on the generation of bright white luminescence through solid-state illumination of remote phosphors based on novel cycloplatinated N-heterocyclic carbene (NHC) compounds. Following a stepwise protocol we got the new NHC compound [{Pt(μ-Cl)(C(∧)C*)}2] (4) (HC(∧)C*-κC* = 1-(4-(ethoxycarbonyl)phenyl)-3-methyl-1H-imidazol-2-ylidene), which was used together with the related ones 4a (HC(∧)C*-κC*= 1-(4-cyanophenyl)-3-methyl-1H-imidazol-2-ylidene) and 4b (HC(∧)C*-κC*= 3-methyl-1-(naphthalen-2-yl)-1H-imidazol-2-ylidene) as starting materials for the synthesis of the new ionic derivatives [Pt(R-C(∧)C*) (CNR')2]PF6 (R = -COOEt, R' = t-Bu (5), Xyl (6); R = -CN, R' = t-Bu (7), Xyl (8); R(∧)C = Naph, R' = t-Bu (9), Xyl (10)). The X-ray structures of 6 and 8-10 have been determined. The photophysical properties of these cationic compounds have been studied and supported by the time-dependent-density functional theory (TD-DFT) calculations. The compounds 5, 8, and 9 have been revealed as the most efficient emitters in the solid state with quantum yields of 41%, 21%, and 40%, respectively. White-light remote-phosphors have been prepared just by stacking different combinations of these compounds and [Pt(bzq) (CN) (CN(t)Bu)] (R1) as blue (5, 8), yellow (9), and red (R1) components onto the same substrate. The CCT (correlated color temperature) and the CRI (color rendering index) of the emitted white-light have been tuned by accurately controlling the individual contributions.

Shape-Memory Platinum(II) Complexes: Intelligent Vapor-History Sensor with ON-OFF Switching Function

A novel platinum(II)-diimine complex, [Pt(CN)2 (H2 dcphen)] (1; H2 dcphen=4,7-dicarboxy-1,10- phenanthroline), was synthesized and its vapochromic shape-memory behavior was evaluated. The as-synthesized amorphous purple solid, [Pt(CN)2 (H2 dcphen)]⋅2 H2 O (1 P), exhibited vapochromic behavior in the presence of alcoholic vapors through transformation to a red, crystalline, porous, vapor-adsorbed form, 1 R⊃vapor. The obtained 1 R⊃vapor complex released the adsorbed vapors upon heating without collapse of the porous structure. The vaporfree, porous 1 R⊃open could detect water or n-hexane vapor, although these vapors could not induce 1 P-to-1 R⊃vapor transformation, and 1 R⊃open could easily be converted to the initial 1 P by manual grinding. These results indicate that 1 is a new shape-memory material that functions through formation and collapse of the porous framework with an emission change upon vapor-adsorption and grinding; this enables it to exhibit vapor history and ON-OFF switching sensing functions.

Proton-switchable vapochromic behaviour of a platinum(ii)–carboxy-terpyridine complex

We synthesized a carboxy-functionalized Pt(ii)–terpyridine complex that exhibits vapochromic behavior that is switchable via protonation/deprotonation of the carboxy group.

A dual-emissive ionic liquid based on an anionic platinum(ii) complex

A dual-emissive ionic liquid of a cyclometalated platinum(ii) complex has been reported for the first time.

Photophysical and DFT studies on cycloplatinated complexes: modification in luminescence properties by expanding of π-conjugated systems

The luminescent properties of cycloplatinated complexes containing aryl and SMe₂ ligands, [Pt(p-MeC₆H₄)(ĈN)(SMe₂)], (ĈN = benzo[h]quinolate (bzq), 1, or 2-phenylpyridinate (ppy), 2), were investigated in solution and solid state.

Why do the luminescence maxima of isostructural palladium(II) and platinum(II) complexes shift in opposite directions?

Temperature-dependent luminescence spectra for a series of palladium(II) and platinum(II) complexes with thiocyanate, halide, and dithiocarbamate ligands are presented. All complexes show broad d−d luminescence. Crystal structures are reported for (n-Bu4N)2[Pt(SCN)4] and (n-Bu4N)2[Pd(SCN)4] at 150 and 250 K, for the palladium(II) dimethyldithiocarbamate (MeDTC) complex [Pd(MeDTC)2] at 150 and 300 K, and for its platinum(II) analog at 100 and 300 K. The structures of (n-Bu4N)2[Pt(SCN)4], (n-Bu4N)2[Pd(SCN)4], and [Pt(MeDTC)2] show similar volume increases with temperature. In contrast, the luminescence band maxima of palladium(II) and platinum(II) complexes have opposite shifts with increasing temperature. (n-Bu4N)2[Pd(SCN)4] shows a shift of −2.0 cm−1/K and [Pd(MeDTC)2] a shift of −1.1 cm−1/K, while both platinum(II) complexes have a positive shift of +1.6 cm−1/K. Calculated luminescence spectra with adjustable parameters reproduce the experimental spectra. The variation of their parameters with temperature shows the origin of different trends. Temperature-dependent luminescence spectra of [Pd(SCN)4]2− and [Pt(SCN)4]2− in polymer films of polyvinyl alcohol were measured. No clearcut shifts of maxima were observed for either compound, and their spectra are broader due to the disordered environment.

Thermo- and mechanical-grinding-triggered color and luminescence switches of the diimine-platinum(II) complex with 4-bromo-2,2'-bipyridine

The square-planar diimine-platinum(II) complex, Pt(4-Brbpy)(C≡CC6H5)2 (1) (4-Brbpy = 4-bromo-2,2'-bipyridine), was prepared and characterized. Solid-state 1 exhibits reversible thermo- and mechanical-grinding-triggered color and luminescence changes. When crystalline 1·2(CH2Cl2) or 1·2(CHCl3) are heated or ground, the original bright yellow-green emission centered at 525 (549, sh) nm changed to 637 and 690 nm, corresponding to thermo- and mechanochromic response shifts of approximately 88-112 nm and 141-165 nm, respectively. Meanwhile the crystalline state changes into an amorphous phase in both processes. Once the amorphous sample absorbs organic vapors, it can be reverted to the original crystalline state, along with red luminescence turning back to yellow-green emission. The reversibility of thermo- and mechanical-grinding-triggered chromic luminescence properties has been dynamically monitored by emission spectra and X-ray diffraction patterns. The dramatic thermo- and mechanical-grinding-triggered emission red shifts are most likely due to the conversion of the (3)MLCT/(3)LLCT emission state into the (3)MMLCT triplet state.