Enhanced deep-red emission in donor-acceptor molecular architecture:The role of ancillary acceptor of cyanophenyl

Organic solid-state luminescent materials with high-efficiency deep-red emission have attracted considerable interest in recent years.Constructing donor-acceptor(D-A) type molecules has been one of most commonly used strategies to achieve deep-red emission,but it is always difficult to achieve high photoluminescence(PL) quantum yield(η_(PL)) due to forbidden charge-transfer state.Herein,we report a new D-A type molecule 4-(7-(4-(diphenylamino)phenyl)-9-oxo-9 H-fluoren-2-yl)benzonitrile(TPAFOCN),deriving from donor-acceptor-donor(D-A-D) type 2,7-bis(4-(diphenylamino)phenyl)-9 Hfluoren-9-one(DTPA-FO) with a fluorescence maximum of 627 nm in solids.This molecular design enables a transformation of acceptor from fluorenone(FO) itself to 4-(9-oxo-9 H-fluoren-2-yl)benzonitrile(FOCN).Compared with DTPA-FO,the introduction of cyanophenyl not only shifts the emission of TPA-FOCN to deep red with a fluorescence maximum of 668 nm in solids,but also maintains the high η_(PL) of 10%.Additionally,a solution-processed non-doped organic light-emitting diode(OLED)was fabricated with TPA-FOCN as emitter.TPA-FOCN device showed a maximum luminous efficiency of0.13 cd/A and a maximum external quantum efficiency(EQE) of 0.22% with CIE coordinates of(0.64,0.35).This work provides a valuable strategy for the rational design of high-efficiency deep-red emission materials using cyanophenyl as an ancillary acceptor.     

Synthesis, characterization, and electroluminescent properties of star shaped donor-acceptor dendrimers with carbazole dendrons as peripheral branches and heterotriangulene as central core

Luminescent and redox-active heterotriangulene-based dendrimers (G1 and G2) of first and second generation have been synthesized, and their photophysical properties, oxidation behaviors, and applications in organic light emitting diodes (OLEDs) have been investigated. The dendrimers show efficient aggregation-induced emissions originated from the carbazole dendrons, heterotriangulene core, intramolecular charge-transfer (ICT), and intermolecular aggregation absorptions. Highest-occupied molecular orbital and lowest-unoccupied molecular orbital (HOMO and LUMO) values were acquired using UV-vis spectroscopy and cyclic voltammetry. The OLEDs fabricated with G1 and G2 as non-doping emitters exhibit exclusive aggregation-induced luminescence peaking at 600 and 630 nm, respectively, and demonstrate a good performance with maximum luminance of 1586 cd m⁻² at current efficiency of 5.3 cd A⁻¹ for G1 and 827 cd m⁻² at current efficiency of 6.9 cd A⁻¹ for G2.     

Molecular engineering on all ortho-linked carbazole/oxadiazole hybrids toward highly-efficient thermally activated delayed fluorescence materials in OLEDs

The highest efficiency thermally activated delayed fluorescence(TADF) emitters in OLEDs are mostly based on twisted donor/acceptor(D/A) type organic molecules.Herein,we report the rational molecular design on twisted all ortho-linked carbazole/oxadiazole(Cz/OXD) hybrids with tunable D-A interactions by adjusting the numbers of donor/acceptor units and electron-donating abilities.Singlet-triplet energy bandgaps(ΔE_(ST)) are facilely tuned from～0.4,0.15 to～0 eV in D-A,D-A-D to A-D-A type compounds.This variation correlates well with triplet-excited-state frontier orbital spatial separation efficiency.NonTADF feature with solid state photoluminescence quantum yield(PLQY)10% is observed in D-A type2 CzOXD and D-A-D type 4 CzOXD.Owing to the extremely low ΔE_(ST) for efficient reverse intersystem crossing,strong TADF with PLQY of 71%-92% is achieved in A-D-A type 4 CzDOXD and 4 tCzDOXD.High external quantum efficiency from 19.4% to 22.6% is achieved in A-D-A typed 4 CzDOXD and 4 tCzDOXD.     

