Performance Improvement of Organic Light Emitting Diodes Using Poly(N-vinylcarbazole) (PVK) as a Blocking Layer

High efficiency organic light‐emitting‐devices (OLED) have been fabricated by incorporation of a polymeric layer as a controller of the unbalanced charge. In device configuration of ITO/PEDOT:PSS/PVK/Alq₃/LiF:Al, poly(N‐vinylcarbazole) (PVK) was selected as a block‐ing layer (BL) because it has a hole transporting property and a higher band gap, especially a lower LUMO level than the emitting layer (Alq₃) and a higher HOMO level than the hole injection layer (PEDOT: PSS). As a result, the optimal structure with this bl layer showed a peak efficiency of 6.89 cd/A and 2.30 lm/W compared to the device without the PVK layer of 1.08 cd/A, 0.27 lm/W. This result shows that the PVK layer could effec‐tively block the electrons from metal cathode and confine them in the emitting layer and accomplish the charge balance, which leads to enhanced hole‐electron balance for achieving high recombination efficiency.     

Precise Control of Intramolecular Charge‐Transport: The Interplay of Distance and Conformational Effects

A new series of donor–bridge–acceptor (D–B–A) compounds consisting of π‐conjugated oligofluorene (oFL) bridges between a ferrocene (Fc) electron‐donor and a fullerene (C₆₀) electron‐acceptor have been synthesized. In addition to varying the length of the bridge (i.e., mono‐ and bi‐fluorene derivatives), four different ways of linking ferrocene to the bridge have been examined. The Fc moiety is linked to oFL: 1) directly without any spacer, 2) by an ethynyl linkage, 3) by a vinylene linkage, and 4) by a p‐phenylene unit. The electronic interactions between the electroactive species have been characterized by cyclic voltammetry, absorption, fluorescence, and transient absorption spectroscopy in combination with quantum chemical calculations. The calculations reveal exceptionally close energy‐matching between the Fc and the oFL units, which results in strong electronic‐coupling. Hence, intramolecular charge‐transfer may easily occur upon exciting either the oFLs or Fcs. Photoexcitation of Fc–oFL–C₆₀ conjugates results in transient radical‐ion‐pair states. The mode of linkage of the Fc and FL bridge has a profound effect on the photophysical properties. Whereas intramolecular charge‐separation is found to occur rather independently of the distance, the linker between Fc and oFL acts (at least in oFL) as a bottleneck and significantly impacts the intramolecular charge‐separation rates, resulting in beta values between β_CS 0.08 and 0.19 Å^?1. In contrast, charge recombination depends strongly on the electron‐donor–acceptor distance, but not at all on the linker. A value of β_CR (0.35±0.01 Å^?1) was found for all the systems studied. Oligofluorenes prove, therefore, to be excellent bridges for probing how small structural variations affect charge transport in D–B–A systems.     

Light‐emitting diodes and lasers based on polymer films doped with small organic molecules and rare‐earth complexes

We investigated the lasing properties of optically pumped polymer films. Amplified spontaneous emission (ASE) around 400 nm was observed in polymer films of polystyrene (PS) and poly(N‐vinylcarbazole) (PVK) doped up to 20% with the hole‐transporting organic molecule N,N′‐bis(3‐methylphenyl)‐N,N′‐diphenylbenzidine (TPD). Thus, TPD‐based films are candidates for blue‐emitting organic diode lasers. Films containing several semiconducting organic molecules and polymers and rare‐earth complexes were also investigated. Energy transfer was observed in PVK films doped with various europium and samarium complexes. PS films containing the electron‐transporting organic molecule 2‐(4‐biphenylyl)‐5‐(4‐tert‐butylphenyl)‐1,3,4‐oxadiazole and small amounts of TPD also showed energy transfer to the europium complexes, but not to the samarium ones. None of these films demonstrated ASE; therefore, they are not appropriate for lasing purposes. However, because rare‐earth ions have very sharp emission spectra, these materials are candidates for very monochromatic light‐emitting diodes. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2706–2714, 2003     

