A new electrochromic copolymer based on dithienylpyrrole and EDOT

A new compound, namely diethyl 2,5-di(thiophen-2-yl)-1H-pyrrole-3,4-dicarboxylate (1), was copolymerized with 3,4-ethylenedioxythiophene (EDOT) via electrochemical method. The copolymer exhibits multicolor electrochromic property: It is found that the copolymer, poly(1-co-EDOT), has a specific optical band gap (1.71 eV) to reflect and/or transmit reddish brown color in the neutral state, and it can be switched to reddish orange, orange, yellowish green and blue colors upon oxidation in a low switching time (1.0 s). Importantly, these colors are essential for camouflage and/or full color electrochromic device/display applications. In addition to these, the obtained copolymer has a coloration efficiency of 173 cm²/C at 500 nm.     

Donor acceptor type neutral state green polymer bearing pyrrole as the donor unit

A new neutral state green polymer, poly (2,3-bis(4-tert-butylphenyl)-5,8-di(1H-pyrrol-2-yl) quinoxaline) (PTBPPQ) was synthesized and its potential use as an electrochromic material was investigated. Spectroelectrochemistry studies showed that polymer reveals two distinct absorption bands as expected for a donor–acceptor type polymer, at 408 and 745 nm. In addition, polymer has excellent switching properties with satisfactory optical contrasts and very short switching times. Outstanding optical contrast in the NIR region and stability make this polymer a great candidate for many applications. It should be noted that PTBPPQ is one of the few examples of neutral state green polymeric materials with superior switching properties. Hence, PTBPPQ can be used as a green polymeric material for display technologies.     

Efficient blue organic light-emitting diodes based on triphenylimidazole substituted anthracene derivatives

A series of new blue emissive materials based on the conjugates of highly fluorescent diaryl anthracene and electron-transporting triphenylimidazole moieties: 2-(4-(anthracen-9-yl)phenyl)-1,4,5-triphenyl-1H-imidazole (ACBI), 2-(4-(10-(naphthalen-1-yl)anthracen-9-yl)phenyl)-1,4,5-triphenyl-1H-imidazole (1-NaCBI), 2-(4-(10-(naphthalen-2-yl)anthracen-9-yl)phenyl)-1,4,5-triphenyl-1H-imidazole (2-NaCBI) were designed and synthesized successfully. These materials exhibit good film-forming properties and excellent thermal stabilities. Meanwhile, the decreased π-conjugation in these compounds compared with phenanthroimidazole derivatives leads to obvious hypsochromic shift. To explore the electroluminescence properties of these materials, typical three-layer organic light-emitting devices were fabricated. With respect to the three layer device 2 using 1-NaCBI as the emitting layer, its maximum current efficiency reaches 3.06 cd A⁻¹ with Commission Internationale del’Eclairage (CIE) coordinates of (0.149, 0.092). More interestingly, sky blue doped device 5 based on 1-NaCBI achieved a maximum current efficiency of 15.53 cd A⁻¹ and a maximum external quantum efficiency of 8.15%, high EQE has been proved to be induced by the up-conversion of a triplet excited state.     

Molecular design of large-bandgap host materials and their application to blue phosphorescent organic light-emitting diodes

New large-bandgap host materials with carbazole and carboline moieties were designed and synthesized for high-performance blue phosphorescent organic light-emitting diodes (PhOLEDs). The two kinds of host materials, 9-(4-(9H-carbazol-9-yl)phenyl)-6-(9H-carbazol-9-yl)-9H-pyrido[2,3-b]indole (pP2CZCB) and 9-(3-(9H-carbazol-9-yl)phenyl)-6-(9H-carbazol-9-yl)-9H-pyrido[2,3-b]indole (mP2CZCB), displayed promisingly high triplet energies of ∼2.92–2.93 eV for enhancing the exothermic energy transfer to bis[2-(4,6-difluorophenyl)pyridinato-C²,N](picolinato)iridium(III) (FIrpic) in PhOLED devices. It was found that the blue PhOLEDs bearing the new host materials and the FIrpic dopant exhibited markedly higher external quantum efficiencies (EQEs) than a device made with 1,3-bis(N-carbazolyl)benzene (mCP) as the host. In particular, the PhOLED device made with 3 wt% FIrpic as the dopant and mP2CZCB as the host material displayed a low driving voltage of 4.13 V and the high EQE of 25.3% at 1000 cd m⁻².     

