Highly Efficient Greenish-Yellow Phosphorescent Organic Light-Emitting Diodes Based on a Novel 2,3-Diphenylimidazo[1,2-a]Pyridine Iridium(Ⅲ) Complex

A cyclometalated greenish-yellow emitter 2,3-diphenylimidazo[1,2-a]pyridine iridium（Ill） complex is successfully synthesized and used to fabricate phosphorescent organic light-emitting diodes. The optimized device exhibits a greenish-yellow emission with the peak at 523nm and a strong shoulder at 557nm, corresponding to Commission Internationale de l＇Eclairage coordinates of （0.38, 0.68）. The full width at half maximum of the device is 93 nm, which is broader than the fac-tris（2-phenylpyridine）iridium [Ir（ppy）3] based reference device of 78 nm. Meanwhile, a maximum current efficiency of 62.6 cd/A （47.51m/W） is obtained. This result is higher than a maximum current efficiency of 54.8 cd/A （431m/W） of the Ir（ppy）a based device. The results indicate that this new iridium complex may have potential applications in fabricating high color rendering index white organic light emitting diodes.

Highly efficient polymer phosphorescent light-emitting devices based on a new polyfluorene derivative as host

Several highly efficient iridium-complex polymer light-emitting devices （PLEDs） are fabricated, with a newly synthesized blue conjugated polymer, poly[（9,9-bis（4-（2-ethylhexyloxy）phenyl）-fluorene）-co-（3,7-dibenziothiene-S,S- dioxide15）] （PPF-3,TSO15）, chosen as host. High luminous efficiencies of 7.4 cd.A-1 and 27.4 cd.A-1 are achieved in red and green PLEDs, respectively, by optimizing the doping concentrations of red phosphorescent dye iridium bis（1- phenylisoquinoline） （acetylacetonate） （Ir（piq）） and green phosphorescent dye iridium tris（2-（4-tolyl）pyridinato-N, C2＇） （Ir（mppy）3）.Furthermore, highly efficient white PLEDs （WPLEDs） with the Commission Internationale de l＇Eclairage （CIE） coordinates of （0.35, 0.38） are successfully produced by carefully controlling the doping concentration of the irid- ium complex. The obtained WPLEDs show maximal efficiencies of 14.4 cd.A-1 and 10.1 lm.W-1, which are comparable to those of incandescent bulbs. Moreover, the electroluminescent spectrum of the white device with an initial luminance of about 1000 cd.m-2 is stable, subject to constant applied current stress, indicating that good device stability can be obtained in this system.

Enhancement of electroluminescent properties of organic optoelectronic integrated device by doping phosphorescent dye

Organic optoelectronic integrated devices（OIDs） with ultraviolet（UV） photodetectivity and different color emitting were constructed by using a thermally activated delayed fluorescence（TADF） material 4, 5-bis（carbazol-9-yl）-1, 2-dicyanobenzene（2 CzPN） as host. The OIDs doping with typical red phosphorescent dye [tris（1-phenylisoquinoline）iridium（Ⅲ）, Ir（piq）3], orange phosphorescent dye {bis[2-（4-tertbutylphenyl）benzothiazolato-N,C-（2＇）]iridium（acetylacetonate）,（tbt）2 Ir（acac）}, and blue phosphorescent dye [bis（2, 4-di-fluorophenylpyridinato）-tetrakis（1-pyrazolyl）borate iridium（Ⅲ）, FIr6] were investigated and compared. The（tbt）2 Ir（acac）-doped orange device showed better performance than those of red and blue devices, which was ascribed to more effective energy transfer. Meanwhile, at a low dopant concentration of 3 wt.%, the（tbt）2 Ir（acac）-doped OIDs showed the maximum luminance, current efficiency, power efficiency of 70786 cd/m^2, 39.55 cd/A, and 23.92 lm/W, respectively, and a decent detectivity of 1.07 × 10^11 Jones at a bias of -2 V under the UV-350 nm illumination. This work may arouse widespread interest in constructing high efficiency and luminance OIDs based on doping phosphorescent dye.