Combining Charge‐Transfer Pathways to Achieve Unique Thermally Activated Delayed Fluorescence Emitters for High‐Performance Solution‐Processed,Non‐doped Blue OLEDs

Two efficient blue thermally activated delayed fluorescence compounds, B‐oCz and B‐oTC , composed of ortho‐donor (D)–acceptor (A) arrangement were designed and synthesized. The significant intramolecular D–A interactions induce a combined charge transfer pathway and thus achieve small ΔE _ST and high efficiencies. The concentration quenching can be effectively inhibited in films of these compounds. The blue non‐doped organic light emitting diodes (OLEDs) based on B‐oTC prepared from solution processes shows record‐high external quantum efficiency (EQE) of 19.1 %.     

Combining Charge‐Transfer Pathways to Achieve Unique Thermally Activated Delayed Fluorescence Emitters for High‐Performance Solution‐Processed,Non‐doped Blue OLEDs

Two efficient blue thermally activated delayed fluorescence compounds, B‐oCz and B‐oTC , composed of ortho‐donor (D)–acceptor (A) arrangement were designed and synthesized. The significant intramolecular D–A interactions induce a combined charge transfer pathway and thus achieve small ΔE _ST and high efficiencies. The concentration quenching can be effectively inhibited in films of these compounds. The blue non‐doped organic light emitting diodes (OLEDs) based on B‐oTC prepared from solution processes shows record‐high external quantum efficiency (EQE) of 19.1 %.     

A novel planar D‐A alternating copolymer with D‐A integrated structures exhibiting H‐aggregate behaviors for polymer solar cells

With the D‐A integrated structure concept, a new donor–acceptor (D‐A) copolymer poly{(N‐dodecyl‐carbazole[3,4‐c:5,6‐c]bis[1,2,5]thiadiazole‐alt‐4,8‐di(2‐ethylhexy‐loxyl)benzo[1,2‐b:4,5‐b′]dithiophene)} has been designed and synthesized using a novel architecture N‐dodecyl‐carbazole[3,4‐c:5,6‐c]bis[1,2,5]thiadiazole, and di(2‐ethylhexy‐loxyl)benzo[1,2‐b:4,5‐b′]dithiophene) as the basic building blocks. The copolymer has a low‐lying highest occupied molecular orbital energy level of ?5.41 eV and a broaden absorption matching well with the main solar photon flux. Note that an H‐aggregation beneficial for charge transportation and collection is formed in the macromolecules film, which implies that the planar D‐A integrated structure favors the strong intermolecular interaction to render molecules aggregated via face‐to‐face self‐assembly. The aggregation becomes larger scale after thermal annealing. Additionally, obvious intramolecular charge transfer and energy transfer have occurred in created D‐A integration. Without any treatment, the resulting polymer achieved a efficiency of 2.0% and relatively high open‐circuit voltage (V_oc) value of 0.77 V when blended with [6,6]‐phenyl‐C61‐butyric acid methyl ester in a typical bulk heterojunction. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

The Origin of the Improved Efficiency and Stability of Triphenylamine‐Substituted Anthracene Derivatives for OLEDs: A Theoretical Investigation

Herein, we describe the molecular electronic structure, optical, and charge‐transport properties of anthracene derivatives computationally using density functional theory to understand the factors responsible for the improved efficiency and stability of organic light‐emitting diodes (OLEDs) with triphenylamine (TPA)‐substituted anthracene derivatives. The high performance of OLEDs with TPA‐substituted anthracene is revealed to derive from three original features in comparison with aryl‐substituted anthracene derivatives: 1) the HOMO and LUMO are localized separately on TPA and anthracene moieties, respectively, which leads to better stability of the OLEDs due to the more stable cation of TPA under a hole majority‐carrier environment; 2) the more balanceable hole and electron transport together with the easier hole injection leads to a larger rate of hole–electron recombination, which corresponds to the higher electroluminescence efficiency; and 3) the increasing reorganization energy for both hole and electron transport and the higher HOMO energy level provide a stable potential well for hole trapping, and then trapped holes induce a built‐in electric field to prompt the balance of charge‐carrier injection.     