Photoluminescent and electroluminescent properties and ultra-fast spectrometric studies of dihydroheptacenes

Photophysical and electrochemical properties of 7,16-dihydroheptacenes (1–3) were investigated in detail. Although their HOMO–LUMO gaps are higher than 3 eV, the organic light-emitting diodes containing 1 as the emitting dopant showed green electroluminescence (λ_max ∼ 515 and 550 nm) even at a concentration of the dopant as low as 1%. The green electroluminescence of 1 appears to be originating from an electromeric state (an intermolecular ion pair). The maximum brightness of 190 cd/m² was observed at a current density of 34 mA/cm² at operating voltage of 19 V for the device containing 1% 1, and overall performance of the devices decreased with an increase in the doping concentration of 1.     

Extremely low driving voltage electrophosphorescent green organic light-emitting diodes based on a host material with small singlet–triplet exchange energy without p- or n-doping layer

In order to achieve low driving voltage, electrophosphorescent green organic light-emitting diodes (OLEDs) based on a host material with small energy gap between the lowest excited singlet state and the lowest excited triplet state (ΔE_ST) have been fabricated. 2-biphenyl-4,6-bis(12-phenylindolo[2,3-a] carbazole-11-yl)- 1,3,5-triazine (PIC–TRZ) with ΔE_ST of only 0.11 eV has been found to be bipolar and used as the host for green OLEDs based on tris(2-phenylpyridinato) iridium(III) (Ir(ppy)₃). A very low onset voltage of 2.19 V is achieved in devices without p- or n-doping. Maximum current and power efficiencies are 68 cd/A and 60 lm/W, respectively, and no significant roll-off of current efficiency (58 cd/A at 1000 cd/m² and 62 cd/A at 10,000 cd/m²) have been observed. The small roll-off is due to the improved charge balance and the wide charge recombination zone in the emissive layer.     

Fluorene trimers with various 9,9′-substituents: The synthesis,characteristics, condensed state structures,and electroluminescence properties

The four fluorene-based trimers with various aromatic and alkyl substituents (T1–T4) are synthesized and characterized. These oligomers show the similar electronic absorption and emission characteristics (e.g., absorption peak at 351 nm, and highly efficient deep blue emission at 394 nm in solution), indicating that the major electronic properties of the core chromophore are essentially independent of the substituents. However, the condensed state structures and thermal properties of four trimers are found to be different from each other, from crystalline (full alkyl (T1) or full aromatic (T2) substituted trimers) to amorphous (mixed aromatic and alkyl (T4) substituted trimers). The effect of different condensed state structures on electroluminescence device properties is presented: The blue light-emitting devices with accordant structure of ITO/PEDOT:PSS/TCTA (40 nm)/trimers (40 nm)/BCP (10 nm)/Alq₃ (20 nm)/LiF/Al exhibit different EL efficiency (2.9% of T2, 1.8% of T3 and 2.7% of T4). Using amorphous T4, the white light-emitting device of ITO/TCTA (40 nm)/rubrene (0.1 nm)/T4 (8 nm)/Alq₃(52 nm)/LiF/Al is fabricated with high efficiency (6.15 cd A⁻¹), high brightness (9500 cd m⁻²) and good white light CIE coordinates (0.32, 0.37).     

