Aggregation Effect on the Luminescence Properties of Phenylbipyridine Pt(II) Acetylide Complexes. A Theoretical Prediction with Experimental Evidence

Photoluminescence of Platinum(II) Complexes with Diazine-Based Ligands

In the last past twenty years, research on luminescent platinum (II) complexes has been intensively developed for useful application such as organic light emitting diodes (OLEDs). More recently, new photoluminescent complexes based on diazine ligands (pyrimidine, pyrazine, pyridazine, quinazoline and quinoxaline) have been developed in this context. This review will summarize the photophysical properties of most of the phosphorescent diazine Pt(II) complexes described in the literature and compare the results to pyridine analogues whenever possible. Based on the emission color, and the photoluminescence quantum yield (PLQY) values, the relationship between structure modification, and photophysical properties are highlighted. Tuning of emission color, quantum yields in solution and solid state and, for some complexes, aggregation induced emission (AIE) or thermally activated delayed fluorescence (TADF) properties are described. When emitting OLEDs have been built from diazine Pt(II) complexes, the external quantum efficiency (EQE) values and luminance for different emission wavelengths and in some cases, chromaticity coordinates obtained from devices, are given. Finally, this review highlights the growing interest in studies of new luminescent diazine Pt(II) complexes for OLED applications.

Controlling the Triplet Potential Energy Surface of Bimetallic Platinum(II) Complex by Constructing Structure-Property Relationship: A Theoretical Exploration

For phosphorescent materials, managing the triplet potential energy surface stands for controlling the phosphorescence quantum yield. However, due to the complexity and variability, the triplet potential energy surface can be managed with difficulty. In this work, a series of bimetallic Pt(II) complexes, namely Pt-1, Pt-1-1, Pt-1-2, Pt-2, Pt-3-5, and Pt-6-7, are employed as models to construct a relationship between the structures and triplet potential energy surfaces, aiming to achieve meaningful information to manage the triplet potential energy surface. On the basis of the results, it is observed that the triplet potential energy surface has an intimate connection with the structures of bimetallic Pt(II) complexes. In the case of the primordial Pt(II) complex, the triplet potential energy surface consists of two minimal points, illustrating various properties, which can largely affect the phosphorescence quantum yield. Once the intramolecular steric hindrance, restriction effect, and metallophilic interaction (Pt-Pd/Pd-Pd) are employed by tailoring the structures of primordial Pt(II) complexes, the triplet potential energy surface can be reconstructed via one minimal point-charactered short metal-metal distance, resulting in different photophysical properties. The relationship between the triplet potential energy surface and structure is essentially unveiled from the structural and electronic viewpoints. The conclusions originated from the structural and electronic investigations can be regarded as indicators to accurately and expediently predict the triplet potential energy surfaces of bimetallic Pt(II) complexes. The results presented here are helpful in addressing the designed strategies as they show that the triplet potential energy surfaces of bimetallic Pt(II) complexes can be properly tuned.

Luminescent Complexes of Platinum, Iridium, and Coinage Metals Containing N-Heterocyclic Carbene Ligands: Design, Structural Diversity, and Photophysical Properties

The employment of N-heterocyclic carbenes (NHCs) to design luminescent metal compounds has been the focus of recent intense investigations because of the strong σ-donor properties, which bring stability to the whole system and tend to push the d-d dark states so high in energy that they are rendered thermally inaccessible, thereby generating highly emissive complexes for useful applications such as organic light-emitting diodes (OLEDs), or featuring chiroptical properties, a field that is still in its infancy. Among the NHC complexes, those containing organic chromophores such as naphthalimide, pyrene, and carbazole exhibit rich emission behavior and thus have attracted extensive interest in the past five years, especially carbene coinage metal complexes with carbazolate ligands. In this review, the design strategies of NHC-based luminescent platinum and iridium complexes with large spin-orbit-coupling (SOC) are described first. Subsequent paragraphs illustrate the recent advances of luminescent coinage metal complexes with nucleophilic- and electrophilic-based carbenes based on silver, gold, and copper metal complexes that have the ability to display rich excited state emissions in particular via thermally activated delayed fluorescence (TADF). The luminescence mechanism and excited state dynamics are also described. We then summarize the advance of NHC-metal complexes in the aforementioned fields in recent years. Finally, we propose the development trend of this fast-growing field of luminescent NHC-metal complexes.

The mutual noncovalent interactions based on metallophilic cluster and anions: A theoretical investigation of the molecular structure and spectroscopic properties of Host–Guest complexes

The d[Formula: see text] metallophilic host clusters [Au(NHC)2][Formula: see text] [M(CN)2][Formula: see text] [Au(NHC)2][Formula: see text](NHC [Formula: see text] N-heterocyclic carbene, [Formula: see text], Ag) with high phosphorescence are synthesized recently and their phosphorescent modulation by solvents is investigated in theory. In this paper, the guest anions (F−, Cl−, Br−, NO[Formula: see text], and BF[Formula: see text] are used to elucidate their effects on metallophilic interactions and phosphorescence of hosts, and also they served as the probes to study the recognition characters of metallophilic hosts. The calculation shows that the guest anions can mutually interact with the host clusters and further, which can modulate the metallophilic Au[Formula: see text]M distances and the phosphorescence spectra of the hosts.