Engineering the Interconnecting Position of Star‐Shaped Donor–π–Acceptor Molecules Based on Triazine,Spirofluorene, and Triphenylamine Moieties for Color Tuning from Deep Blue to Green

Pi‐conjugated organic molecules featuring the donor–bridge–acceptor (D–π–A) structure have been widely used in semiconducting materials owing to their rigid structure, good thermal stability, excellent charge transfer, and high emission efficiency. To investigate the effect of the D–π–A molecular structure on the photophysical properties, in this contribution, three star‐shaped D–π–A isomers based on the 2,4,6‐triphenyl‐1,3,5‐triazine, spirofluorene, and triphenylamine moieties, that is, p‐TFTPA, mp‐TFTPA, and m‐TFTPA, were synthesized by elaborately engineering the interconnecting position in the building‐block units. The optophysical properties of these compounds were systematically explored by experiments and theory calculations. Definitively, changing the interconnecting position in these molecules played a significant role in the degree of π conjugation, which resulted in tunable emission colors from deep blue to green. Moreover, these isomers were employed as emissive dopants in organic light‐emitting diodes. The highest external quantum efficiency of 2.3 % and current efficiency of 6.2 cd A^?1 were achieved by using the p‐TFTPA based device. This research demonstrates a feasible way to realize blue emitters by engineering D–π–A conjugation.     

Donor/Acceptor Effects on the Linear and Nonlinear Optical Properties of Geminal Diethynylethenes (g‐DEEs)

A series of geminal diethynylethenes (g‐DEEs) with electron‐donating and/or electron‐accepting (D/A) groups were synthesized via a Pd‐catalyzed cross‐coupling sequence. The UV/VIS spectra for donor–acceptor (D–A) functionalized g‐DEEs 5, 8 , and 11 show distinctive absorption trends attributable to intramolecular charge‐transfer (ICT). The bond‐length‐alternation (BLA) index for the cross‐conjugated enediyne framework varies slightly with different terminal substituents as determined by density‐functional theory (DFT) calculations and single‐crystal X‐ray analysis. Ultrafast third‐order optical nonlinearities for the g‐DEEs were measured by the differential optical Kerr effect (DOKE) technique and show that terminal donor–acceptor substitution of g‐DEEs enhances molecular second hyperpolarizabilities (γ) in comparison to donor or acceptor g‐DEEs. A small increase in the two‐photon‐absorption cross‐section (σ⁽²⁾) is observed in the series 9 – 11 as a result of increased functionalization. The effects of donor/acceptor substitution on electron delocalization along the cross‐conjugated enediyne structure are evaluated on the basis of natural‐bond‐orbital (NBO) analysis. Solid‐state structures of the four derivatives 3b, 4b, 7 and 8 were characterized by single‐crystal X‐ray structural analysis and show an asymmetric unit cell for one derivative, D–A g‐DEE 8 .     

Efficient Deep‐Blue Electroluminescence Based on Phenanthroimidazole‐Dibenzothiophene Derivatives with Different Oxidation States of the Sulfur Atom