A Mixed Host Emitting Interlayer Based on CBP:TPBi in Green Phosphorescent Organic Light-Emitting Diodes

A series of green phosphorescent organic light-emitting diodes based on bipolar-transporting material 4,4Lbis- （carbazol-9-yl） biphenyl （CBP） are prepared. We insert a mixed host emitting interlayer （CBPx： electron- transporting material 1,3,＆tris （N-phenylbenzimidazole-2yl） （TPBi）1-X） in the middle of the emitting layer, and the best performance appears when x is 2/3. The position of this interlayer can also affect the performanee of phosphorescent organic light-emitting diodes. When this interlayer is close to the side of the electron transporting layer, the maximum value of luminance, the current efficiency and the power efficiency are 34090cd/m2 at 12 V, 60. 6 cd/A and 56.6 lm/W, respectively.

High-Efficiency Green Phosphorescent Organic Light-Emitting Diode Based on Simplified Device Structures

A high-efficiency green phosphorescent organic light emitting diode with a simplified structure is achieved that is free of a hole transport layer. The design of this kind of device structure not only saves the consumption of organic materials but also greatly reduces the structural heterogeneities and effectively facilitates the charge injection into the emissive layer. The resulting green phosphorescent organic light-emitting diodes （PHOLEDs） exhibit higher electroluminescent efficiency. The maximum external quantum efficiency and current efficiency reach 23.7% and 88 cd/A, respectively. Moreover the device demonstrates satisfactory stability, keeping 23.7% and 88cd/A, 22% and 82cd/A, respectively, at a luminance of 100 and 1000cd/m2. The working mechanism for achieving high efficiency based on such a simple device structure is discussed correspondingly. The improved charge carrier injection and transport balance are proved to prominently contribute to achieve the high efficiency and great stability at high luminance in the green PHOLEDs.

Platinum complexes as phosphorescent emitters in highly efficient organic light-emitting diodes

Applications of platinum complexes as phosphorescent emitters in high efficiency organic light-emitting diodes （OLEDs） were shortly discussed in this paper. Key recent studies on highly efficient blue, green, red and white-phosphorescent OLEDs based on Pt complexes are presented in terms of efficiency and color quality.

High Efficiency Blue Phosphorescent Organic Lighting-emitting Diodes with Novel Anode Structure

High-efficiency blue electrophosphorescent organic light-emitting devices employing MoO3 used as hole injection layer （HIL） and MoO3 doped N,N-dicarbazoly-3,5-benzene （mCP） as hole transport layer （HTL） were demonstrated. The blue OLED with the novel anode structure and TAPC used as electron blocking layer show a low turn-on voltage of 2.4 V, a maximum power efficiency of 33.6 lm/W at 3.1 V and 25 lrn/W with 1 000 cd/m2 at 3.8 V. It is also found that the efficiency of the devices is dependent on the different EBL materials. This is may because of relationship with the charge mobility and the triplet energy level of EBL materials. The device efficiency is determined by the charge balance which plays an important role.

Spectral Characteristics of White Organic Light-emitting Diodes Based on Novel Phosphorescent Sensitizer

White organic light-emitting diodes were fabricated by using a novel phosphorescence bis（1,2-diphenyl-1H-benzoimidazole）iridium（acetylacetonate）[（pbi）2Ir（acac）] as sensitizer and a fluorescent dye of 4- （dicyanomethylene）-2-t-butyl-6-（1,1,7,7-tetramethyljulolidyl-9-enyl）-4H-pyran （DCJTB） codoped into a carbazole polymer of poly（N-vinylcarbazole） （PVK）. Through characterizing the UV-Vis absorption spectra, the photoluminescence spectra of （pbi）2Ir（acac） and DCJTB, and the electroluminescence spectral properties of the WOLEDs, the energy transfer mechanisms of the codoped polymer system were deduced. The results demonstrate that the luminescent spectra with different intensity of （pbi）2Ir（acac） and DCJTB were co-existent in the EL spectra of the blended system, which is ascribed to an incomplete energy transfer process in the EL process. The efficient Forster and Dexter energy transfer between the host and the guests enabled a strong yellow emission from （pbi）2Ir（acac） and DCJTB, where （pbi）2Ir（acac） plays an important role as a phosphorescent sensitizer for DCJTB. With the blue emitting-layer of N,N＇-diphenyl-N,N＇-bis（1- naphthyl）（1,1＇-biphenyl）-4,4＇-diamine, the codoped system device achieved white emission. The codoped system showed that its Commissions Internationale de 1＇Eclairage coordinates were more independent of the variation of bias voltage than those of phosphorescent doped PVK systems.