Tetrasubstituted adamantane derivatives with arylamine groups: Solution-processable hole-transporting and host materials with high triplet energy and good thermal stability for organic light-emitting devices

Four new host/hole-transporting materials, namely 4,4′,4″,4‴-(adamantane-1,3,5,7-tetrayl)tetrakis(N,N-diphenylaniline) (4TPA-Ad, 1),4,4′,4″,4‴-(adamantane-1,3,5,7-tetrayl)tetrakis(N,N-di-p-tolylaniline) (4MTPA-Ad, 2), 1,3,5,7-tetrakis(4-(9H-carbazol-9-yl)phenyl)adamantane (4Cz-Ad, 3) and 1,3,5,7-tetrakis(4-(3,6-di-tert-butyl-9H-carbazol-9-yl)phenyl)adamantane (4tBuCz-Ad, 4), were designed and synthesized by incorporating four electron-donating arylamine units into the rigid adamantane skeleton via a simple C–N coupling reaction. Their thermal, photophysical and electrochemical properties were investigated. The molecular design endows the materials with high triplet energies of ∼3.0 eV, good solution processability, high thermal stability and appropriate HOMO levels. Two types of electroluminescent devices using 1–4 as hole-transporting or host materials were fabricated. The device based on 2 as solution-processed hole-transporting material and tris(quinolin-8-yloxy)aluminum as an emitter revealed a maximum current efficiency of 4.2 cd A⁻¹, which was comparable with the TAPC-based control device. The sky-blue device employing 2 as solution-processed host material and 4,6-(difluorophenyl)pyridine-N,C^2′)picolinate (FIrpic) as an emitter showed a maximum current efficiency of 16.6 cd A⁻¹ with Commission Internationale de I’Eclairage (CIE) coordinates of (0.16, 0.32).     

Molecular orientation of a new anthracene derivative for highly-efficient blue fluorescence OLEDs

A new anthracene derivative of 9,10-bis(2,5-dimethyl-4-(naphthalen-2-yl)phenyl)-2,3-diphenylanthracene (BDNPA) was designed and synthesized as a non-doped blue emitter in organic light emitting diodes (OLEDs). BDNPA has highly rigid structure and thermal stability with decomposition temperature (corresponding to 5% weight loss) of 490 °C, because p-naphthyl xylene groups in 9,10-positions were highly twisted to anthracene core due to steric hindrance of xylene groups, and because the 2,3-diphenyl groups were also twisted about 45–49° to anthracene. OLEDs with BDNPA non-doped emitter showed high efficiency of 5.21 cd/A due to the carrier mobility with well-aligned π-stacking structure toward out-of-plane by the face-on orientation by grazing incidence X-ray diffraction.     

Morphological study of polymer/fullerene interfaces via benzene–PC70BM interaction

We designed and synthesized a series of highly soluble random copolymers (P(BDTT-PhC8TPD-TPD)) comprising a two-dimensional (2D) electron-rich 2-ethylhexylthiophene-substituted benzo[1,2-b:4,5-b′]dithiophene (M1) electron-rich unit and various ratios of two side chain-functionalized thieno[3,4-c]-pyrrole-4,6-diones (M2 and M3) as planar electron-deficient units. The morphologies and photovoltaic performances of the bulk heterojunction blend films were examined, revealing concentration-dependent competitive benzene–benzene and benzene–fullerene interactions. A bulk heterojunction solar cell prepared using 10 mol% M2 (RP1) and PC₇₀BM exhibited a power conversion efficiency (PCE) of 4.9%, representing a significant improvement over the PCE (1.1%) obtained from parent copolymer (P1). The PCE in these cells was strongly associated with the nanoscale morphology of the BHJ film, which depended on the higher miscibility of RP1 with PC₇₀BM compared to RP2 (M2: 20 mol%), and RP3 (M2: 30 mol%).     

Synthesis and characterization of the conjugated polymers tethered with dipolar side chains containing a benzothiadiazole entity for bulk heterojunction solar cells

New conjugated copolymers (P1?P3) containing dipolar side chains connected to the main chain via triphenylamine donors have been synthesized and characterized. The side chains of these polymers have an electron deficient benzothiadiazole moiety in the spacer, but with different acceptors at the end. By changing the acceptor moieties of the side chain, the absorption spectra and HOMO/LUMO gaps of the polymers can be fine-tuned, ranging from 1.86 to 1.59 eV. Solution processed bulk heterojunction (BHJ) solar cells using these polymers as the donor and [6,6]-phenyl-C₆₁-butyric acid methyl ester (PCBM) as the acceptor were fabricated and measured under 100 mW cm^?2 of AM 1.5 illumination. The cell based on the blend of P1/PCBM (1:1, w/w) exhibited the highest power conversion efficiency of 1.78%, with open circuit voltage (V_oc) = 0.79 V, short circuit current (J_sc) = 6.63 mA cm^?2 and fill factor (FF) = 0.34, respectively.     

