High Phosphorescence Quantum Yield Research Articles

基于Re(Ⅰ)配合物有机电致发光器件的研究进展

The theoretical internal quantum efficiency of Re(Ⅰ) complexes is 100%,which is three times higher than that of fluorescence materials.The high quantum efficiency is attri-buted to the strong spin-orbit coupling of the heavy metal rhenium.Re(Ⅰ) complexes have the desirable properties including relatively short excited state lifetime,high phosphorescence quantum yield at room temperature,outstanding thermal stability and chemical stability.This review sketches the development of Re(Ⅰ) complexes in OLEDs which have been published.It also prospects the molecular designing and potential application future in OLEDs of Re(Ⅰ) complexes.

Phosphorescent self-assembled PtII tetranuclear metallocycles

A series of rigid Pt(II) diimine diacetylide complexes and their corresponding metallocyclic derivatives were synthesized through coordination-driven self-assembly. The photophysical properties of these complexes have been studied in detail, revealing exceptionally high RT phosphorescence quantum yields and lifetimes when the excited state becomes localized on the π-conjugated bridging-ligand following intramolecular charge-transfer sensitization.

Highly branched green phosphorescent tris-cyclometalated iridium(III) complexes for solution-processed organic light-emitting diodes

A series benzoimidazole-based dendritric complexes of iridium dendrimers containing Fréchet-type dendrons with peripheral fluorenyl surface groups have been synthesized. These iridium dendrimers are green-emitting with high phosphorescence quantum yield, and can be spin-coated as films of good quality. From cyclic voltammograms (CV), high onset potentials at 1.42–1.58 V due to the peripheral fluorene group were observed. Device from a second generation dendrimer 17 with structure of ITO/PEDOT:PSS/CBP: 20 wt% 17/TPBI/LiF/Al (PEDOT:PSS = poly(ethylene dioxythiophene): polystyrenesulfonate and CBP = bis( N-carbazolyl)biphenyl) has the best performance: maximum external quantum efficiency of 13.58% and maximum current efficiency of 45.7 cd/A. Space-charge-limited current (SCLC) flow technique was used to measure the mobility of charge carriers in the blend films of the compounds in CBP. Blend films of higher generation dendrimers have lower hole mobility, albeit with higher device efficiencies.

Specific Binding Effects for Cucurbit[8]uril in 2,4,6‐Triphenylpyrylium–Cucurbit[8]uril Host–Guest Complexes: Observation of Room‐Temperature Phosphorescence and their Application in Electroluminescence

2,4,6-Triphenylpyrylium (TP(+)) forms host-guest complexes with cucurbiturils (CBs) in acidic aqueous solutions. (1)H NMR spectroscopic data indicates that complexation takes place by encapsulation of the phenyl ring at the four position within CB. Formation of the complex with CB[6] and CB[7] leads to minor shifts in the fluorescence wavelength maximum (lambda(fl)) or quantum yield (Phi(fl)). In sharp contrast, for complexes with CB[8], the emission results in the simultaneous observation of fluorescence (lambda(fl)=480 nm, Phi(fl)=0.05) and room-temperature phosphorescence (lambda(ph)=590 nm, Phi(ph)=0.15). The occurrence of room-temperature phosphorescence can be used to detect the presence of CB[8] visually in solution. Molecular modeling and MM2 molecular mechanics calculations suggest that this effect arises from locking the conformational mobility of the 2- and 6-phenyl rings as a result of CB[8] encapsulation. The remarkably high room-temperature phosphorescence quantum yield of the TP(+)@CB[8] complex has been advantageously applied to develop an electroluminescent cell that contains this host-guest complex. In contrast, analogous cells prepared with TP(+) or TP(+)@CB[7] fail to exhibit electroluminescence.