Phosphorescent Cationic Iridium（Ⅲ） Complexes with 1,3,4-Oxadiazole Cyclometalating Ligands： Solvent-Dependent Excited-State Dynamics

To elucidate the nature of low-lying triplet states and the effect of ligand modifica- tions on the excited-state properties of functional cationic iridium complexes, the solvent- dependent excited-state dynamics of two phosphorescent cationic iridium（Ⅲ） complexes, namely [Ir（dph-oxd）2（bpy）]PF6 （1） and [Ir（dph-oxd）2（pzpy）]Pf6 （2）, were investigated by femtosecond and nanosecond transient absorption spectroscopy. Upon photoexcitation to the metal-to-ligand charge-transfer （MLCT） states, the excited-state dynamics shows a rapid process （τ-=0.7-3 ps） for the formation of solvent stabilized 3MLCT states, which significantly depends on the solvent polarity for both 1 and 2. Sequentially, a relatively slow process assigned to the vibrational cooling/geometrical relaxation and a long-lived phospho- rescent emissive state is identified. Due to the different excited-state electronic structures regulated by ancillary ligands, the solvation-induced stabilization of the 3MLCT state in 1 is faster than that in 2. The present results provide a better sight of excited-state relaxation dynamics of ligand-related iridium（Ⅲ） complexes and solvation effects on triplet manifolds.

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.

High-efficiency organic light-emitting diodes based on ultrathin blue phosphorescent modification layer

Yellow organic light-emitting devices （YOLEDs） with a novel structure of ITO/MoO3（5 nm）/NPB（40 nm）/ TCTA（15 nm）/CBP：（tbt）zIr（acac）（x%）（25 nm）/FIrpic（y nm）/TPBi（35 nm）/Mg：Ag are fabricated. The ultrathin blue phosphorescent bis[（4,6-difluorophenyl）-pyridi-nato-N,C2＇]（picolinate） iridium （III） （FIrpic） layer is regarded as a high- performance modification layer. By adjusting the thickness of FIrpic and the concentration of （tbt）2Ir（acac）, a YOLED achieves a high luminance of 41618 cd/m2, power efficiency of 49.7 lm/W, current efficiency of 67.3 cd/A, external quan- tum efficiency （EQE） of 18%, and a low efficiency roll-off at high luminance. The results show that phosphorescent material of FIrpic plays a significant role in improving YOLED performance. The ultrathin FIrpic modification layer blocks excitons in EML. In the meantime, the high triplet energy of FIrpic （2.75 eV） alleviates the exciton energy transport from EML to FIrpic.

Synthesis and Photoluminescence of a New Red PhosphorescentIridium(III) Quinoxaline Complex

A new cyclometalated iridium(III) complex with the formula [Ir(DPQ)2(acac)] (DPQ= 2,3-diphenylquinoxaline; acac=acetylacetone) was prepared. The structure of the complex was confirmed by Elemental Analysis (EA), 1H NMR, and mass spectroscopy (MS). The UV-vis absorption and photoluminescent properties of the complex were investigated.

Intracellular oxygen:Similar results from two methods of measurement using phosphorescent nanoparticles

The ability to resolve the spatio-temporal complexity of intracelular O_(2) distribution is the“HolyGrail” of cellular physiology.In an effort to obtain a minimally invasive approach to the mappingof intracllar O,tensions,two methods of phosphorescent lifetime imaging microscopy werecompared in the current study and gave similar results.These were two-photon confocal laserscanning microscopy with pinhole shifting,and picosecond time-resolved epi-phosphorescencemicroscopy using a single 0.5μm focused spot.Both methods utilized Ru coordination complexembedded nanopartidles(45 nm diameter)as the phosphorescent probe,excited using pulsedoutputs of a titanium sapphire Tsunami lasers(710-1050 nm).

