Energy transfer probability in organic electrophosphorescence device with dopant

Based on the energy transfer process from host to dopant in an organic electrophosphorescent （EP） device, the expression of energy transfer probability （η） between the host （TPD） and guest （Ir（ppy）3） EP systems was proposed. The results show that： （1） The rate of the triplet energy transfer （KHG and KGH） increases exponentially with increasing donor-acceptor molecular distance （R）, whereas decreases as the intermolecular distance （RHH） increases from 0.8 to 2.4 nm. Furthermore, KGH changes more quickly than KHG. （2） The energy transfer probability （η） increases as R reduces, and the RHH changes can be safely neglected for R〈0.9 nm. The situation changes for 0.9nm〈 R 〈 1.1nm, RHH （〈1nm） plays an essential role when η changes and increases with the latter. However, if R〉1.1nm, the transfer probability will be below zero. Here, the energy transfer principle may be less important, and the high electroluminescence （EL） quantum efficiency of phosphorescent system will be attributed to the direct electron-hole recombination in phosphorescent molecules. （3） The η will increase when the Forster radius （R0） increases or Gibb＇s energy decreases.

Synthesis and phosphorescent properties of two novel iridium (Ⅲ) complexes bearing bulky tert-butyl substituents

The synthesis and phosphorescence properties of two novel Ir(Ⅲ)complexes bearing tert-butyl substituents,bis(4-tert-butyl-2- phenylbenzothiozolato-N,C^(2′))iridium(Ⅲ)(acetylacetonate)[(tbt)_2Ir(acac)]and bis(4-tert-butyl-1-phenyl-1H-benzimidazolato- N,C^(2′))iridium(Ⅲ)(acetylacetonate)[(tpbi)_2Ir(acac)],are reported,their molecular structures are confirmed by^1H NMR,ESI-MS and elementary analysis.Photoluminescence(PL)studies revealed that they can emit strong green and orange phosphorescence in high quantum yields.Compared to their prototypes lacking of tert-butyl substituents,the two novel iridium(Ⅲ)complexes both have shorter lifetimes and improved or nearly similar PL quantum efficiencies,implying that the exciton quenching is inhibited effectively when molecular steric hindrance increases.The two chelates have great potential to be used as electrophosphorescent materials.

Synthesis and Characterization of Novel Orange-emitting Iridium(Ⅲ)Complexes with Diphenylquinoline Ligands Containing Fluorinated Substituent

Three new cyclometalated iridium（m） complexes based on ligands of diphenylquinoline with fluorinated subsfituents were prepared, and characterized by elemental analysis （EA）, ^1H NMR, and mass spectroscopy （MS）. The photophysical and electrophosphorescent properties of the complexes were briefly discussed.

Novel Iridium Complex with Carbazol-2-yl-β-diketone Derivative:Low-energy Excitation and Red Electrophosphorescent Devices

A novel iridium-complex,（BPPBI） 2 Ir（2-TFDBC）[BPPBI=2-（biphenyl-4-yl）-1-phenyl-1H-benzo[d]imidazole,2-TFDBC=1-（9-ethyl-9H-carbazol-2-yl）-4,4,4-trifluorobutane-1,3-dione],was synthesized,and its structure and component were confirmed by 1 H NMR and element analysis,respectively.UV-Vis absorption and photoluminescent（PL） spectra of（BPPBI） 2 Ir（2-TFDBC） in dichloromethane were investigated.The Ir-complex exhibited a long wavelength excitation of 470 nm,i.e.,low-energy excitation.So,it is a promising candidate for phosphorescent probe and PL material.（BPPBI） 2 Ir（2-TFDBC）-based electroluminescent devices,ITO/MoO 3（10 nm）/NPB（80 nm）/CBP：x（BPPBI） 2 Ir（2-TFDBC）（20 nm）/TPBi（45 nm）/LiF/Al,were fabricated,where x（%） was of 4% or 8% doping concentration（mass fraction）;ITO=indium tin oxides;NBP=N,N＇-bis-（1-naphthalenyl）-N,N＇-bis-phenyl-（1,1＇-biphenyl）4,4＇-diamine,CBP=4,4＇-bis（N-carbazolyl）-1,1＇-biphenyl,TPBi=1,3,5-tris（1-phenyl-1H-benzimidazol-2-yl）benzene.The devices showed a red emission of 620 nm.The maximum current efficiency and brightness were 1.7 cd/A and 4063 cd/m 2 for a device of 8%（mass fraction） doping level,respectively.The moderate luminous efficiency was due to the inadequate energy transfer from the host material to the guest material.

Molecular hosts for triplet emitters in organic light-emitting diodes and the corresponding working principle

This paper summarizes the mechanism and routes for excitation of triplet emitters in dopant emission based phosphorescent organic light-emitting diodes (PhOLEDs),providing a comprehensive overview of recent progress in molecular hosts for triplet emitters in PhOLEDs.Particularly,based on the nature of different hosts,e.g.,hole transporting,electron transporting or bipolar materials,in which the dopant emitters can be hosted to generate phosphorescence,the respective device performances are summarized and compared.Highlights are given to the relationships among the molecular structure,thermal stability,triplet energy,carrier mobility,molecular orbital energy level and their corresponding device performances.

Recent progress in functionalized electrophosphorescent iridium(Ⅲ) complexes

Iridium（Ⅲ） complexes are one of the most important electrophosphorescent dyes with tunable emissions in the range of visible and near infrared lights,high photoluminescence yields and short lifetimes for high-efficiency organic light-emitting diodes（OLED） with 100% exciton harvesting.This review summarizes the recent development of electroluminescent Ir^（3＋） complexes functionalized with host-featured carrier-transporting groups,with emphasis on correlations between functionalization,optoelectronic properties and device performance.According to the introducing approaches,the complexes were sorted with conjugated and aliphatic linkages,as well as the types of functional groups.The modification effect on physical properties and the state-of-the-art device performances were discussed.

Resonance hosts for high efficiency solution-processed blue and white electrophosphorescent devices

The exploration of high-performance solution-processible host materials for blue and white electrophosphorescent devices is a key and fundamental challenge in the ongoing development of organic semiconductors.Herein,two solution-processible resonance host materials with self-adaptive characteristics are delicately designed and constructed.Because of the dynamic tautomerization upon resonance variation,these smart hosts show self-adaptive and selectively enhanced charge carrier flux at high triplet energy levels.Conferred by the resonance molecules,solution-processed blue and white devices exhibit excellent maximum current efficiencies(CEs)of 29.8 and 57.3 cd A−1,and external quantum efficiencies(EQEs)up to 14.5%and 23.5%,respectively.Our works highlight the significant progress of the solution-processed phosphorescent organic light-emitting diodes(PhOLEDs)using resonance host molecules,potentially furnishing a leap forward in constructing advanced organic semiconductors for next-generation optoelectronic devices.