Molecular engineering on all ortho-linked carbazole/oxadiazole hybrids toward highly-efficient thermally activated delayed fluorescence materials in OLEDs

All ortho-linked D-A and D-A-D molecules exhibit non-TADF feature due to broad spatial overlap at triplet excited state for large △E_ST,while A-D-A compounds show strong TADF property owing to efficient spatial separation for small △E_ST.     

Color tuning of iridium complexes for organic light-emitting diodes: The electronegative effect and π-conjugation effect

Novel red phosphorescent emitter bis(4-phenylquinazolinato-N,C^2′) iridium(acetylacetonate) [(pqz)₂Ir(acac)], bis(1-(1′-naphthyl)-5-methylisoquinolinato-N,C^2′)iridium(acetylacetonate) [(1-mniq)₂Ir(acac)] and bis(1-(2′-naphthyl)-5-methylisoquinolinato-N,C^2′)iridium(acetylacetonate) [(2-mniq)₂Ir(acac)] have been synthesized and fully characterized. The electronegative effect of (pqz)₂Ir(acac) ligand shows almost the same influence as the extended π-conjugation effect of (2-mniq)₂Ir(acac). Density functional theory (DFT) was applied to calculate the Kohn-Sham orbitals of HOMOs and LUMOs in the iridium complexes to illustrate the N(1) electronegative atom effect. Finally, lowest triplet state (T₁) energies calculated by time-dependent DFT (TDDFT) were compared with the experimental electroluminescent data. The calculated data for the iridium complexes agreed fairly well with experimental data. Electroluminescent devices with a configuration of ITO/NPB/CBP:dopant/BCP/AlQ₃/LiF/Al were fabricated. The device using (pqz)₂Ir(acac) as a dopant showed deep-red emission with 1931 CIE (Commission International de L’Eclairage) chromaticity coordinates x = 0.70, y = 0.30.     

Evolution of emission manners of organic light-emitting diodes: From emission of singlet exciton to emission of doublet exciton

The emission manners of organic light-emitting diodes(OLEDs) have experienced almost three-decade evolution.In this review,we briefly summarized the emission manners of OLEDs including:(ⅰ) emission from singlet exciton;(ⅱ) emission from triplet exciton;(ⅲ) emission from singlet exciton converted from triplet exciton.Then we introduced a new type of OLEDs with the emission from doublet exciton,wherein organic neutral radicals are used as emitters.Due to the spin-allowed transition of doublet excitons,using neutral radicals as emitters is believed to be a new way to break the 25%upper limit of internal quantum efficiency of OLEDs.The progress of emissive stable neutral radicals is also shortly reviewed.     

Enhanced self-host blue emission of CaSrSb2O7 materials via Bi3+ ion doping for high CRI WLEDs,security inks and flexible displays

Luminescent materials are indispensable in our daily lives and have already been widely applied in various fields. Herein, novel self-host blue-emitting CaSrSb₂O₇ and CaSrSb₂O₇:Bi³⁺ phosphors with orthorhombic space group Imma (74) were successfully prepared. The phase purity, elemental composition, morphology, luminescent behaviors, etc. were investigated in detail. To compare the luminescence properties of rare-earth-activated phosphors, the self-host blue-emitting CaSrSb₂O₇ phosphor with unique performance exhibited a good quantum yield (QY) of 39.81%, and its emission intensity and QY could also be improved by doping Bi³⁺ ions. The CaSrSb₂O₇:Bi³⁺ phosphor was located in the pure blue region with the Commission Internationale de I'Eclairage chromaticity coordinate of (0.151, 0.058) and good color purity of 89.35%. For identifying its potential applications, the packaged white light-emitting diode device emitted a high color rendering index value of 93.66 under a forward current of 300 mA, and it would be further applied in security inks and flexible displays owing to its strong emission by the naked eyes. These results suggest that novel self-host blue-emitting CaSrSb₂O₇:Bi³⁺ phosphors could be used in multifunctional applications.     