Synthesis and optoelectronic properties of a series of novel spirobifluorene derivatives starting from the readily available reagent 4,4′-bisalkylated biphenyl

Five novel spirobifluorene derivatives, SPF-DM, SPF-MB, SPF-BB, BSPF-NA1 and BSPF-NA2 were synthesized starting from the readily available reagent 4,4′-bisalkylated biphenyl. Their linear absorption, fluorescence and thermal properties were examined and their redox potential levels were estimated by cyclic voltammetry. These compounds possess high thermal stability. SPF-MB and SPF-BB possess excellent spectral sensitivities to pH changes and can be used as optical pH sensors of a wide pH range. The recognition behavior of SPF-BB toward various metal ions has been evaluated in a acetonitrile/water (15:1, v/v) solvent system. SPF-BB is highly selective in recognizing Ag⁺. The electroluminescent properties of SPF-DM, SPF-MB, BSPF-NA1 and BSPF-NA2 are demonstrated with a device configuration of ITO/MoO₃ (6 nm)/NPB (80 nm)/EML (30 nm)/TPBI (40 nm)/LiF (1 nm)/Al (100 nm). The devices of BSPF-NA1 and BSPF-NA2 display a yellow emission in the EL spectra and their maximum brightness reached 380 and 311 cd m^?2, respectively. At low turn-on voltage (7.9 V) a light blue emission was observed in the device of SPF-DM and its maximum brightness reached 391 cd m^?2. Notably, the device of SPF-MB has a white emission with CIE coordinates (0.293, 0.307).     

Effects on the electrochemical and electrochromic properties of 3,6 linked polycarbazole derivative by the introduction of different acceptor groups and copolymerization

Two novel donor–acceptor type monomers, ethyl 4-(3,6-di(thiophen-2-yl)-9H-carbazole-9-yl)-benzoate (ETCB) and 9-(4-nitrophenyl)-3,6-di(thiophen-2-yl)-9H-carbazole (NDTC), were synthesized and characterized. Both the monomers show good electrochemical activity. UV–vis absorption studies reveal that the spectra of them are obviously different due to the introduction of the acceptor groups with different polarity, and the compound with –NO₂ group has lower band gap. Fluorescent spectral studies indicate that the solution of ETCB in DCM exhibits sky-blue emission, while the NDTC hardly displays the fluorescence because of stronger intramolecular charge transfer. Their polymers can be synthesized by electropolymerization, and both the films show well-defined oxidation and reduction process. Spectroelectrochemical analysis reveals that PETCB film displays the color change from yellow–green (neutral) to blue–purple (oxidized), while the color change of PNDTC film is from yellow (neutral) to gray (oxidized). Both the polymer films exhibit reasonable optical contrast and switching time. Moreover, the copolymer based on ETCB and 3,4-ethylenedioxythiophene (EDOT) is also investigated. The copolymer could show five colors change under different applied potentials and higher optical contrast (50% of 1100 nm) and coloration efficiency (356.88 cm² C^?1).     

Novel ruthenium sensitizer with multiple butadiene equivalent thienyls as conjugation on ancillary ligand for dye-sensitized solar cells

A heteroleptic polypyridyl ruthenium complex ‘cis-Ru(4,4′-bis(3,5-bis(5-hexylthiophen-2-yl)phenyl)-2,2′-bipyridine)(4,4′-dicarboxyl-2,2′-bipyridine) (NCS)₂, MC102′, with a high molar extinction coefficient was synthesized and characterized with IR, ¹H NMR, Mass, UV–Vis spectroscopy. The test cell DSSC devices constructed with 0.23 cm² active area photo-electrode in combination with an electrolyte composed of 0.6 M dimethylpropyl-imidazolium iodide (DMPII), 0.05 M I₂, and 0.1 M LiI in acetonitrile yielded solar to electric energy conversion efficiency (η) of 4.42% under Air Mass (AM) 1.5 sunlight, while the reference N719 sensitized solar cell fabricated and evaluated under similar conditions exhibited η-value of 5.84%.     

