Theoretical Investigation Of Highly Efficient Phosphorescent Materials Based On Platinum(Ⅱ) Complexes

Density Functional Theory（DFT）and Time-dependent Density Functional Theory（TDDFT）were carried out to gain insights into a series of transitional-metal Pt（Ⅱ）complexes.At the study’s start,we explored the influence of the introducing five–six‐membered metallacyclegeometries and linking a substituent（such as phenyl）at bridge atoms on electron strctures and photophysics properties,and concluded the incorporation of appropriate introction can achieved fine emission color tuning and high phosphorescence quantum yield of phosphorescentcomplexes.phosphorescent properties of these complexes show a clear dependence on the electronegativity of bridge atoms.Subsequently,we were attracted by the unique structure of the bis（o-carboborane）ligands,we elucidate the relationship between the structures and properties of complexes with different binding modes and theincremental number of carboranes.Based on our analysis,a series of complexes aredesigned through introducing different substituents at B（12）position to tune the phosphorescent properties of these complexes,which reveals a potentially new avenue for the design of novelPTMCs in OLEDs.However,the contribution of carborane to molecular orbital is still small enough to be ignored,which means that the carborane has little effect on the electronic structure of the complexes,and it is still a non-functional ligand.At the end of investigation,we find that dtb-bpy ligand play a vital role inemissive properties,especially the electronic structures.So we propose a conjecture:can we improve the contribution of carborane on molecular orbitals by regulating dtb-bpy ligands?Therefore,we change the structure of the ligand by interrupting or increasing conjugated chain,so as to regulate its phosphorescent property and make it a more efficient phosphorescent material.Hence,this work successfully illustrated the structure-property relationship and provide valuable information to design highly efficient phosphorescent material.This study mainly contains three aspects as follow:1.Electronic structures and photophysical properties of phosphorescent platinum（Ⅱ）complexes with tridentate C^N*N cyclometalated ligandsTo get an insight into the structure–property relationships in a series of strongly phosphorescent platinum（Ⅱ）complexes with tridentate C^N*N cyclometalated ligands,their electronic structures and electroluminescence properties were systematically investigated via density functional theory and time‐dependent density functional theory.Moreover,the factors related to the radiative and non‐radiative decay process,including the transition electric dipole moment?₅),the energy difference between singlet and lowest triplet excited statesΔE（S_n–T₁）and the spin–orbital coupling matrix elements?₉)|?|₁?,as well as the energy gap between T₁ and S₀ statesΔE（T₁–S₀）and absorption–emission Stokes shifts have been calculated.Fine emission color tuning and high phosphorescence quantum yield of phosphorescent complexes may be achieved through introducing five–six‐membered metallacycle geometries and linking a substituent（such as phenyl）at bridge atoms.Additionally,phosphorescent properties of these complexes show a clear dependence on the electronegativity of bridge atoms.2.Revealing the unique properties of platinum（Ⅱ）complexes with bidentate bis（o-carborane）ligandsThe phosphorescent transition-metal complexes（PTMCs）with bidentate 1,1’-bis（o-carborane）（bc）ligand are theoretically studied for the first time.The DFT（density functional theory）and TD-DFT（time-dependent density functional theory）are utilized to elucidate the relationship between the structures and properties of complexes with different binding modes and the incremental number of carboranes.Compared with previous common bidentate ligands,the introduction of bulky carboranes enormously changes the electronic structures,electroluminescence properties（including phosphorescent emission band,radiative and nonradiativedecay processes）and intermolecular interactions of complexes.While the variousbinding modes between bc ligand and metal center only influence the degree of structuraldistortion and the intermolecular interaction.Based on our analysis,a series of complexes aredesigned through introducing different substituents at B（12）position to tune the phosphorescent properties of these complexes,which reveals a potentially new avenue for the design of novel PTMCs in OLEDs.3.Fine tuning the functional ligand of complex Pt（Et-bc）（dtb-bpy）to regulate its phosphorescent propertyThough the previous investigation,we found that the contribution of bidentate 1,1’-bis（o-carborane）（bc）ligand to molecular orbital is still small enough to be ignored,which means that the carborane has little effect on the electronic structure of the complexes.But the dtb-bpy ligand plays a vital role in emissive properties,especially the electronic structures.So we change the structure of the dtb-bpy ligand by interrupting its conjugated chain or increasing its conjugation,so as to regulate its phosphorescent property and make it a more efficient phosphorescent material.Disrupting and extending the conjugate chains are common methods of regulating ligands to improve molecular properties,which is better?What are the advantages and disadvantages of each other?Density Functional Theory（DFT）and Time-dependent Density Functional Theory（TDDFT）were carried out to gain insights into the photophysical property of these complexes and provide valuable information to design highly efficient Pt（Ⅱ）complexes.