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

Controlled crystallisation of porous crystals of luminescent platinum(II) complexes by electronic tuning of ancillary ligands

Porous molecular crystals (PMCs) have gained significant importance as next-generation functional porous materials. However, the selective crystallisation of the PMC phase remains a challenge. Herein, we have systematically controlled the stability of the luminescent PMC phase prepared using the luminescent Pt(II) complex [Pt(pbim)(N^O)] (pbim = 2-phenylbenzimidazolate, N^O = N-heteroaryl carboxylate) with Pt⋯Pt electronic interactions. The PMC phase formation varied significantly among the complexes depending on the heteroaryl group of the ancillary N^O ligand; the oxazolyl-bearing complex did not form a PMC phase, whereas the pyrazyl- and 5-fluoropyridyl-bearing complexes spontaneously formed a porous structure. This difference was rationalised by the π-stacking capability of the heteroaryl group of the ancillary ligand. Furthermore, owing to the presence of the one-dimensional Pt⋯Pt chains in this PMC phase, the photophysical properties of PMCs resulting from the Pt⋯Pt interactions were also significantly changed by the ancillary ligands.

Influence of O-H⋅⋅⋅Pt interactions on photoluminescent response in the (Et4N)2{[Pt(bph)(CN)2][phenylene-1,4-diresorcinol]} framework

Tunable photoluminescence (PL) is one of the hot topics in current materials science, and research performed on the molecular phases is at the forefront of this field. We present the new (Et4N)2[PtII(bph)(CN)2]⋅rez3⋅1/3H2O (Pt2rez3) (bph=biphenyl-2,2'-diyl; rez3=3,3",5,5"-tetrahydroxy-1,1':4',1"-terphenyl, phenylene-1,4-diresorcinol coformer, a linear quaternary hydrogen bond donor) co-crystal salt based on the recently appointed promising [PtII(bph)(CN)2]2- luminophore. Within the extended hydrogen-bonded subnetwork [PtII(bph)(CN)2]2- complexes and rez3 coformer molecules form two types of contacts: the rez3O-H⋅⋅⋅Ncomplex ones in the equatorial plane of the complex and non-typical rez3O-H⋅⋅⋅Pt ones along its axial direction. The combined structural, PL, and DFT approach identified the rez3O-H⋅⋅⋅Pt synthons to be crucial in promoting the noticeable uniform redshift of bph ligand centered (LC) emission compared to the LC emission of the (Et4N)2[PtII(bph)(CN)2]⋅H2O (Pt2) precursor, owing to the direct interference of the phenol group with the PtII-bph orbital system via altering the CT processes within. The high-resolution emission spectra for Pt2 and Pt2rez3 were successfully reproduced at 77 K by using the Franck-Cordon expressions. The possibility to tune PL properties along the plausible continuum of rez3O-H⋅⋅⋅Pt synthons is indicated, considering various scenarios of molecular occupation of the space above and below the complex plane.

Luminescent Platinum(II) Complexes with Terdentate N∧C∧C Ligands

The synthesis, structure, and luminescence of Pt(II) complexes of the type [Pt(N∧C∧C)(L)] are reported, where N∧C∧C is a terdentate ligand resulting from the cycloplatination of 2-(3,5-diphenoxyphenyl)pyridine or 2-(4,4″-dimethyl-[1,1':3',1″-terphenyl]-5'-yl)pyridine, and L represents a monodentate ancillary ligand, which can be γ-picoline, 4-pyridinecarboxaldehyde, PPh3, n-butyl or 2,6-dimethylphenyl isocyanide, CO, or the N-heterocyclic carbenes 1-butyl-3-methylimidazol-2-ylidene or 4-butyl-3-methyl-1-phenyl-1H-1,2,3-triazol-5-ylidene. Derivatives bearing CO, isocyanides, or carbenes showed the highest stabilities in solution, whereas the pyridine and PPh3 derivatives establish ligand-exchange equilibria in acetonitrile. Different supramolecular structures are observed in the solid state, which largely depend on the nature of the ancillary ligand. Isocyanides and CO favor π interactions between the aromatic rings, metallophilic Pt···Pt contacts, or a combination of both. In contrast, pyridine ligands may lead to bimolecular assemblies driven by C-H···O, C-H···Pt, or C-H/π hydrogen bonds. Luminescence was examined in fluid solution, poly(methyl methacrylate) matrices, and the solid state at 298 K, and in 2-methyltetrahydrofuran glasses at 77 K. The majority of derivatives show highly efficient emissions from 3ILCT/MLCT or 3ILCT/MLCT/LLCT excited states of monomeric species. The formation of excimers and different types of emissive aggregates are demonstrated, which lead to red-shifted emissions of different origins and characteristics depending on the involved noncovalent interactions.

Phosphorescent biaryl platinum(IV) complexes obtained through double metalation of dibenzoiodolium ions

The first series of neutral, tris-chelate, phosphorecent Pt(IV) complexes is reported, which combine two cyclometalated 2-arylpyridine ligands and a dimetalated biaryl. The introduction of biaryl ligands is achieved under mild conditions through the oxidative addition of dibenzoiodolium ions to Pt(II) precursors to give Pt(IV) intermediates with a singly metalated 2-(2-iodoaryl)aryl ligand, followed by the reductive metalation of the C-I bond. The modulation of emission characteristics via derivatization of both types of ligands is demonstrated.