Theoretical Investigation Of Highly Efficient Blue Phosphorescent Materials Based On Platinum(?) And Iridium(?) 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)and Ir(III)complexes.At the study's start,we have introduced several typical substituents,especially o-carborane and fluorinated aromatic sulfonyl groups,as well as explored the influence of these subtituents on electron strctures and photophysics properties and concluded the incorporation of appropriate substituents can obtain highly-efficient bule-emitting OLED materials.Later,we have observed that besides introducing subtituents,we can also obtain highly-efficient bule-emitting OLED materials through modifing the coordinated ligand.In the end,we found not only electron-withdrawing capability but also the conjugative effect have significant influence on electron strctures and photophysics properties.As revealed,the stronger electron-withdrawing capability and smaller conjugative effect may give rise to blue-shifted emission behavior and larger radiative decay rate constants as well as faster nonradiative decay process.These findings successfully illustrated the structure-property relationship and provide valuable information to design highly efficient phosphorescent material.This study mainly contains four aspects as follow: 1.The Electronic Structures and Photophysical Properties of Platinum Complexes with C?N?N Ligands: Influence of Carborane SubstituentCarboranes has attracted increasing interest in the scientific community due to their remarkable structures and strong electron-withdrawing abilities.In this article,four platinum complexes: [(C?N?N)PtC?CPh](1),[(C?N?N)PtC?C-TPA](2),[(C?N?N)PtC?C-TAB](3),[(C?N?N)PtC?C-CB](4),(where TPA= triphenylamine,TAB= triarylboryl,CB= o-carborane),have been calculated via the density functional theory(DFT)and the time-dependent density functional theory(TDDFT)methods to mainly explore the influence of carborane subtituents on electron strctures,photophysics properties and radiative decay processes.The calculated results reveal that 2 with electron-donating triphenylamine has a low radiative decay rate constant and a red-shifted emission band,but 3 and 4 containing electron-withdrawing triarylboryl and o-carborane exhibit the opposite properties,especially 4,supposed to have the highest phosphorescence quantum yield with the smallest nonradiative decay rate constant.These findings successfully illustrated the structure-property relationship and the designed complexe 4 with carborane can server as the highly efficient phosphorescent material in the future.2.Theoretical Investigation and Design of Highly Efficient Blue Phosphorescent Iridium(III)Complexes Bearing Fluorinated Aromatic Sulfonyl GroupsIn this article,the influence of fluorinated aromatic sulfonyl unit on electronic structures and photophysical properties of a series of heteroleptic functional Ir(III)complexes was elaborated via density functional theory(DFT)and time-dependent density functional theory(TDDFT)methods.To further explore quantum yields of these complexes,the factors which determine the radiative processes,including transition dipole moments ?(Sn),singlet-triplet splitting energies ?E(Sn–T1),and SOC matrix elements?T1| HSOC| Sn?were calculated.In addition,the SOC matrix elements between the lowest triplet state and the ground state,absorption-emission Stokes shifts as well as energy gaps between T1 and S0 states were also computed to describe the non-radiative decay processes.As demonstrated by the results,complex 4,introducing fluorinated phenylsulfonyl units into 5-position of the phenyl ring of all three C^N ligands,has larger radiative decay rate constant and the smallest non-radiative decay rate constant among these complexes,as well as exhibits significant blue-shifted behaviour and emits in blue region,which is considered to be a highly-efficient blue-emitting emitter applied in OLED.These findings successfully illustrated the structure–property relationship and provided valuable information for developing highly efficient blue-emitting phosphors in the future.3.Fine tuning Phosphorescent Properties of Platinum Complexes via Different N-heterocyclic-based C^N^N LigandsIn this article,series of platinum(II)complexes with different [C^N^N] cyclometalated ligand scaffolds was elaborated via density functional theory(DFT)and time-dependent density functional theory(TDDFT)methods to mainly explore how the N atomic number,the atomic number of cyclization and the position of N atom influence phosphorescent processes(radiative and nonradiative decay processes).Thereinto,the factors which determine the radiative processes,including ?(Sn)for S0–Sn transitions,?E(Sn–T1)and SOC matrix elements?T1| HSOC| Sn?were calculated.In addition,according to the energy gap law,the absorption-emission Stokes shifts as well as energy gaps between T1 and S0 states were also computed to describe the nonradiative decay processes qualitatively.As revealed,compared with six-membered N-heterocyclic compounds,five-membered N-heterocyclic compounds exhibit obvious blue-shifted behaviors,smaller nonradiative decay rate constants and similar radiative decay rate constant,especially complex 2b with the other N atom at the 4-position of five-membered N-heterocyclic ligand,which leads to a maximum hypsochromic shift of phosphorescence band and relatively larger radiative decay rate constant and smaller nonradiative decay rate constant among these complexes.These findings successfully illustrated the structure–property relationship and provide valuable information to design highly efficient phosphorescent material.4.Theoretical study on influence of both electron-withdrawing capability and conjugative effect of electron-withdrawing substituents introduced on phosphorescent properties of platinum(II)complexesIn this report,to explore how the electron-withdrawing capability and the conjugative effect of substituents combine to influence the electronic structures and phosphorescent properties,six platinum complexes bearing different electron-withdrawing groups have been calculated via density functional theory(DFT)and time-dependent density functional theory(TDDFT)methods.Thereinto,the factors which determine the radiative processes,including ?(Sn)for S0-Sn transitions,?E(Sn–T1)and the spin-orbit coupling(SOC)matrix elements?T1| HSOC| Sn?were calculated.And the energy gaps between T1 and S0 states,Huang-Rhys factors and the SOC matrix elements?T1| HSOC| S0?were also computed to estimate the non-radiative decay processes.As a result,while introducing strong electron-withdrawing groups into phosphorescent transition-metal complexes,besides inductive effect(the electron-withdrawing capability),the conjugative effect of substituents also has significant impacts on phosphorescent properties and some regularity can be received.The stronger electron-withdrawing capability and smaller conjugative effect may give rise to blue-shifted emission behavior and larger radiative decay rate constants as well as faster nonradiative decay process.Therefore,it is necessary to grasp the regularity and select appropriate electron-withdrawing groups for obtaining highly-efficient deep-bule-emitting materials in OLEDs.