Synthesis, Characterization, and DFT/TD-DFT Calculations of Highly Phosphorescent Blue Light-Emitting Anionic Iridium Complexes

Highly phosphorescent blue-light-emitting anionic iridium complexes (C4H9)4N[Ir(2-phenylpyridine)2(CN)2] (1), (C4H9)4N[Ir(2-phenyl-4-dimethylaminopyridine)2(CN)2] (2), (C4H9)4N[Ir(2-(2,4-difluorophenyl)-pyridine)2(CN)2] (3), (C4H9)4N[Ir(2-(2,4-difluorophenyl)-4-dimethylaminopyridine)2(CN)2] (4), and (C4H9)4N[Ir(2-(3,5-difluorophenyl)-4-dimethylaminopyridine)2(CN)2] (5) were synthesized and characterized using NMR, UV-vis absorption, and emission spectroscopy and electrochemical methods. In these complexes color and quantum yield tuning aspects are demonstrated by modulating the ligands with substituting donor and acceptor groups on both the pyridine and phenyl moieties of 2-phenylpyridine. Complexes 1-5 display intense photoluminescence maxima in the blue region of the visible spectrum and exhibit very high phosphorescence quantum yields, in the range of 50-80%, with excited-state lifetimes of 1-4 micros in acetonitrile solution at 298 K. DFT and time dependent-DFT calculations were performed on the ground and excited states of the investigated complexes to provide insight into the structural, electronic, and optical properties of these systems.

N∧C∧N‐Coordinated Platinum(II) Complexes as Phosphorescent Emitters in High‐Performance Organic Light‐Emitting Devices

Abstract A series of terdentate cyclometallated PtII complexes with remarkable luminescence properties are used as new phosphorescence‐emitting dopants in a blended host matrix as the emitting layer, resulting in very high electroluminescence efficiencies. Because of the high phosphorescence quantum yields of these Pt complexes and the efficient energy transfer from both singlet and triplet excited states of the host to the emitting guest, external electroluminescence quantum efficiencies as high as 4–16 % photons per carrier and luminous efficiencies of 15–40 cd A–1 are achieved. Moreover, these high efficiency values were maintained over a four‐decade current intensity span with no significant roll‐off. Tuning of the electroluminescence spectra from the yellow to the green‐bluish region of the chromaticity diagram is obtained simply by changing the substituents at the central 5‐position of the cyclometallating ligand.

Absorption and emission spectroscopic characterization of platinum-octaethyl-porphyrin (PtOEP)

The absorption and emission spectroscopic behaviour of the platinum complexed porphyrin PtOEP (platinum-octaethyl-porphyrin) is studied at room temperature. Liquid solutions, doped films, and a neat film are investigated. The absorption cross-section spectra including singlet–triplet absorption, the triplet–singlet stimulated emission cross-section spectra, the phosphorescence quantum distributions, the phosphorescence quantum yields, and the phosphorescence signal decays are determined. In the neat film a red-shifted phosphorescent excimer emission is observed. In diluted solid solution (polystyrene and dicarbazole-biphenyl films) as well as in de-aerated liquid solutions (tetrahydrofuran, toluene, chloroform) high phosphorescence quantum yields are obtained. In air-saturated liquid solutions, the phosphorescence efficiency is reduced by oxygen quenching. At intense short-pulse laser excitation the phosphorescence lifetime is shortened by triplet–triplet annihilation. No amplification of spontaneous emission was observed.

Absorption and emission spectroscopic characterization of Ir(ppy)3

Abstract The absorption and emission spectroscopic behaviour of cyclometalated fac -tris(2-phenylpyridine) iridium(III) [Ir(ppy) 3 ] is studied at room temperature. Liquid solutions, doped films, and neat films are investigated. The absorption cross-section spectra including singlet–triplet absorption, the triplet–singlet stimulated emission cross-section spectra, the phosphorescence quantum distributions, the phosphorescence quantum yields and the phosphorescence signal decays are determined. In neat films fluorescence self-quenching occurs, in diluted solid solution (polystyrene and dicarbazole-biphenyl films) as well as deaerated liquid solution (toluene) high phosphorescence quantum yields are obtained, and in air-saturated liquid solutions (chloroform, toluene, tetrahydrofuran) the phosphorescence efficiency is reduced by triplet oxygen quenching. At intense short-pulse laser excitation the phosphorescence lifetime is shortened by triplet–triplet annihilation. No amplification of spontaneous emission in the phosphorescence spectral region was observed indicating higher excited-state absorption than stimulated emission.

