Exploring structural and optical properties of a new series of soft salts based on cyclometalated platinum complexes

A series of nine new soft salts based on two platinum(II) complexes, namely ([Pt(C^N)(CN)2]-[Pt(C^N)(en)]+) (en = ethane-1,2-diamine), has been developed and synthesized. Their photophysical properties in both solution and the solid state were described. All soft salt complexes exhibit phosphorescence emission with PLQY in the solid state up to 0.36. Most of these materials displayed aggregation-induced emission (AIE) or aggregation-induced emission enhancement (AIEE) in water/DMSO solutions as the water ratio increased. Structure-property relationships were analyzed in relation to emission properties. The presence of the free nitrogen atoms in soft salt complexes with a C^N pyrimidine-based ligand allowed for reversible sensitivity to acidic vapors, resulting in the quenching of phosphorescence emission. Additionally, for selected soft salts, we described reversible vapochromism behaviour, making these new materials interesting for multi-detection purposes in anti-counterfeiting applications.

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.

N^N^C-Cyclometalated rhodium(III) complexes with isomeric pyrimidine-based ligands: unveiling the impact of isomerism on structural motifs, luminescence and cytotoxicity

The impact of isomerism of pyrimidine-based ligands and their rhodium(III) complexes with regard to their structures and properties was investigated. Two isomeric ligands, 4-(3,5-dimethyl-1H-pyrazol-1-yl)-2,5-diphenylpyrimidine (HL2,5) and 4-(3,5-dimethyl-1H-pyrazol-1-yl)-2,6-diphenylpyrimidine (HL2,6), were synthesized. The ligands differ by the degree of steric bulk: the molecular structure of HL2,5 is more distorted due to presence of pyrazolyl and phenyl groups in the neighbouring positions 4 and 5 of the pyrimidine ring. The complexation of HL2,5 and HL2,6 with RhCl3 leads to the sp2 C-H bond activation, resulting in the isolation of two complexes, [RhL2,5(Solv)Cl2]·nEtOH and [RhL2,6(Solv)Cl2]·nEtOH (Solv = H2O, EtOH), with the deprotonated forms of the pyrazolylpyrimidine molecules which coordinate the Rh3+ ion as N^N^C-tridentate ligands. According to DFT modelling, the mechanism of the deprotonation involves (i) the C-H bond breaking in the 2-phenyl group followed by the coordination of the C atom to the Rh atom, (ii) the protonation of coordinated chlorido ligand, (iii) the ejection of the HCl molecule and (iv) the coordination of the H2O molecule. The ligand isomerism has an impact on emission properties and cytotoxicity of the complexes. Although the excited states of the complexes effectively deactivate through S0/T1 and S0/S1 crossings associated with the cleavage of the weak H2O ligands upon excitation, the [RhL2,5(Solv)Cl2]·nEtOH complex appeared to be emissive in the solid state, while [RhL2,6(Solv)Cl2]·nEtOH is non-emissive at all. The complexes show significant cytotoxic activity against cancerous HepG2 and Hep2 cell lines, with the [RhL2,6(Solv)Cl2]·nEtOH complex being more active than its isomer [RhL2,5(Solv)Cl2]·nEtOH. On the other hand, noticeable cytotoxicity of the latter against HepG2 is supplemented by its non-toxicity against non-cancerous MRC-5 cells.

Cu(II)-Mediated Sulfonylation of (Hetero)arenes with TosMIC Using Monodentate Directing Groups

Monodentate chelation-assisted direct ortho-C-H sulfonylation of (hetero)arenes using TosMIC as the novel sulfonylating reagent has been developed. A broad range of substrates, including indolines, indoles, 2-phenylpyridines, and others were well tolerated to afford the corresponding products in moderate to good yields. Mechanistic studies revealed that the sulfonyl radical might be involved. Inspired by the above discovery, preliminary para-C-H sulfonylation of naphthalene substrate was also successfully realized. The current protocol featured with cheap metal catalysis, good functional group compatibility, and operational convenience.

