Cyclometalated platinum(II) complexes with acyclic diaminocarbene ligands for OLED application

Unveiling mechanistic insights and applications of aggregation-enhanced emission (AEE)-active polynuclear transition metal complexes

Aggregation-enhanced emission (AEE) in polynuclear transition metal complexes (PTMCs) represents a major advancement in luminescent materials, overcoming the limitations of aggregation-caused quenching (ACQ) in traditional systems. Unlike conventional materials that suffer from quenching, AEE-active PTMCs exhibit enhanced luminescence in the aggregated state, driven by mechanisms such as restricted molecular motion, π-π stacking, and metal-metal interactions. These properties make PTMCs highly versatile for applications including chemical sensing, bioimaging, photodynamic therapy (PDT), optoelectronics (e.g., OLEDs, WOLEDs, and LEDs), and security technologies (e.g., anti-counterfeiting inks). They enable the sensitive detection of pollutants, facilitate high-performance bioimaging, and enhance the efficiency of energy devices. However, PTMCs face several challenges, including complex synthesis, limited thermal and photostability, solubility issues, and environmental and toxicity concerns. Additionally, high production costs, instability in different media, and the need for optimized energy transfer efficiency must be addressed to enhance their practical performance. This review explores the mechanisms behind AEE in PTMCs and discusses strategies for overcoming these challenges, including ligand engineering, hybrid material development, and sustainable synthesis methods. It also highlights their potential in advancing energy-efficient technologies, precision therapeutics, and secure communication systems, contributing to a more sustainable and innovative future.

Conformation-Associated C···dz2-PtII Tetrel Bonding: The Case of Cyclometallated Platinum(II) Complex with 4-Cyanopyridyl Urea Ligand

The nucleophilic addition of 3-(4-cyanopyridin-2-yl)-1,1-dimethylurea (1) to cis-[Pt(CNXyl)2Cl2] (2) gave a new cyclometallated compound 3. It was characterized by NMR spectroscopy (1H, 13C, 195Pt) and high-resolution mass spectrometry, as well as crystallized to obtain two crystalline forms (3 and 3·2MeCN), whose structures were determined by X-ray diffraction. In the crystalline structure of 3, two conformers (3A and 3B) were identified, while the structure 3·2MeCN had only one conformer 3A. The conformers differed by orientation of the N,N-dimethylcarbamoyl moiety relative to the metallacycle plane. In both crystals 3 and 3·2MeCN, the molecules of the Pt(II) complex are associated into supramolecular dimers, either {3A}2 or {3B}2, via stacking interactions between the planes of two metal centers, which are additionally supported by hydrogen bonding. The theoretical consideration, utilizing a number of computational approaches, demonstrates that the C···dz2(Pt) interaction makes a significant contribution in the total stacking forces in the geometrically optimized dimer [3A]2 and reveals the dz2(Pt)→π*(PyCN) charge transfer (CT). The presence of such CT process allowed for marking the C···Pt contact as a new example of a rare studied phenomenon, namely, tetrel bonding, in which the metal site acts as a Lewis base (an acceptor of noncovalent interaction).