The Current Progress and Challenges of Carbonized Polymer Dot-Based Room-Temperature Phosphorescent Materials

Carbonized polymer dots(CPDs)as one type of carbon dots have attracted widespread attention in recent years.The proposal of the“shell–core”structure of CPDs leads to further thinking about the association between their special structures and luminescent properties.In recent years,great progress has been made in the field of CPD-based room-temperature phosphorescent materials.This review pays particular attention to how the special“core–shell”structure of CPDs influences the activation of roomtemperature phosphorescence(RTP).The strategies and vital factors to activate RTP for CPD-based materials in both solid state and water were reviewed in detail to elaborate on the effect of the special structure on RTP generation.Furthermore,some perspectives on the current challenges were also provided to guide the further development of CPD-based room-temperature phosphorescent materials.

Dynamic Crosslinked Phosphorescent Poly(vinyl alcohol)-Terpyridine Films with Enhanced Mechanical Properties and Tunable Shape Memory

Achieving versatile room temperature phosphorescence(RTP)materials,especially with tunable mechanical properties and shape memory is attractive and essential but rarely reported.Here,a strategy was reported to realize multi-functional RTP films with multicolor fluorescence,ultralong afterglow,adjustable mechanical properties,and shape memory through the synergistic dynamic interaction of lanthanide(Ln~Ⅲ)-terpyridine coordination,borate ester bonds,and hydrogen bondings in a poly(vinyl alcohol)(PVA)matrix.By varying the amount of borax,the mechanical properties of the films could be finely controlled due to the change of crosslinking degree of dynamic borate ester bonds in PVA.The assembly and disassembly of borate ester bonds upon the trigger of borax and acid were applied as reversible linkage to achieve programmable shape memory behavior.In addition,the films displayed both fascinating multicolor fluorescence and ultralong afterglow characteristics due to the presence of Ln III doping and confinement of terpyridine in PVA.This study provides a new avenue to impart modulable mechanical strength and shape memory to RTP materials.

Switching on/off phosphorescent or non-radiative channels by aggregation-induced quantum interference

Pure organic materials with persistent and efficient room-temperature phosphorescence have recently aroused great research interest due to their vast potential in applications.One crucial design principle for such materials is to suppress as much as possible the non-radiative decay of the triplet exciton while maintaining a moderate phosphorescent radiative rate.However,molecular engineering often exhibits similar regulation trends for the two processes.Here,we propose that the quantum interference caused by aggregation can be utilized to control the phosphorescent and non-radiative decay channels.We systematically analyze various constructive and destructive transition pathways in aggregates with different molecular packing types and establish clear relationships between the luminescence characters and the signs of the singlet and triplet excitonic couplings.It is shown that the decay channels can be flexibly switched on or off by regulating the packing type and excitonic couplings.Most importantly,an enhanced phosphorescent decay and a completely suppressed non-radiative decay can be simultaneously realized in the aggregate packed with inversion symmetry.This work lays the theoretical foundation for future experimental realization of quantum interference effects in phosphorescence.

Highly efficient room temperature phosphorescent liquid crystalline polymer optical waveguides for advanced optoelectronics

Active organic optical waveguide materials(OOWMs)incorporating room temperature phosphorescence(RTP)hold significant promise for diverse applications in photonic and optoelectronic devices.Despite this potential,realizing active RTP optical waveguides with large-sized ordered structures and minimal light loss remains a formidable challenge.To address this issue,we present a groundbreaking thermoplastic active OOWM with low light loss,leveraging room temperature phosphorescent liquid crystalline polymer(LCP).This innovative material can be easily synthesized through the copolymerization of phosphorescent and liquid crystalline monomers.The resulting RTP copolymer exhibits a nematic liquid crystal phase with a phosphorescence lifetime of approximately 0.15 ms and an afterglow duration of around 1 second.Leveraging the excellent processability of LCP,we successfully produce meter-scale fibers via melt spinning.These RTP LCP fibers,characterized by a high orientation of mesogens along the fiber axis,demonstrate superior light confinement and efficient light conduction compared to unoriented samples,resulting in a low optical loss coefficient of 0.13 dB/mm.Furthermore,the thermal responsiveness of the RTP LCP optical waveguide enables its use as a photo switch.This pioneering work paves the way for the design of new OOWMs tailored for advanced photonics and optoelectronics devices.