Developing efficient deep‐blue materials is a long‐term research focus in the field of organic light‐emitting diodes (OLEDs). In this paper, we report two deep‐blue molecules, PITO and PISF, which share similar chemical structures but exhibit different photophysical and device properties. These two molecules consist of phenanthroimidazole and dibenzothiophene analogs. The distinction of their chemical structures lies in the different oxidation states of the S atom. For PITO, the S atom is oxidized and the resulting structure dibenzothiophene S,S‐dioxide becomes electron deficient. Therefore, PITO displays remarkable solvatochromism, implying a charge‐transfer (CT) excited state formed between the donor (D) phenanthroimidazole and acceptor (A) dibenzothiophene S,S‐dioxide. For PISF, it is constituted of phenanthroimidazole and dibenzothiophene in which the S atom is not oxidized. PISF displays locally excited (LE) emission with little solvatochromism. Compared with PISF, the D–A molecule PITO with an electron‐deficient group shows a much lower LUMO energy level, which is in favor of electron injection in device. In addition, PITO exhibits more balanced carrier transport. However, PISF is capable of emitting in the shorter wavelength region, which is beneficial to obtain better color purity. The doped electroluminescence (EL) device of the D–A molecule PITO manifests deep‐blue emission with CIE coordinates of (0.15, 0.08) and maximum external quantum efficiency (EQE) of 4.67 %. The doped EL device of the LE molecule PISF, however, reveals an even bluer emission with CIE coordinates of (0.15, 0.06) and a maximum EQE of 4.08 %.     

Acid–Base‐Responsive Intense Charge‐Transfer Emission in Donor–Acceptor‐Conjugated Fluorophores

Herein we report on the synthesis and acid‐responsive emission properties of donor–acceptor (D–A) molecules that contain a thienothiophene unit. 2‐Arylthieno[3,2‐b]thiophenes were conjugated with an N‐methylbenzimidazole unit to form acid‐responsive D–A‐type fluorophores. The D–A‐conjugated fluorophores showed intense intramolecular charge‐transfer (ICT) emission in response to acid. The effect of the substitution on their photophysical properties as well as their solvent‐dependence indicated non‐twisting ICT emission in protonated D–A molecules. The quinoidal character of 2‐arylthienothiophene as a donor part is discussed, as it is assumed that it contributes to suppression of the molecular twisting in the excited state, therefore decreasing the nonradiative rate constant, thereby resulting in the intense ICT emission. Acid–base‐sensitive triple‐color emission was also achieved by the introduction of a base‐responsive phenol group in the donor part.     

Synthesis,characterization, and electroluminescence of PPV copolymers containing electron and hole‐transporting units

Three series of poly(phenylene vinylene) (PPV) derivatives containing hole‐transporting triphenylamine derivatives [N‐(4‐octoxylphenyl)diphenylamine, N,N′‐di(4‐octyloxylphenyl)‐N,N′‐diphenyl‐1,4‐phenylenediamine, and N,N′‐di(4‐octoxylphenyl)‐N,N′‐diphenylbenzidine] (donor) and electron‐transporting oxadiazole unit (2,5‐diphenyl‐1,3,4‐oxadiazole) (acceptor) in the main chain were synthesized by improved Wittig copolymerization. The resulting donor–acceptor (D‐A) polymers are readily soluble in common organic solvents, such as chloroform, dichloroethane, THF, and toluene. The polymers containing oxadiazole group exhibit good thermal stability with 5% weight loss above 400 °C. The intramolecular charge‐transfer was observed in these D‐A polymers. In comparison with corresponding polymers without oxadiazole unit, the single‐layer devices based on the D‐A polymers showed much improved electroluminescent properties, because of the balanced charge injection and transport. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1566–1576, 2008     

吩噻嗪给体受体衍生物激发态的电荷转移

A series of N-bonded donor-acceptor derivatives of phenothiazine containing phenyl （PHPZ）, anisyl （ANPZ）, pyridyl （PYPZ）, naphthyl （NAPZ）, acetylphenyl （APPZ）, and cyanophenyl （CPPZ） as an electron acceptor have been synthesized. Their photophysical properties were investigated in solvents of different polarities by absorption and emission techniques. These studies clearly revealed the existence of an intramolecular charge transfer （ICT） excited state in the latter four compounds. The solvent dependent Stokes shift values were analyzed by the modified Lippert-Mataga equation to obtain the excited state dipole moment values. The large excited state dipole moment suggests that the full （or nearly full） electron transfer take place in the A-D systems. In the system of A-D phenothiazine derivatives, the transition dipole moments Mflu were determined mainly by direct interactions between the solvent-equilibrated fluorescence ^1CT state and ground state because of their lack of significant change with increase of the solvent polarity. The electron structure and molecular conformation of phenothiazine derivatives will be significantly changed with the increase of the electron affinity of the N-10 substituent.     

