Synthesis And Photoelectric Properties Of Chiral Cyclometalated Platinum Complexes Bridged By Bis (Diphenylphosphine) Alkane

High-performance phosphorescent complexes have always been the research focus of novel luminescent materials.Cyclometalated Pt（II）complexes have received widespread attention due to their good planarity,high luminescence quantum efficiency,long phosphorescence lifetime,and large Stokes shift.When the bridging ligand is introduced to construct dinuclear Pt（II）complexes,an effective intramolecular Pt···Pt interaction can be formed,and the solution can emit high-efficiency phosphorescence at low concentrations.In addition,through the modification of the cyclometalated ligand and the selection of the bridging ligand,the intramolecular Pt···Pt,π-πand other interactions can be effectively controlled.A series of phosphorescent compounds with various luminescent colors can be obtained,which can be used in organic electroluminescent devices（OLEDs）,new probes,stimuli-response optical sensors and other fields.The introduction of chiral elements into cyclometalated Pt（II）complexes may also induce distorted coordination configurations around Pt（II）centers or helical stacked aggregates,bringing some interesting chiral optical properties.In this paper,chiral cyclometalated metal Pt（II）complexes Pt（C^N^N）Cl,Pt（N^C^N）Cl（C^N^N=6-benzene-2,2’-bipyridine,N^C^N=1,3-dipyridylbenzene）as the precursor.Through reacting precursors with bis（diphenylphosphine）alkane bridged ligand or triphenylphosphine monodentate ligand,we obtain a series of dinuclear and mononuclear platinum complexes with novel structure and enhanced chiral environment.Their crystal structures and spectral properties were studied.1.Solution properties of chiral C^N^N-type platinum complexes bridged by bis（diphenylphosphine）alkaneDistinct circularly polarized luminescence（CPL）activity was observed in chiral（C^N^N）Pt（II）[（C^N^N）=4,5-pinene-6′-phenyl-2,2′-bipyridine]complexes with bis-or triphenylphosphine ligands.Compared to the pseudo-square-planar geometry of chiral（C^N^N）Pt（II）complexes with chloride,phenylacetylene（PPV）and2,6-dimethylphenyl isocyanide（Dmpi）ligands,the coordination configuration around the Pt（II）nucleus of chiral（C^N^N）Pt（II）complexes with bulk phosphine ligands is far more distorted.The geometry is straightforwardly confirmed by X-ray crystallography.Upon varying the length of bridging ligand,intramolecular metal-metal interaction manipulation is accessible as evidenced from crystal structures.Complex（-）-1 exhibiting strong Pt···Pt interaction displays a red phosphorescence with maximum peak at 638 nm,while complex（-）-2 exhibiting weak Pt···Pt interaction displays a green phosphorescence with maximum peak at 530nm.The phosphines’participation enhanced the CPL signal of Pt（II）complexes profoundly,with the dissymmetry factor(g_lum)up to 10^-3.The distorted structures and enhanced chiroptical signals were further confirmed by time-dependent density functional theory（TD-DFT）calculations.2.Solid-state properties of chiral C^N^N-type platinum complexes induced by different bridging ligands and anionsCrystal structures of dinuclear cyclometalated Pt（II）complexes with different bridging bis（diphenylphosphino）alkane ligands and counter anions have been compared,and solid-state emissions of crystallite powders and PMMA films doped with luminescent Pt（II）complexes have been investigated.Interestingly,mechanochromic and vapochromic properties are exhibited for solids of dinuclear cyclometalated Pt（II）complex（-）-1 bridged by bis（diphenylphosphino）methane（dppm）,and multiple cycles have been repeated without any detectable degradation.However,no distinct stimuli-induced chromism can be observed with the naked eyes for solids of（-）-1 with other counter anions and PMMA films.In addition,with increasing the length of the bridging diphosphine ligand,green-solids without effective intramolecular Pt···Pt contacts have been obtained,and mechanochromic and vapochromic phenomena could not be detected.3.Spectral properties ofchiral N^C^N-type platinum complexesThree pairs of mononuclear platinum complexes 8-10 were synthesized through bis（diphenylphosphine）ethane,bis（diphenylphosphine）butane and triphenylphosphine ligands coordinating with pinene-modified chiral Pt（N^C^N）Cl complexes.Mass spectrometry and NMR showed that the bridging ligand did not bridge the two Pt（N^C^N）fragments,and only one Pt（N^C^N）Cl precursor reacted with the phosphine ligand.UV and emission spectra show that there is no intramolecular or intermolecular Pt···Pt interaction in complexes 8-10.These complexes all exhibited similar emission spectra with the mononuclear precursor Pt（N^C^N）Cl.Electronic circular dichroism（ECD）spectra show that the ECD spectra of compounds（-）-8 and（-）-9 and their enantiomers（+）-8 and（+）-9 are almost mirror-symmetrical.After the introduction of bis（diphenyl）phosphine or triphenylphosphine ligands,the emisssion lifetime of the compound changes slightly.