Molecular modification on bisphenanthroimidazole derivative for deep-blue organic electroluminescent material with ambipolar property and high performance

Efficient deep-blue fluorescent emitters are of particular significance in organic light-emitting devices (OLEDs). An ambipolar deep-blue emitter, 4,4′-bis(4-(1-(4-(tert-butyl)phenyl)-1H-phenanthro[9,10-d]imidazol-2-yl)phenyl)-1,1′-binaphthalene (2NBTPI), was designed, synthesized and applied in a high-efficiency deep-blue emitting OLED. By modifying with binaphthyl, 2NBTPI exhibits a high thermal stability, deep blue emission as well as spatially separated HOMO and LUMO orbits. Comparing with its mononaphthyl counterpart 1,4-bis(4-(1-(4-(tert-butyl)phenyl)-1H-phenanthro[9,10-d]imidazol-2-yl)phenyl)naphthalene (NBTPI), 2NBTPI shows more balanced charge transport properties, better color purity (color index: (0.15, 0.09) versus (0.15, 0.11)), higher external quantum efficiency (EQE) (5.95% versus 5.73%) and slower efficiency roll-off (EQE roll-off at 100 mA cm⁻²: 13.1% versus 27.6%). To the best of our knowledge, OLED performances of 2NBTPI are comparable to the best reported non-doped deep-blue emitters.     

A highly efficient OLED based on terbium complexes

A neutral ligand 9-(4-tert-butylphenyl)-3,6-bis(diphenylphosphineoxide)-carbazole (DPPOC) and its complex Tb(PMIP)₃DPPOC (A, where PMIP stands for 1-phenyl-3-methyl-4-isobutyryl-5-pyrazolone) were synthesized. DPPOC has a suitable lowest triplet energy level (24,691 cm^?1) for the sensitization of Tb(III) (⁵D₄: 20,400 cm^?1) and a significantly higher thermal stability (glass transition temperature 137 °C) compared with the familiar ligand triphenylphosphine oxide (TPPO). Experiments revealed that the emission layer of the Tb(PMIP)₃DPPOC film could be prepared by vacuum co-deposition of the complex Tb(PMIP)₃(H₂O)₂ (B) and DPPOC (molar ratio = 1:1). The electroluminescent (EL) device ITO/N,N′-diphenyl-N,N′-bis(1-naphthyl)-1,1′-diphenyl-4,4′-diamine (NPB; 10 nm)/Tb(PMIP)₃ (20 nm)/co-deposited Tb(PMIP)₃DPPOC (30 nm)/2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP; 10 nm)/tris(8-hydroxyquinoline) (AlQ; 20 nm)/Mg_0.9Ag_0.1 (200 nm)/Ag (80 nm) exhibited pure emission from terbium ions, even at the highest current density. The highest efficiency obtained was 16.1 lm W^?1, 36.0 cd A^?1 at 6 V. At a practical brightness of 119 cd m^?2 (11 V) the efficiency remained above 4.5 lm W^?1, 15.7 cd A^?1. These values are a significant improvement over the previously reported Tb(PMIP)₃(TPPO)₂ (C).     