Self‐Assembled Architectures with Segregated Donor and Acceptor Units of a Dyad Based on a Monopyrrolo‐Annulated TTF–PTM Radical

An electron donor–acceptor dyad based on a polychlorotriphenylmethyl (PTM) radical subunit linked to a tetrathiafulvalene (TTF) unit through a π‐conjugated N‐phenyl–pyrrole–vinylene bridge has been synthesized and characterized. The intramolecular electron transfer process and magnetic properties of the radical dyad have been evaluated by cyclic voltammetry, UV/Vis spectroscopy, vibrational spectroscopy, and ESR spectroscopy in solution and in the solid state. The self‐assembling abilities of the radical dyad and of its protonated non‐radical analogue have been investigated by X‐ray crystallographic analysis, which revealed that the radical dyad produced a supramolecular architecture with segregated donor and acceptor units in which the TTF subunits were arranged in 1D herringbone‐type stacks. Analysis of the X‐ray data at different temperatures suggests that the two inequivalent molecules that form the asymmetric unit of the crystal of the radical dyad evolve into an opposite degree of electronic delocalization as the temperature decreases.     

Unambiguous Diagnosis of Photoinduced Charge Carrier Signatures in a Stoichiometrically Controlled Semiconducting Polymer‐Wrapped Carbon Nanotube Assembly

Single‐walled carbon nanotube (SWNT)‐based nanohybrid compositions based on (6,5) chirality‐enriched SWNTs ([(6,5) SWNTs]) and a chiral n‐type polymer (S‐PBN(b)‐Ph₄PDI) that exploits a perylenediimide (PDI)‐containing repeat unit are reported; S‐PBN(b)‐Ph₄PDI‐[(6,5) SWNT] superstructures feature a PDI electron acceptor unit positioned at 3 nm intervals along the nanotube surface, thus controlling rigorously SWNT–electron acceptor stoichiometry and organization. Potentiometric studies and redox‐titration experiments determine driving forces for photoinduced charge separation (CS) and thermal charge recombination (CR) reactions, as well as spectroscopic signatures of SWNT hole polaron and PDI radical anion (PDI^?.) states. Time‐resolved pump–probe spectroscopic studies demonstrate that S‐PBN(b)‐Ph₄PDI‐[(6,5) SWNT] electronic excitation generates PDI^?. via a photoinduced CS reaction (τ_CS≈0.4 ps, Φ_CS≈0.97). These experiments highlight the concomitant rise and decay of transient absorption spectroscopic signatures characteristic of the SWNT hole polaron and PDI^?. states. Multiwavelength global analysis of these data provide two charge‐recombination time constants (τ_CR≈31.8 and 250 ps) that likely reflect CR dynamics involving both an intimately associated SWNT hole polaron and PDI^?. charge‐separated state, and a related charge‐separated state involving PDI^?. and a hole polaron site produced via hole migration along the SWNT backbone that occurs over this timescale.     

Triarylboranes with a 2‐Dimesitylboryl‐2’‐(N,N‐dimethylamino)biphenyl Core Unit: Structure–Property Correlations and Sensing Abilities to Discriminate Between F− and CN− Ions

