Photophysical properties of Pt(ii) complexes based on the benzoquinoline (bzq) ligand with OLED implication: a theoretical study

In this study, we investigate photophysical properties of eight inorganic Pt(ii) complexes containing the bzq (benzoquinoline) ligand for OLED applications using high-level density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations. We explore the radiative and non-radiative relaxation constants (k r, k nr), spin-orbit coupling (SOC) matrix elements, and spectral properties. To ensure compatibility between the host and guest compounds, we determine the HOMO and LUMO energy levels, as well as the triplet excitation energies of the selected systems, and evaluate their efficiency for OLED devices. Our findings indicate that all systems, except for 2a and 2b, exhibit a small S1-T1 energetic gap (ΔE ≤ 0.60 eV) and promising SOC matrix elements (25-93 cm-1), leading to a significant intersystem crossing (ISC) process. These complexes also show promising radiative relaxation rates (k r = ∼10-4 s-1) and high phosphorescent quantum yields (Φ > 30%). Thus, our results confirm that six out of the eight selected Pt(ii) complexes are promising candidates for use in the emitting layer (EML) of OLED devices as efficient green emitters.

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.

DFT/TD-DFT study of electronic and phosphorescent properties in cycloplatinated complexes: implications for OLEDs

High level density functional and time-dependent density functional (DFT, TD-DFT) theoretical methods have been employed to investigate the photophysical properties of 5 inorganic compounds resulting from Pt(ii) and ppy (2-phenyl-pyridine) ligands. This study is intended to provide insight into the capability of the selected systems to be used in OLED devices. In addition to an exploration of their ground and excited state geometry and electronic structures, the electronic transitions responsible for their absorption and spectra, as well as other photophysical properties, have been analyzed. To this end, their charge transfer parameters, the triplet exciton generation, phosphorescence quantum yield, and radiative decay rates have been studied. Overall, the results confirm that the selected systems are promising candidates to be used in OLED devices. Moreover, the results of this study assist in understanding the photophysical properties of Pt(ii) complexes with ppy ligands.

Proton-electron-coupled functionalities of conductivity, magnetism, and optical properties in molecular crystals

Proton-electron-coupled reactions, specifically proton-coupled electron transfer (PCET), in biological and chemical processes have been extensively investigated for use in a wide variety of applications, including energy conversion and storage. However, the exploration of the functionalities of the conductivity, magnetism, and dielectrics by proton-electron coupling in molecular materials is challenging. Dynamic and static proton-electron-coupled functionalities are to be expected. This feature article highlights the recent progress in the development of functionalities of dynamic proton-electron coupling in molecular materials. Herein, single-unit conductivity by self-doping, quantum spin liquid state coupled with quantum fluctuation of protons, switching of conductivity and magnetism triggered by the disorder-order transition of deuterons, and their external responses under pressure and in the presence of an electric field are introduced. In addition, as for the functionalities of proton-d/π-electron coupling in metal dithiolene complexes, magnetic switching with multiple PCET and vapochromism induced by electron transfer through hydrogen-bond (H-bond) formation is introduced experimentally and theoretically. We also outlined the basic and applied issues and potential challenges for development of proton-electron-coupled molecular materials, functionalities, and devices.

Chelating and Bridging Roles of 2-(2-Pyridyl)benzimidazole and Bis(diphenylphosphino)acetylene in Stabilizing a Cyclic Tetranuclear Platinum(II) Complex

The reaction of complex [Pt(Me)(DMSO)(pbz)], 1, (pbz = 2-(2-pyridyl)benzimidazolate) with [PtMe(Cl)(DMSO)₂], B, followed by addition of bis(diphenylphosphino)acetylene (dppac), gave the novel tetranuclear platinum complex [Pt₄Me₄(μ-dppac)₂(pbz)₂Cl₂], 2, bearing both the pbz and dppac ligands. In this structure, the pbz ligands are both chelating and bridging to stabilize the tetraplatinum framework. The tetranuclear Pt(II) complex was fully characterized by NMR spectroscopy, X-ray crystallography, and mass spectrometry, and its electronic structure was investigated and supported by DFT calculations.

The influence of thiolate ligands on the luminescence properties of cycloplatinated(ii) complexes

Complexes [Pt(C^{^}N)(PPh₃)Cl] (C^{^}N = bzq (7,8-benzoquinolinyl, A) and ppy (2-phenylpyridinyl, B)) were reacted with various thiolate ligands to afford complexes [Pt(C^{^}N)(PPh₃)(κ¹-S-SR)], C^{^}N = bzq, R = SPh (thiophenolate, 1a); C^{^}N = ppy, R = SPh (1b); C^{^}N = bzq, R = Spy (pyridine-2-thiolate, 2a); C^{^}N = ppy, R = Spy (2b); C^{^}N = bzq, R = SpyN (pyrimidine-2-thiolate, 3a); C^{^}N = ppy, R = SpyN (3b). Complexes 1-3 were characterized by NMR spectroscopy, and the solid-state structures of 1a and 2a were determined by X-ray diffraction methods. Replacing a chloride ligand with electron-rich thiolates changes the lowest energy singlet and triplet excited states to the ones that feature charge transfer from the thiolate (mixed with some metal character) to the C^{^}N ligand, which was supported by TD-DFT calculations. All complexes are emissive at 298 K in the solid state except 2b and 3b, which are emissive only at 77 K having a less rigid structure compared to others. The emission of 1a and 1b originates from a low-energy excited state of d_Pt/π_SR → π*_C^N while 3a exhibits a ³LC/³MLCT transition. For 1a and 1b, the radiative rate and the quantum efficiency are higher in a rigid environment such as a solid compared to a polymer and solution. Decreasing the rigidity of the environment leads to a flexibility of rotation of the -SR around the axis of the Pt-S bond. So the geometry can be easily changed after radiation and the lowest lying triplet excited state would have the effective contribution of the dd* transition, which opens a nonradiative pathway at room temperature.