The driving force for solute retention in electron donor-acceptor chromatography: Electrostatic versus charge-transfer interactions

Summary Charge-transfer interactions are often assumed to be dominant among the noncovalent interactions that govern the solute retention in electron donor-acceptor chromatography. This popular view, however, has been called into question by recent studies that suggest an important role for electrostatic interactions in the formation of donor-acceptor complexes. We reported here an experimental investigation concerning the question as to whether charge-transfer or electrostatic interactions are the driving force for solute retention in donor-acceptor chromatography. Using three chromatographic systems composed of a dinitrobenzene derived stationary phase and a hexane based mobile phase, we determined retention factors for a range of aliphatic and aromatic hydrocarbons and correlated them with molecular properties that describe the solute's dispersion, charge-transfer, and electrostatic characteristics. It was found that the molecular polarizability and ionization potential give either very poor or no correlation with solute retention whereas the molecular quadrupole moment is a linear function of the logarithmic retention factor. These results were interpreted as showing that electrostatic, rather than charge-transfer or dispersion, interactions play a major role in determining solute retention. The dominance of the electrostatic interactions over the other noncovalent interactions was discussed in terms of distance dependency of the interaction energy. Dedicated to Professor John H. Knox on the occasion of his 70th birthday.     

金属纳米粒子增强有机光电器件性能研究进展

金属纳米粒子以其特殊的体积效应、量子尺寸效应、表面效应和宏观量子隧道效应提供了诸多优异的光学和电学性能.实验表明,利用金属纳米粒子的光学和电学效应可以有效提升有机光电器件的综合性能.目前在有机发光二极管器件中流明效率最好的增强效果为150%,在有机光伏器件中功率转换效率最好的增强效果为70%,特别是在一些高效有机光电器件中的成功应用,虽然增强的比例相对较低,但是器件效率基数大,最终得到的器件性能相当优异.这些性能提升的主要机理包括表面增强荧光、等离激元光捕获、能量转移、电学效应、散射效应等.本文以金属纳米粒子的表面等离子体共振效应和电学效应为主线,按照不同纳米粒子及器件中的修饰位置进行分类,系统总结了金属纳米粒子提高有机发光二极管器件和有机光伏器件性能方面的工作.针对纳米粒子的局域表面等离子共振效应作用范围小,增强波长单一等问题,总结了一些新的设计思路如远场增强效应、纳米粒子和激子剖面的调控与匹配及散射增强效应等,希望为进一步的结构设计提供帮助.     

Synthesis and characterization of fluorene and carbazole dithienosilole derivatives for potential applications in organic light-emitting diodes

Several fluorene or carbazole-based dithienosiloles (DTSs) have been synthesized and their thermal, photophysical, and electrochemical properties have been systematically investigated. These compounds show high thermal stability with glass transition temperature above 110 °C as well as decomposition temperatures at ∼400 °C. Intense green emission is observed in the spectral region of 500-510 nm for all compounds (Φ_PL=0.31-0.80), that is, attributed to both the 5,5′-substituents of the DTS ring and DTS-based π-π^∗ transition. Based on the emission spectra at 77 K, the triplet energy for these compounds was calculated to be within 2.1-2.2 eV, indicating that they may be used as host materials for red emitters in organic light-emitting diodes (OLEDs). All compounds exhibit reversible oxidation and possess low-lying LUMO energies, owing to the conjugated fluorene/carbazole substituents on the DTS. This along with the high thermal/electrochemical stabilities and high fluorescent quantum efficiencies makes the new DTSs compounds promising candidates for use in OLEDs as emitters, host and electron-transporting materials.     