A series of triarylboranes, in which different substituents are introduced at the para position of the dimethylamino group of a 2‐dimesitylboryl‐2’‐(N,N‐dimethylamino)biphenyl core unit, have been comprehensively investigated to explore the effect of structural modification on photophysical properties. The introduction of electron‐accepting substituents would facilitate the HOMO→LUMO charge transfer (CT) transition. In contrast, the intramolecular CT transition is significantly prohibited when electron‐donating substituents are incorporated. Notably, the HOMO→LUMO CT transition mainly consists of the transition from the electron‐donating amino group to an electron acceptor other than boryl when a strong electron acceptor such as the dicyanovinyl group is present. This dicyanovinyl‐substituted compound displays sensing abilities to discriminate fluoride and cyanide ions. In solution in THF, the fluoride ions first bind to the boron center, then attack the α‐carbon atom of the dicyanovinyl group, whereas the cyanide anion acts on the electron‐accepting centers in the reverse sequence. As a result, the absorption and emission change in different manners upon addition of fluoride and cyanide ions.     

Integration of the 1,2,3‐Triazole “Click” Motif as a Potent Signalling Element in Metal Ion Responsive Fluorescent Probes

In a systematic approach we synthesized a new series of fluorescent probes incorporating donor–acceptor (D‐A) substituted 1,2,3‐triazoles as conjugative π‐linkers between the alkali metal ion receptor N‐phenylaza‐[18]crown‐6 and different fluorophoric groups with different electron‐acceptor properties (4‐naphthalimide, meso‐phenyl‐BODIPY and 9‐anthracene) and investigated their performance in organic and aqueous environments (physiological conditions). In the charge‐transfer (CT) type probes 1 , 2 and 7 , the fluorescence is almost completely quenched by intramolecular CT (ICT) processes involving charge‐separated states. In the presence of Na⁺ and K⁺ ICT is interrupted, which resulted in a lighting‐up of the fluorescence in acetonitrile. Among the investigated fluoroionophores, compound 7 , which contains a 9‐anthracenyl moiety as the electron‐accepting fluorophore, is the only probe which retains light‐up features in water and works as a highly K⁺/Na⁺‐selective probe under simulated physiological conditions. Virtually decoupled BODIPY‐based 6 and photoinduced electron transfer (PET) type probes 3 – 5 , where the 10‐substituted anthracen‐9‐yl fluorophores are connected to the 1,2,3‐triazole through a methylene spacer, show strong ion‐induced fluorescence enhancement in acetonitrile, but not under physiological conditions. Electrochemical studies and theoretical calculations were used to assess and support the underlying mechanisms for the new ICT and PET 1,2,3‐triazole fluoroionophores.     

Intermolecular Charge‐Transfer Transition Emitter Showing Thermally Activated Delayed Fluorescence for Efficient Non‐Doped OLEDs

A novel molecular model of connecting electron‐donating (D) and electron‐withdrawing (A) moieties via a space‐enough and conjugation‐forbidden linkage (D‐Spacer‐A) is proposed to develop efficient non‐doped thermally activated delayed fluorescence (TADF) emitters. 10‐(4‐(4‐(4,6‐diphenyl‐1,3,5‐triazin‐2‐yl) phenoxy) phenyl)‐9,9‐dimethyl‐9,10‐dihydroacridine (DMAC‐o‐TRZ) was designed and synthesized accordingly. As expected, it exhibits local excited properties in single‐molecule state as D‐Spacer‐A molecular backbone strongly suppress the intramolecular charge‐transfer (CT) transition. And intermolecular CT transition acted as the vital radiation channel for neat DMAC‐o‐TRZ film. As in return, the non‐doped device exhibits a remarkable maximum external quantum efficiency (EQE) of 14.7 %. These results prove the feasibility of D‐Spacer‐A molecules to develop intermolecular CT transition TADF emitters for efficient non‐doped OLEDs.     