A new p- and n-dopable selenophene derivative and its electrochromic properties

A novel electrically conducting polymer, poly(2-dodecyl-4,7-di(selenophen-2-yl)benzotriazole) (PSBT), containing selenophene as the strong donor and benzotriazole as the strong acceptor groups was synthesized by electrochemical polymerization. Homopolymerization and copolymerization (in the presence of 3,4-ethylenedioxythiophene (EDOT)) were achieved in acetonitrile/dichloromethane(95/5 v/v) with 0.1 M tetrabutylammonium hexafluorophosphate (TBAPF₆). The electrochemical and optical properties of homopolymer and copolymer were investigated by cyclic voltammetry, UV–Vis, near IR Spectroscopy. Cyclic voltammetry and spectroelectrochemistry studies demonstrated that homopolymer can be reversibly reduced and oxidized (both n- and p-doped) between ?1.9 V and +1.4 V, at a scan rate of 100 mV/s. The homopolymer revealed a transmissive light blue color in the oxidized state, and a red-purple color in the neutral state. A transmissive light blue color was also observed in the reduced state. Homopolymer films could be fully switched between their reduced and oxidized forms in 2.4 s and 0.4 s with a percent transmittance of 32% and 56% at 511 and 1200 nm, respectively. Poly(SBT) exhibits a λ_max value of 511 nm and a band gap of 1.67 eV which is quite low among the selenophene-containing polymers reported so far except for poly(1,2-bis(2-seleninyl)ethane).     

Synthesis,optical and electrochemical properties of pyridal[2,1,3]thiadiazole based organic dyes for dye sensitized solar cells

The asymmetric nature of pyridal[2,1,3]thiadiazole (PyT), allows the synthesis of two isomers, series SC-PyTNn (n = 1–4) and SC-NPyTn (n = 1–6), where the nitrogen atom of PyT is positioned closer to the arylamine donor and the anchoring group, respectively. PyT derivatives have significant bathochromic shift of the electronic absorption compared to their 2,1,3-benzothiadiazole congeners. The short-circuit photocurrent density, open-circuit voltage and fill factor of DSSCs using the dyes as the sensitizers are in the range of 0.68–9.47 mA/cm⁻², 0.43–0.61 V and 0.59–0.72, respectively. SC-NPyTn (n = 1–6) exhibited higher cell efficiencies than SC-PyTNn (n = 1–4). Power conversion efficiency of up to 4.24% was observed for SC-NPyT3.     

High efficiency yellowish green phosphorescent emitter derived from phenylbenzothienopyridine ligand

A yellowish green phosphorescent dopant derived from phenylbenzothienopyridine ligand, iridium (III) [bis(1-phenylbenzo[4,5]thieno[2,3-c]pyridinato-N,C²]picolinate. (Ir(DTNP)₂pic) was synthesized and the device performances of the Ir(DTNP)₂pic was studied. The Ir(DTNP)₂pic dopant exhibited yellowish green emission at 548 nm and showed a high quantum efficiency of 22.4% at 1000 cd/m² with a color coordinate of (0.43, 0.57) in yellowish green phosphorescent organic light-emitting diodes.     

Highly efficient single-layer organic light-emitting devices using cationic iridium complex as host

Highly efficient single-layer organic light-emitting devices (OLEDs) based on blended cationic Ir complexes as emitting layer have been demonstrated using narrow band gap cationic Ir complex [Ir(Meppy)₂(pybm)](PF₆) (C1) as guest and wide band gap cationic Ir complex [Ir(dfppy)₂(tzpy-cn)](PF₆) (C2) as host. As compared with single cationic Ir complex emitting layer, these host–guest systems exhibit highly enhanced efficiencies, with maximum luminous efficiency of 25.7 cd/A, external quantum efficiency of 8.6%, which are nearly 3-folds of those of pure C1-based device. Compared with a multilayer host-free device containing C1 as emitting layer and TPBI as electron-transporting and hole-blocking layer, the above single-layer devices also show 2-folds enhancement efficiencies. The high efficiencies achieved in these host–guest systems are among the highest values reported for ionic Ir complexes-based solid-state light-emitting devices. In addition, a white-similar emission with CIE of (0.36, 0.47) has also been achieved with luminous efficiency of 4.2 cd/A as the C1 concentration is 0.1 wt.%. The results demonstrate that the ionic Ir complexes-based host–guest system provides a new approach to achieve highly efficient OLEDs upon single-layer device structure and solution-processing technique.