The impact of molecular emission in compositional depth profiling using Glow Discharge-Optical Emission Spectroscopy

The scope of this paper is to investigate and discuss how molecular emission can affect elemental analysis in glow discharge optical emission (GD-OES), particularly in compositional depth profiling (CDP) applications. Older work on molecular emission in glow discharges is briefly reviewed, and the nature of molecular emission spectra described. Work on the influence of hydrogen in the plasma, in particular elevated background due to a continuum spectrum, is discussed. More recent work from sputtering of polymers and other materials with a large content of light elements in a Grimm type source is reviewed, where substantial emission has been observed from several light diatomic molecules (CO, CH, OH, NH, C₂). It is discussed how the elevated backgrounds from such molecular emission can lead to significant analytical errors in the form of “false” depth profile signals of several atomic analytical lines. Results from a recent investigation of molecular emission spectra from mixed gases in a Grimm type glow discharge are presented. An important observation is that dissociation and subsequent recombination processes occur, leading to formation of molecular species not present in the original plasma gas. Experimental work on depth profiling of a polymer coating and a thin silicate film, using a spectrometer equipped with channels for molecular emission lines, is presented. The results confirm that molecular emission gives rise to apparent depth profiles of elements not present in the sample. The possibilities to make adequate corrections for such molecular emission in CDP of organic coatings and very thin films are discussed.     

Bimolecular nature of boron trifluoride catalyzed glycosylation of a galactosyl donor: The role of the acceptor

Density functional theory (DFT) computations disclose the mechanism of a crucial neighboring participation step in BF₃ catalyzed stereoselective glycosylation of 1,2‐cyclopropaneacetylated galactosyl donor. Two tandem S_N2 displacements comprise this step: first, the glycosyl acceptor attacks the BF₃‐activated donor to break the donor's 1,2‐cyclopropane ring; then, the donor's 2‐acetyl oxygen substitutes the acceptor to accomplish the neighboring participation. A donor–acceptor hydrogen bond has been found to lower the overall activation free energy. This mechanism is preferred over a 2‐acetyl oxygen coface S_N2 displacement mechanism, in which no glycosyl acceptor is involved. © 2013 Wiley Periodicals, Inc.     

The strength and length of donor-acceptor bonds in molecular complexes

Numerous published data on the structure and thermodynamics of formation of molecular complexes are analyzed. The enthalpies of complexation (−ΔH) are related to the characteristic parameter Δr = [r _DA−a ₁(r _D+r _A)], where r _DA is the donor-acceptor bond length determined by microwave spectroscopy and X-ray analysis, r _D and r _A are the tabulated values of the homopolar covalent radii of the heteroatoms that form the donor-acceptor bond, and a ₁ is an empirical coefficient equal to 0.901±0.007. The relation between −ΔH and Δr values has the form −ΔH = a ₂/Δr (a ₂ = 21.6±1.6 kJ Å mol⁻¹), with a mean relative error of approximation of about 15% and a correlation coefficient of 0.97. As the strength of the complex increases, the donor-acceptor bond length approaches the sum of the heteropolar covalent radii of the atoms involved in the bond (Δr tends to zero). At Δr ≫ 1, the strength of complexes is determined by weak van der Waals interactions between the complex components and the −ΔH values tend to zero. Dedicated to the memory of E. N. Guryanova (1911–2004), a prominent scientist who formulated the basic principles elaborated by her disciples in this review. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1869–1878, October, 2007.     

Enhanced activity of α-chymotrypsin in organic media using designed molecular staples

We report the enhancement of α-chymotrypsin activity in organic solvents using modified peptides bearing two crown ethers. The transesterification of N-acetyl-l-phenylalanine ethyl ester with 1-propanol was used as model reaction. Co-lyophilization of crown ether modified peptides with α-chymotrypsin prior to use resulted in an increase of enzyme catalytic activity in non-aqueous media. The efficiency of enzyme activation is dependent on the amino acid sequence of peptidic additives and on the positions of the amino acids bearing the crown ligand.     

New applications of poly(arylene ether)s in organic light-emitting diodes

Compared with conventional π-conjugated polymers,poly(arylene ether)s(PAEs) may take advantages of excellent thermal properties,well-defined effective conjugated length and no catalyst contamination.Recently,their applications have been extended from engineering plastics to optoelectronic materials.In this review,various kinds of functional PAEs used as fluorescent polymers,host polymers and phosphorescent polymers in organic light-emitting diodes(OLEDs) are outlined,and their molecular design,synthesis and device performance are overviewed.     