Photochemistry and photopolymerization activities of novel phenylthiobenzophenone and diphenylthiophene photoinitiators

The photoinduced polymerization activities of seven novel phenylthio substituted benzophenones have been determined and compared to that of benzophenone itself in different monomers and prepolymers using real time infra-red (RTi.r.) and pencil hardness methods. Four novel dibenzopthiophene compounds have also been include in the investigation to examine the influence of bridging the sulfur atom between the benzophenone chromophore and phenyl groups via an alicyclic bridge. Absorption, fluorescence and phosphorescence analysis, as well as photoreduction/photolysis studies have been undertaken on the compounds and the data is inter-related to their photopolymerization activities. Fluorescence and phosphorescence analysis indicates a high rate of intersystem crossing to the triplet state. The latter is essentially a mixed excited nπ/ππ∗ state in nature for the phenylthio derivatives as indicated by the phosphorescence lifetime data and quantum yields of emission. In comparison the dibenzopthiophenes retained much of their nπ∗ character coupled with a rigid molecular structure giving rise to very high phosphorescence quantum yields. Compared with benzophenone all the phenylthio derivatives exhibit higher activity using commercial pencil hardness curing. Strong synergism is also observed with a tertiary amine compared to the activities of the dibenzothiophenes. This is also generally reflected in the RTi.r. data. The dibenzothiophenes exhibit lower activities than the phenylthio derivatives, but remained somewhat greater than that of benzophenone. The enhanced photoactivities of the phenylthio derivatives are associated with their higher extinction coefficients and longer wavelength absorptions in the near ultra-violet region above 300 nm. Steric effects in the case of the dibenzopthiophenes are responsible for their poor synergism with tertiary amines. Their photoreduction quantum yields in the presence of an amine match exactly their photopolymerization effects determined by RTi.r. Microsecond flash photolysis showed weak ketyl radical formation in the region 500–600 nm due to hydrogen atom abstraction by the excited triplet state of the benzophenone chromophore in both structures. Significant transient absorption in region 300–400 nm is suggestive of side chain scission giving rise to additional aryl radical species.

Photochemistry and photocuring activities of novel substituted 4′-(4-methylphenylthio) benzophenones as photoinitiators

The photoinduced polymerization activities of 19 novel substituted 4′-(4-methylphenylthio)benzophenones (or 4′-(4-tolylthio)-benzophenones) were determined and compared with that of the unsubstituted derivative itself in different monomers and prepolymers using real-time infrared (RTFTIR) and pencil hardness methods. Absorption, fluorescence and phosphorescence analyses, as well as photoreduction/photolysis studies, were undertaken on the compounds, and the data were related to the photopolymerization activities. Solvent shift studies on the absorption maxima of all the compounds indicate the presence of a long-wavelength single ππ ∗ state with some nπ ∗ character. The absorption maxima of the bistolythio, amino, chloro and nitro derivatives are more red shifted than those of the simpler alkyl, alkoxy, phenyl and phenoxy derivatives. Fluorescence and phosphorescence analyses indicate a high rate of intersystem crossing to the triplet state. The fluorescence emission maxima are markedly red shifted with increasing solvent polarity, indicating that the lowest excited singlet state exhibits a high degree of charge transfer character. The lowest excited triplet state of all the 4-substituted 4-tolythiobenzophenones is essentially a ππ ∗ configuration, with some nπ ∗ character, as indicated by the phosphorescence lifetime data. The lowest excited triplet state of the unsubstituted derivative, on the other hand, is essentially ππ ∗ in character with a longer emission lifetime and a lower quantum yield. The emission maxima are independent of the nature of the substitution, indicating the presence of a rigid molecular structure. The latter is confirmed by the observation of very high phosphorescence quantum yields. The bistolythio derivatives exhibit shorter phosphorescence emission lifetimes, indicating that their lowest excited triplet state is nπ ∗ in nature. The triplet ππ ∗ character of the amino derivatives is indicated by their increased emission lifetimes. The electron-withdrawing effect of the chloro and nitro groups markedly reduces the phosphorescence quantum yield. These effects are accounted for by the relative spacings of close-lying lowest excited singlet ππ ∗ and second excited triplet nπ ∗ states controlling the competitive processes of internal conversion and intersystem crossing. Compared with the unsubstituted 4-tolylthio derivative, all the alkyl-, alkoxy-, phenyl- and phenoxy-substituted derivatives exhibit higher activities as photoinitiators in the absence of an amine cosynergist. Lengthening or broadening of the alkoxy substituent also gives rise to an increased photoinitiation activity, whereas alkyl groups are less effective. The presence of an amine cosynergist enhances photocuring, giving rise to variable effects depending on the nature of the triplet exciplex interaction. The bistolythio derivatives exhibit the highest photoinitiation activity, whereas the 4-nitro group has a marked deactivating effect. The presence of the 4-amino group also enhances the photoinitiation activity, but only by RTFTIR measurements. The photoreduction/photolysis rates of all the 4-substituted derivatives are greater than that of the unsubstituted derivative and show some relation to the nature of the lowest excited triplet state. The photophysical and photochemical data are discussed in relation to the relative, photoactivities of the compounds as photoinitiators for curing acrylated multifunctional monomers.