Cyclometalated platinum(ii) complexes of 2,2'-bipyridine N-oxide containing a 1,1'-bis(diphenylphosphino)ferrocene ligand: structural, computational and electrochemical studies

The preparation and characterization of new heteronuclear-platinum(ii) complexes containing a 1,1'-bis(diphenylphosphino)ferrocene (dppf) ligand are described. The reaction of the known starting complex [PtMe(κ²N,C-bipyO-H)(SMe₂)], A, in which bipyO-H is a cyclometalated rollover 2,2'-bipyridine N-oxide, with the dppf ligand in a 2 : 1 ratio or an equimolar ratio led to the formation of the corresponding binuclear complex [Pt₂Me₂(κ²N,C-bipyO-H)₂(μ-dppf)], 1, or the mononuclear complex [PtMe(κ¹C-bipyO-H)(dppf)], 2, respectively. According to the reaction conditions, the dppf ligand in 1 and 2 behaves as either a bridging or chelating ligand. All complexes were characterized by NMR spectroscopy. The solid-state structure of 2 was determined by the single-crystal X-ray diffraction method and it was shown that the chelating dppf ligand in this complex was arranged in a "synclinal-staggered" conformation. Also, the occurrence of intermolecular C-H_CpO_bipyO-H interactions in the solid-state gave rise to an extended 1-D network. The electronic absorption spectra and the electrochemical behavior of these complexes are discussed. Density functional theory (DFT) was used for geometry optimization of the singlet states in solution and for electronic structure calculations. The analysis of the molecular orbital (MO) compositions in terms of occupied and unoccupied fragment orbitals in 2 was performed.

Reactivity of a new aryl cycloplatinated(ii) complex containing rollover 2,2′-bipyridine N-oxide toward a series of diphosphine ligands

A new rollover cycloplatinated(ii) complex was prepared. The reactivity of this complex was investigated towards a wide range of diphosphine ligands.

Cycloplatinated(ii) complexes bearing an O,S-heterocyclic ligand: search for anticancer drugs

Cycloplatinated(ii) complexes containing the 2-mercaptopyridine N-oxide ligand were synthesized and characterized spectroscopically. The biological activities of these complexes were also investigated.

Influence of ancillary ligands on the photophysical properties of cyclometalated organoplatinum(ii) complexes

The photophysical properties of three series of cyclometalated organoplatinum(ii) complexes were studied and the influence of changing the ancillary ligands and substituents on their luminescence properties were investigated.

Photophysical properties of a series of cycloplatinated(ii) complexes featuring allyldiphenylphosphane

Cycloplatinated(ii) complexes 1–4 were synthesized and characterized. All complexes exhibit strong luminescence except 3.

Photophysical study on unsymmetrical binuclear cycloplatinated(ii) complexes

A general synthetic method has been designed to prepare a new series of unsymmetrical binuclear cyclometalated organoplatinum(ii) complexes and the effect of each part on their luminescence properties were investigated.

A new approach to the effects of isocyanide (CN-R) ligands on the luminescence properties of cycloplatinated(ii) complexes

Cycloplatinated complexes bearing isocyanides were prepared and characterized. The complexes exhibited strong luminescence while the nature of R substituents in isocyanides affected the luminescence characteristics.

Phosphorescent heterobimetallic complexes involving platinum(iv) and rhenium(vii) centers connected by an unsupported μ-oxido bridge

Heterobimetallic compounds containing an unsupported Pt(iv)–O–Re(vii) bridge are synthesized. The complexes exhibit rare phosphorescence emission in solid and frozen states.

Luminescence properties of some monomeric and dimeric cycloplatinated(ii) complexes containing biphosphine ligands

The starting complexes [PtCl(C^N)(dmso)], in which C^N is either ppy = 2-phenylpyridinate, , or bhq = 7,8-benzo[h]quinolinate, , were prepared by a known method using the reaction of [PtCl2(dmso)2] with ppyH or bhqH, respectively, in toluene under reflux conditions. The reaction of [PtCl(C^N)(dmso)], or , with 1 equiv. of a number of biphosphine ligands, P^P, gave the cationic monomeric complexes [Pt(ppy)(P^P)]Cl, for which P^P is either 1,2-bis(diphenylphosphino)ethane (dppe), , 1,3-bis(diphenylphosphino)propane (dppp), , or bis(diphenylphosphino)methane (dppm), ; the bhq analogous complex [Pt(bhq)(dppe)]Cl, , was prepared similarly. However, the complex [Pt(ppy)(dfppe)]Cl, , in which dfppe is 1,2-bis(dipentafluorophenylphosphino)ethane, was prepared by the reaction of with excess amount of dfppe. When each of the starting complexes [PtCl(C^N)(dmso)], or , were reacted with 0.5 equiv. of any of the P^P ligands, the dimeric complexes [Pt2Cl2(ppy)2(μ-P^P)], , or [Pt2Cl2(bhq)2(μ-P^P)], , were formed. The complexes were fully characterized using multinuclear ((1)H and (31)P) NMR spectroscopy and elemental analysis. The structures of typical complexes , , , and were also confirmed by X-ray crystallography. The effect of ligands on the luminescent properties of the complexes was investigated and DFT calculations were performed to confirm the assignments.