A silane-based host material with improved electron transport properties for phosphorescent OLEDs with high efficiency and low efficiency roll-off

A dibenzosilole-based host material was designed and characterized.The host material,9,9'-(5,5-diphenyl-5H-dibenzo[b,d]silole-2,8-diyl)bis(9H-carbazole)(SSiCz),was designed to enhance the electron transport properties and rigidity by coupling two phenyl units of the tetraphenyl silane of a strong hole transport type bis(4-(9Hcarbazol-9-yl)phenyl)diphenylsilane host.The device efficiency roll-off was improved considerably by balancing the carriers in the phosphorescent organic light-emitting diodes(PhOLEDs),and the driving voltage at high luminance was reduced.The red and green PhOLEDs exhibited high external quantum efficiencies(EQEs)of 23.8%and 24.9%,respectively,and a relieved efficiency roll-off.In addition,S-SiCz was used as an electron transport type host with a hole transport type3,3'-di(9H-carbazol-9-yl)-1,1'-biphenyl host.The maximum EQEs of the red and green PhOLEDs using the mixed host were 26.0%and 25.5%,respectively,and EQE roll-off values were 18%and 6%,respectively.Therefore,the planarization design strategy of the host is effective for better device performance.

Recent advances in room-temperature phosphorescent materials by manipulating intermolecular interactions

Metal-free room-temperature phosphorescence(RTP)materials have the characteristics of large Stokes shift,long lifetime,and triplet state transition.They exhibit application potential in various fields,such as bioimaging,computer display,sensor,and anticounterfeiting and have drawn much research interest.Recent work showed that manipulating intermolecular interactions(e.g.,crystallization,polymerization,and rigid matrix)and host-guest assembly to restrain nonradiative transitions and isolate phosphor from oxygen as much as possible is a feasible way to obtain various types of efficient RTP materials.In some cases,intermolecular interactions also facilitated RTP emission by regulating the triplet state.On the other hand,heavy atoms(Br,I,etc.),heteroatoms(N,O,S,etc.),or carbonyls were introduced to the molecular skeleton through molecular engineering to enhance intersystem crossing,which is important for populating the triplet exciton.By comprehensively using the aforesaid strategies,great progress has been made for RTP materials.In this mini-review,we summarized recent advances in organic RTP materials based on manipulating intermolecular interactions.Typical host-guest assembly,hydrogen-bond assembly,energy transfer process,and exciplex emission system-based RTP materials were well illustrated.In summary,the current challenges and prospects for development in this field were presented.

An Ultralong Low-Temperature Phosphorescent Pentagonal-Prismatic Organometallic Cylinder Featuring Pentaphenylpyrrole-N-Heterocyclic Carbenes

A pentagonal-prismatic cylinder[Ag5(L)2](PF6)5 obtained from the pentaphenylpyrrole-bridged pentaimidazolium salt H5-L(PF6)5 and AgI ions was determined by X-ray diffraction analyses.The target organometallic cylinder not only exhibited enhanced fluorescence emission in dilute solution at room temperature but also showed an improved phosphorescence ratio compared with the free precursor and maintained a long lifetime(1.39 s)in the solid state at 77 K.Furthermore,the experimental results and DFT calculations confirmed that the formation of the organometallic cylinder promoted intersystem crossing.Meanwhile,the frontier orbitals of[Ag5(L)2](PF6)5 showed the main contribution of building block PPP as the luminescence source of[Ag5(L)2](PF6)5 by a modest heavy-atom effect.These results provide a strategy for constructing enhanced phosphorescent emission and long lifetime organometallic supramolecular phosphorescent materials.