Phosphorescent Modulation of Metallophilic Clusters and Recognition of Solvents through a Flexible Host-Guest Assembly: A Theoretical Investigation

MP2 (Second order approximation of Møller–Plesset perturbation theory) and DFT/TD-DFT (Density functional theory/Time-dependent_density_functional_theory) investigations have been performed on metallophilic nanomaterials of host clusters [Au(NHC)₂]⁺⋅⋅⋅[M(CN)₂]⁻⋅⋅⋅[Au(NHC)₂]⁺ (NHC = N-heterocyclic carbene, M = Au, Ag) with high phosphorescence. The phosphorescence quantum yield order of clusters in the experiments was evidenced by their order of μ_S1/ΔE_S1−T1 values (μS1: S₀ → S₁ transition dipole, ∆ES1−T1: splitting energy between the lowest-lying singlet S₁ and the triplet excited state T₁ states). The systematic variation of the guest solvents (S1: CH₃OH, S2: CH₃CH₂OH, S3: H₂O) are employed not only to illuminate their effect on the metallophilic interaction and phosphorescence but also as the probes to investigate the recognized capacity of the hosts. The simulations revealed that the metallophilic interactions are mainly electrostatic and the guests can subtly modulate the geometries, especially metallophilic Au⋅⋅⋅M distances of the hosts through mutual hydrogen bond interactions. The phosphorescence spectra of hosts are predicted to be blue-shifted under polar solvent and the excitation from HOMO (highest occupied molecular orbital) to LUMO (lowest unoccupied molecular orbital) was found to be responsible for the ³MLCT (triplet metal-to-ligand charge transfer) characters in the hosts and host-guest complexes. The results of investigation can be introduced as the clues for the design of promising blue-emitting phosphorescent and functional materials.

Photoluminescence of self-assembled Ag(i) and Au(i) N-heterocyclic carbene complexes. Interplay the aurophilic, hydrogen bonding and hydrophobic interactions

The incorporation of a 2-hydroxyl group at the long alkyl chain of NHC increases the hydrogen bonding interactions and thus induces the liquid crystal phase formation for the tetra nuclear Ag–NHC complex.

TD-DFT Benchmark on Inorganic Pt(II) and Ir(III) Complexes

We report in the present paper a comprehensive investigation of representative Pt(II) and Ir(III) complexes with special reference to their one-photon absorption spectra employing methods rooted in density functional theory and its time dependent extension. We have compared nine different functionals ranging from generalized gradient approximation (GGA) to global or range-separated hybrids, and two different basis sets, including pseudopotentials for 4 iridium and 7 platinum complexes. It turns out that hybrid functionals with the same exchange part give comparable results irrespective of the specific correlation functional (i.e., B3LYP is very close to B3PW91 and PBE0 is very close to MPW1PW91). More recent functionals, such as CAM-B3LYP and M06-2X, overestimate excitation energies, whereas local functionals (BP86 -GGA-, M06-L -Meta GGA-) strongly underestimate transition energies with respect to experimental results. As expected, basis set effects are weak, and the use of a triple-ζ polarized (def2-TZVP) basis set does not significantly improve the computed excitation energies with respect to a classical double-ζ basis set (LANL2DZ) augmented by polarization functions, but it significantly raises the computational effort.

Construction and luminescence property of a highly ordered 2D self-assembled amphiphilic bidentate organoplatinum(ii) complex

A red luminescent film was constructed by self-assembly of 1-Pt from methanol. The film on a substrate, exhibiting multi-stimuli responsiveness, was further obtained.

Luminescent Pt(ii) complexes bearing dual isoquinolinyl pyrazolates: fundamentals and applications

Pt(ii) complex [Pt(Lx)₂], LxH = 6-t-butyl-1-(3-trifluoromethyl-1H-pyrazol-5-yl) isoquinoline, with three colored morphologies can be interconverted by grinding and/or wetting with solvents.

Bis(pyridylpyrazolate)platinum(ii): a mechanochromic complex useful as a dopant for colour-tunable polymer OLEDs

A novel metallomesogenic Pt(ii) dopant on the PFO-matrix allows induction of colour changes from bluish-green to orange-red with just 5% complex concentration.

Novel helical assembly of a Pt(ii) phenylbipyridine complex directed by metal–metal interaction and aggregation-induced circularly polarized emission

Pt(ii) complexes possessing phenylisoxazole moieties self-assembled to form helical stacked aggregates which display aggregation-induced circularly polarized luminescence.

Computational insights into the photodeactivation dynamics of phosphors for OLEDs: a perspective

In this perspective we highlight recent computational efforts to unravel competing photodeactivation mechanisms of radiative and non-radiative nature of phosphors.