Platinum complexes with aggregation-induced emission

Transition metal-containing materials with aggregation-induced emission (AIE) have brought new opportunities for the development of biological probes, optoelectronic materials, stimuli-responsive materials, sensors, and detectors. Coordination compounds containing the platinum metal have emerged as a promising option for constructing effective AIE platinum complexes. In this review, we classified AIE platinum complexes based on the number of ligands. We focused on the development and performance of AIE platinum complexes with different numbers of ligands and discussed the impact of platinum ion coordination and ligand structure variation on the optoelectronic properties. Furthermore, this review analyzes and summarizes the influence of molecular geometries, stacking models, and aggregation environments on the optoelectronic performance of these complexes. We provided a comprehensive overview of the AIE mechanisms exhibited by various AIE platinum complexes. Based on the unique properties of AIE platinum complexes with different numbers of ligands, we systematically summarized their applications in electronics, biological fields, etc. Finally, we illustrated the challenges and opportunities for future research on AIE platinum complexes, aiming at giving a comprehensive summary and outlook on the latest developments of functional AIE platinum complexes and also encouraging more researchers to contribute to this promising field.

Polymorphism and Mechanochromism in 2-Phenylbenzothiazole Cyclometalated PtII Complexes with Chelating N∧O Ligands

New cyclometalated Pt^II complexes with 2-phenylbenzothiazole (pbt) and two different picolinate ligands [Pt(pbt)(R-pic-κN,O)] (R = H (1), OH (2)) were prepared. In contrast to 1, the OH substituent group on 2 allows modulation of the packing in the solid state through donor-acceptor H-bonding interactions with the CH₂Cl₂ solvent. Thus, three pseudopolymorphs of 2 with different aggregation degrees were isolated, including yellow 2-Y, orange-red 2-R (2·0.5CH₂Cl₂) and black 2-B (2·0.75CH₂Cl₂) with emissions at 540, 656, and 740 nm, respectively, in the solid state at 298 K. 2-R and 2-B can be transformed to the pristine solid 2. Studies of their crystal structures show that 1 and 2-Y stack in columns with only π···π stacking interactions, whereas 2-R displays strong aggregated 1D infinite chains based on Pt···Pt and π···π stacking interactions, consistent with the colors and the photophysical properties, measured in several media. Interestingly, 1 and 2 exhibit reversible mechanochromic behavior with high contrast in the color and color emission upon mechanical grinding due to a phase transition between a crystalline and an amorphous state, as confirmed by powder X-ray diffraction (PXRD) studies. Theoretical calculations indicate that Pt···Pt contacts are more relevant in the trimers and tetramers than in the dimers, particularly in their T₁ states, associated with a change from a ³IL/³MLCT transition in the monomer to ³MM(L+L')CT in the oligomers. Noncovalent interaction (NCI) theoretical studies indicate that the π···π stacking among chelates also exerts a strong influence in the metal-metal-to-ligand charge transfer transition character.

Emergence of practical fluorescence in a confined space of nanoporous silica: significantly enhanced quantum yields of a conjugated molecule

The fluorescence of benzanthrone, which is a conjugated molecule bearing a carbonyl group, is activated by confinement in a pore with a diameter close to the molecular size. An intense emission originating from the aromatic character π-π* transition is achieved through suppression of the nonradiative n-π* transition by strong hydrogen bonding between carbonyl groups and silanol groups with a micropore-filling effect in the nanospace.

Photophysical Properties of Cyclometalated Platinum(II) Diphosphine Compounds in the Solid State and in PMMA Films

Platinum(II) compounds were synthesized with both chelate cyclometalated ligands and chelate diphosphine ligands. The cyclometalated ligands include phenylpyridine and a benzothiophene-containing ligand. The three new benzothiophene compounds were characterized by nuclear magnetic resonance (NMR) spectroscopy, high-resolution mass spectrometry (HR-MS), and photophysical measurements. In the case of one compound, L1-DPPM, the structure was determined by single crystal X-ray diffraction. The structural coherence of the noncrystalline emissive solid state was measured by X-ray total scattering real space pair distribution function analysis. Quantum yield values of all of the platinum compounds measured in the solid state and in PMMA films were much greater than in solution.

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.

Simple ratiometric push–pull with an ‘aggregation induced enhanced emission’ active pyrene derivative: a multifunctional and highly sensitive fluorescent sensor

A simple and efficient pyrene based luminescent multifunctional probe was utilized in selective and sensitive ratiometric detection of H⁺, Al³⁺ and picric acid.

Solvent-tuned charge-transfer properties of chiral Pt(ii) complex and TCNQ˙− anion adducts

A new pair of adducts comprising one chiral Pt(ii) complex cation, [Pt((−)-L₁)(Dmpi)]⁺ ((−)-1) or [Pt((+)-L₁)(Dmpi)]⁺ ((+)-1) [(−)-L₁ = (−)-4,5-pinene-6′-phenyl-2,2′-bipyridine, (+)-L₁ = (+)-4,5-pinene-6′-phenyl-2,2′-bipyridine, Dmpi = 2,6-dimethylphenylisocyanide], together with one TCNQ˙⁻ anion have been obtained, and the structures have been confirmed via single-crystal X-ray crystallography and infrared (IR) spectroscopy. The chiral Pt(ii) cation and TCNQ˙⁻ anion are dissociated in MeOH solution, while charge transfer adducts are formed in H₂O solution, leading to perturbation of the electronic structure and alteration of the chiral environment, as evidenced by the differences in the UV-vis absorption and electronic circular dichroism spectra. The solvent-tuned charge-transfer properties also have been validated through emission and resonance light scattering spectra. The interesting findings may have potential applications in the development of black absorbers and wide band gap semiconductors.

A new couple of charge transfer adducts comprising of one chiral Pt(ii) complex cation together with one TCNQ˙⁻ anion have been prepared, and solvent-induced variances of absorption, luminescence as well as chiral spectra have been investigated.