Evaluation of a time-resolved fluorescence microscope using a phosphorescent Pt-porphine model system.

A time-resolved fluorescence microscope is presented that allows the sensitive detection of delayed luminescent labels with decay times from one microsecond to several milliseconds. The microscope utilizes an argon ion laser chopped with an acoustooptical modulator as excitation light source in combination with a gated multichannel plate image intensifier in the image plane. A theoretical model for the detection efficiency of practically any time-resolved fluorescence microscope is verified using phosphorescent Pt-porphine-stained Sephadex beads. The detection efficiency of the presented setup was shown to be 42%, which is near the theoretical limit of 50% for non-saturated luminescent dyes. The suppression of prompt fluorescence signals was found to be 1:5,500. The Pt-porphine beads proved to be an excellent model system for time-resolved fluorescence microscopy, showing a high extinction coefficient and high phosphorescence quantum yield in aqueous environment under room temperature conditions. Furthermore, for the microscope described the decay time of the Pt-porphine beads of 47 microseconds is long enough to enable efficient suppression of the prompt fluorescence while maintaining a high excitation and emission duty cycle. This is considered to be of vital importance in order not to saturate the luminescence with the excitation intensities commonly used in fluorescence microscopy.

Physicochemical Interactions of the Isomers of Aminobenzoic Acid with Sodium Acetate in Solid-Matrix Room-Temperature Luminescence Spectroscopy

The room-temperature fluorescence and room-temperature phosphorescence quantum yields of the isomers of aminobenzoic acid adsorbed on sodium acetate were obtained. These data were correlated with solution fluorescence data and diffuse reflectance infrared spectral data from the three isomers. The results yielded insights into the bonding interactions of the aminobenzoic acid isomers with sodium acetate. In particular, the specific structural and bonding characteristics of the isomers with sodium acetate were very important in determining whether a high room-temperature phosphorescence quantum yield would be obtained from a given isomer.

Quantum-chemical investigation of Franck-Condon and Jahn-Teller activity in the electronic spectra of Buckminsterfullerene

Quantum-chemical results are reported which indicate that the absorption, fluorescence and phosphorescence spectra of Buckminsterfullerene are governed by a 1T1u ← 1Ag, 1T2g → 1Ag and 3T2g → 1Ag transition, respectively. Normal modes are calculated and their Franck-Condon and Jahn-Teller activity in these spectra are evaluated, along with the Jahn-Teller distortion of the radical anion. Vibrational progressions are expected to be short. A high phosphorescence quantum yield is predicted.