The design and synthesis of green emissive iridium(III) complexes guided by calculations of the vibrationally-resolved emission spectra

A key challenge in developing emissive materials for organic light-emitting diodes is to optimize their colour saturation, which means targeting narrowband emitters. In this combined theoretical and experimental study, we investigate the use of heavy atoms in the form of trimethylsilyl groups as a tool to reduce the intensity of the vibrations in the 2-phenylpyridinato ligands of emissive iridium(III) complexes that contribute to the vibrationally coupled modes that broaden the emission profile. An underutilised computational technique, Frank-Condon vibrationally coupled electronic spectral modelling, was used to identify the key vibrational modes that contribute to the broadening of the emission spectra in known benchmark green-emitting iridium(III) complexes. Based on these results, a family of eight new green-emitting iridium complexes containing trimethylsilyl groups substituted at different positions of the cyclometalating ligands has been prepared to explore the impact that these substituents have on reducing the intensity of the vibrations and the resulting reduction in the contribution of vibrationally coupled emission modes to the shape of the emission spectra. We have demonstrated that locating a trimethylsilyl group at the N4 or N5 position of the 2-phenylpyridine ligand damps the vibrational modes of the iridium complex and provides a modest narrowing of the emission spectrum of 8-9 nm (or 350 cm^-1). The strong correlation between experimental and calculated emission spectra highlights the utility of this computational method to understand how the vibrational modes contribute to the profile of the emission spectra in phosphorescent iridium(III) emitters.

Phosphorescent cyclometalated platinum(II) complexes with phenyldiazine N^C ligands

A series of phosphorescent platinum(II) complexes containing various phenyldiazine-type bidentate N^C ligands have been successfully synthesized and characterized. Structural modifications have been made to bidentate cyclometalating ligands regarding the nature of the diazine ring (pyrimidine, pyrazine and quinazoline), the substituent groups at the C4 position of the pyrimidine ring (OCH₃, CF₃) and the EDGs at the para position of the Pt atom (OCH₃, Ph, NPh₂, carbazol). In addition, the electronic properties of the azaheterocyclic ancillary ligand have been modulated in this series of complexes (pyridine, 4-methoxy-pyridine or pyrimidine). X-ray diffraction studies have been performed on three complexes, revealing Pt(II) ions in a distorted square-planar geometrical environment with no Pt(II)⋯Pt(II) interactions but with moderate π-π interactions in the solid-state structure. Electrochemical and computational studies suggest a ligand-centered reduction on the diazine ligands with, in some cases, additional contribution from the azaheterocyclic ancillary ligand, whereas oxidation occurs on the Pt-phenyl ring substituent moieties. All complexes exhibit phosphorescence emission ranging from green to red/near-infrared, both in solution and in the solid state. Complexes bearing a 2-(3-methoxyphenyl)pyrimidine ligand show the best PLQY of the series, up to 52% in a CH₂Cl₂ solution and 20% in the solid state. Furthermore, the solid state PLQY of one of the near-infrared emitting phenylquinazoline complex has been found to be 6%.

Luminescent cyclometalated alkynylplatinum(II) complexes with 1,3-di(pyrimidin-2-yl)benzene ligands: synthesis, electrochemistry, photophysics and computational studies

In this article, we report on a series of cyclometalated chloro- and alkynyl-platinum(II) complexes bearing various tridentate N^C^N-cyclometalated ligands derived from 1,3-bis(pyrimidin-2-yl)benzene. The X-ray crystal structures of two alkynyl-platinum(II) complexes were determined and other structures were DFT-calculated. Electrochemical and DFT-computational studies suggest a ligand-centred reduction on the R¹-substituted N^C^N ligand, whereas oxidation likely occurs either on the Pt-phenylacetylide moiety and/or the cyclometalated ligand. In CH₂Cl₂ solution at room temperature, the complexes show phosphorescent emissions ranging from green to orange, depending on the R¹ and R² substituents on the ligands. In KBr solid state matrix, excluding complexes bearing a trifluoromethyl substituted ligand, all compounds exhibit red emission. The presence of an alkynyl ancillary ligand has limited influence on absorption and emission spectra except in the case of the complex with the strongly electron-donating diphenylamino R² substituent on the alkynyl ligand, for which a significant red-shift was observed. The alkynyl Pt(II) complex with OMe groups as both R¹ and R² substituents shows the best emission quantum yield (0.81 in CH₂Cl₂ solution) in this series. The full series of DFT calculated band gaps correlated generally well with the electrochemical and absorption data and reasonably model the impact of the substituents on the electronics of these complexes.