Oligo(p‐phenyleneethynylene) (OPE) Molecular Wires: Synthesis and Length Dependence of Photoinduced Charge Transfer in OPEs with Triarylamine and Diaryloxadiazole End Groups

The systematic synthesis and photophysical, electrochemical and computational studies on an extended series of triphenylamine‐[C?C‐1,4‐C₆H₂(OR)₂]_n‐C?C‐diphenyl‐1,3,4‐oxadiazole dyad molecules (the OR groups are at 2,5‐positions of the para‐phenylene ring and R=C₆H₁₃; n=0–5, compounds 1 , 2 , 3 , 4 and 5 , respectively) are reported. Related molecules with identical end groups, triphenylamine‐C?C‐1,4‐C₆H₂(OR)₂‐C?C‐triphenylamine (R=C₆H₁₃; 6 ) and diphenyl‐1,3,4‐oxadiazole‐[C?C‐C₆H₂(OR)₂]₂‐C?C‐diphenyl‐1,3,4‐oxadiazole (R=C₆H₁₃; 7 ) were also studied. These D–B–A 1 – 5 , D–B–D 6 and A–B–A 7 (D=electron donor, B=bridge, A=electron acceptor) systems were synthesized using palladium‐catalysed cross‐coupling reactions of new p‐phenyleneethynylene building blocks. Steady‐state emission studies on the dyads 1 – 5 reveal a complicated behavior of the emission that is strongly medium dependent. In low polarity solvents the emission is characterized by a sharp high‐energy peak attributed to fluorescence from a locally excited (LE) state. In more polar environments the LE state is effectively quenched by transfer into an intramolecular charge‐transfer (ICT) state. The medium dependence is also observed in the quantum yields (QYs) which are high in cyclohexane and low in acetonitrile, thus also indicating charge‐transfer character. Low‐temperature emission spectra for 2 – 5 in dichloromethane and diethyl ether also reveal two distinct excited states, namely the LE state and the conventional ICT state, depending on solvent and temperature. Hybrid DFT calculations for 1 – 7 establish that the OPE bridge is involved in both frontier orbitals where the bridge character increases as the bridge length increases. Computed TD‐DFT data on 1 – 5 assign the emission maxima in cyclohexane as LE transitions. Each time‐resolved emission measurement on 2 – 7 in cyclohexane and diethyl ether reveals a wavelength dependent bi‐exponential decay of the emission with a fast component in the 5–61 ps range on blue detection and a slower approximately 1 ns phase, independent of detection wavelength. The fast component is attributed to LE fluorescence and this emission component is rate limited and quenched by transfer into an ICT state. The fast LE fluorescence component varies systematically with conjugation length for the series of D–B–A dyads 2 – 5 . An attenuation factor β of 0.15 Å^?1 was determined in accordance with an ICT superexchange mechanism.     

Investigation of spacer influences in phosphorescent‐emitting nonconjugated PLED systems

An assay was introduced to clarify influences on electroluminescent behavior for RGB‐colored phosphorescent terpolymers with N,N‐Di‐p‐tolyl‐aniline as hole‐transporting unit, 2‐(4‐biphenyl)‐5‐(4‐tert‐butylphenyl)‐1,3,4‐oxadiazole (tert‐BuPBD) as electron‐transporting unit, and different iridium complexes in RGB‐colors as triplet emitting materials. All monomers were attached with spacer moieties to the “para” position of a polystyrene. Polymer light emitting diodes (PLEDs) were built to study the electro‐optical behavior of these materials. The gist was a remarkable influence of hexyl‐spacer units to the PLED performance. For all three colors only very restricted PLED performances were found. In comparison RGB‐terpolymers were synthesized with directly attached charge transport materials to the polymer backbone. For this directly linked systems efficiencies were 28 cd A^?1 @ 6 V (green), 4.9 cd A^?1 @ 5 V (red) and 4.3 cd A^?1 @ 6 V (bluish). In summary we assume that an improved charge percolation pathways regarding to the higher content of semiconducting molecules and an improved charge transfer to the phosphorescent dopand in the case of the copolymers without spacers are responsible for the better device performance comparing the copolymers with hexyl spacers. The approach of the directly connected charge transport materials at the nonconjugated styrene polymer backbone should be favored for further investigations, therefore. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 389–402, 2010