Towards deep‐blue phosphorescence: molecular design and property prediction of iridium complexes with pyridinylphosphinate ancillary ligand

A series of iridium complexes ( 1 – 5 ), which consist of two 2‐(2,4‐difluorophenyl)pyridine (dfppy)‐based primary ligands and one pyridinylphosphinate ancillary ligand, have been investigated theoretically for screening highly efficient deep‐blue light‐emitting materials. Compared with the reported dfppy‐based emitter 1 , the designed iridium complexes 3 – 5 with the introduction of a stronger electron‐withdrawing (–CN, –CF₃ , or o‐carborane) group and a bulky electron‐donating (tert‐butyl) group in dfppy ligands can be achieved to display the emission peaks at 443, 442, and 447 nm, respectively. The electronic structures, absorption and emission properties, radiative and nonradiative processes of their excited states, and charge injection and transport properties of the iridium complexes are analyzed in detail. The calculated results show that designed iridium complexes have comparable radiative and nonradiative rate constants with 1 , and are expected to have similar quantum efficiency with 1 . Meanwhile, these designed complexes keep the advantages of the charge transport properties of 1 , indicating that they are potential iridium complexes for efficient deep‐blue phosphorescence. This work provides more in‐depth understanding the structure–property relationship of dfppy‐based iridium complexes, and shed lights on molecular design for deep‐blue phosphorescent metal complexes.     

有机玻璃雕刻过程中有害气体的3阶段预浓缩GC/MS分析

研究了3阶段预浓缩气相色谱-质谱法检测有机玻璃在雕刻过程中排放的有害气体的组成。研究结果表明,气体中含有12种以上的有机污染物。其中甲基丙烯酸甲酯、丙烯酸甲酯、苯、甲苯、苯乙烯等5种有毒有害物可以作为代表该行业特征的污染物加以监控。     

聚集诱导发光分子的光电功能与器件应用

光电功能分子通常以薄膜和聚集体的形式显示功能, 聚集诱导发光（AIE）分子体系的发现为解决固态下聚集诱导荧光猝灭（ACQ）难题提供了新的思路. 本文总结了近年来本课题组发展的一系列AIE 分子, 侧重介绍这些AIE 分子的光电功能与器件应用, 特别是在有机电致发光器件和有机激光方面的应用. AIE 材料显示非常高的电致发光效率, 在显示与白光器件方面潜力巨大. 在发展电泵有机激光方面, AIE 材料特点突出, 是最有前景的一类材料.     

Influence of donor:acceptor ratio on charge transfer dynamics in non-fullerene organic bulk heterojunctions

The donor:acceptor(D:A) blend ratio plays a very important role in affecting the progress of charge transfer and energy transfer in bulk heterojunction(BHJ) orga nic solar cells(OSCs).The proper D:A blend ratio can provide maximized D/A interfacial area for exciton dissociation and appro p riate domain size of the exciton diffusion length,which is beneficial to obtain high-performance OSCs.Here,we comprehensively investigated the relationship between various D:A blend ratios and the charge transfer and energy transfer mechanisms in OSCs based on PBDB-T and non-fullerene acceptor IT-M.Based on various D:A blend ratios,it was found that the ratio of components is a key factor to suppress the formation of triplet states and recombination energy losses.Rational D:A blend ratios can provide appropriate donor/accepter surface for charge transfer which has been powerfully verified by various detailed experimental results from the time-resolved fluorescence measurement and transient absorption(TA) spectroscopy.Optimized coherence length and crystallinity are verified by grazing incident wide-angle X-ray scattering(GIWAXS) measurements.The results are bene ficial to comprehend the effects of various D:A blend ratios on charge transfer and energy transfer dynamics and provides constructive suggestions for rationally designing new materials and feedback for photovoltaic performance optimization in non-fullerene OSCs.