Based on a carbazole-functionalized polyspirobifluorene with high fluorescence quantum yield and deep-blue emission, a series of blue-, green-, and red-emitting polymers have been successfully developed by independently incorporating dibenzothiophene-S,S-dioxide (3,7SO), 4,7-diphenylbenzothiadiazole (DPBT), and 4,7-dithienylbenzothiadiazole (DTBT) as the copolymerized units to tune the emission color in the whole visible region. The effect of their loadings on the electrochemical, photophysical, and electroluminescent properties is investigated in detail. It is found that PCzSF-3,7SO15, PCzSF-DPBT15, and PCzSF-DTBT03 show the best blue, green, and red device performance, revealing state-of-the-art luminous efficiencies of 5.6, 21.6, and 4.4 cd A–1 along with CIE coordinates of (0.16, 0.16), (0.32, 0.60), and (0.61, 0.34), respectively. The results clearly indicate that the carbazole-functionalized polyspirobifluorene is a promising platform to construct high-efficiency multicolor polymers suitable for PLEDs.

Two new furo[3,2-c]pyridine-based Ir complexes, namely (4-MeOpfupy)2Ir(acac) and (3-MeOpfupy)2Ir(acac), were designed and synthesized by introducing a methoxyl group into the 4- and 3-positions of the phenyl ring on the C^N ligand. It was found that the position of the methoxyl group has an important influence on the electrochemical and photophysical properties, as well as electrophosphorescent device performance. Compared with the reference complex (pfupy)2Ir(acac) without any methoxyl group (538 nm), (4-MeOpfupy)2Ir(acac) with a methoxyl group at the 4-position shows a blue-shifted emission peak at 523 nm originating from the methoxyl-induced enhancement of the LUMO level, whereas (3-MeOpfupy)2Ir(acac) with a methoxyl group at the 3-position shows a red-shifted emission peak at 602 nm originating from the methoxyl-induced enhancement of the HOMO level. The corresponding PhOLEDs based on (4-MeOpfupy)2Ir(acac) and (3-MeOpfupy)2Ir(acac) realize highly efficient green and orange electroluminescence with CIE coordinates of (0.37, 0.60) and (0.60, 0.40), revealing a state-of-the-art EQE as high as 29.5% (100.7 cd A−1) and 16.7% (43.9 cd A−1), respectively. These impressive results indicate that methoxyl modification is a valid way to tune the molecular energy levels and emissive color for Ir complexes while not obviously sacrificing the final device performance.

Solution processable red Ir dendrimers named R-D1, R-D2 and R-D3, which contain a quinoline-based homoleptic complex as the core and oligocarbazole as the dendron, have been facilely and successfully designed and synthesized via a post-dendronization procedure. With the increasing dendron generation from R-D1 to R-D3, the intermolecular interactions and luminescence quenching in solid states are found to be effectively prevented because of encapsulation from the outer dendrons. As a result, the third-generation dendrimer R-D3 achieves the best nondoped device performance, revealing a promising EQE of 10.5% (9.2 cd A−1, 7.0 lm W−1) with CIE coordinates of (0.67, 0.33). Furthermore, the doped devices of R-D3 show a wide doping concentration window in the range of 5–30 wt%, and a maximum EQE as high as 18.3% (25.7 cd A−1, 33.0 lm W−1) is realized at about a 10 wt% doping content. The results can compete well with vacuum-deposited small molecular red phosphors, representing important progress on solution processable phosphorescent dendrimers with red emission.

A solution-dispersible hyperbranched conjugated polymer nanoparticle material based on triazatruxene, TATHBP-DCV, was readily prepared through Suzuki coupling polymerization in a miniemulsion, followed by post-functionalization of its numerous terminal aldehyde groups into dicyanovinyl groups. Efficient energy transfer from the polymer core to the peripheral terminal units quenched the emission of TATHBP-DCV, which was turned on in hydrazine vapor. In particular, fluorescence fiber-optic detection of hydrazine vapor was realized with a limit of detection down to 1.1 mg m−3 in 5 minutes.

For solution processability of polymer solar cells (PSCs), polymer electron donors are almost always composed of conjugated main chains and flexible alkyl side chains. In this paper, we report a polymer electron donor based on isoindigo units bearing branched oligo(ethylene glycol) (OEG) side chains, P-OEG. Compared with the control polymer bearing alkyl side chains (P-Alkyl), P-OEG exhibits not only a smaller π–π stacking distance and redshifted absorption spectra, but also larger surface energy for better compatibility with the [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) electron acceptor. The PSC device of P-OEG exhibits an open-circuit voltage (VOC) of 0.73 V, short-circuit current density (JSC) of 13.92 mA cm−2, and fill factor (FF) of 0.50, corresponding to the power conversion efficiency (PCE) of 5.10%. This performance is higher than that of P-Alkyl (PCE = 3.0%), which is attributed to the finer phase separation morphology of the P-OEG:PC71BM blend than that of the P-Alkyl:PC71BM blend. These results suggest that the branched OEG side chain is an effective approach to improve the PSC device performance of some polymer electron donors.

AbstractSolution-processed phosphorescent white organic light-emitting diodes (WOLEDs) with improved power efficiency are reported by simply blending a yellow phosphor Ir(Flpy-CF3)3 into a self-host blue Ir dendrimer B-G2. Attributable to the elimination of the host-induced power efficiency losses existed in the traditional host-based devices, a state-of-the-art total power efficiency as high as 48.8–62.8 lm W−1 is achieved at a practical luminance of 1000 cd m−2. Moreover, without considerably sacrificing the power efficiency, the related correlated color temperature and Commission Internationale de L'Eclairage coordinates can be well tuned to satisfy different illumination requirements. The results clearly demonstrate that the adoption of a self-host blue phosphorescent dendrimer instead of the traditional host-based device structure is a superior and promising strategy to realize power-efficient white-light emitting devices.

Dendron engineering in self-host blue Ir dendrimers is reported to develop power-efficient nondoped electrophosphorescent devices for the first time, which can be operated at low voltage close to the theoretical limit (Eg/e: corresponding to the optical bandgap divided by the electron charge). With increasing dendron's HOMO energy levels from B-POCz to B-CzCz and B-CzTA, effective hole injection is favored to promote exciton formation, resulting in a significant reduction of driving voltage and improvement of power efficiency. Consequently, the nondoped device of B-CzTA achieves extremely low driving voltages of 2.7/3.4/4.4 V and record high power efficiencies of 30.3/24.4/16.3 lm W−1 at 1, 100 and 1000 cd m−2, respectively. We believe that this work will pave the way to the design of novel power-efficient self-host blue phosphorescent dendrimers used for energy-saving displays and solid-state lightings.

By fully replacing the alkyloxy side chain with a carbazole, we have designed and synthesized a highly emissive carbazole-functionalized homopoly(spirobifluorene) (denoted as P(Cz-SF)) for deep-blue polymer light-emitting diodes (PLEDs). Attributable to such a small variation of the molecular structure, the unwanted charge transfer from the pendant to the backbone can be effectively prevented in P(Cz-SF). Compared with the alkyloxy-tethered polymer P(RO-SF) (λPL = 455 nm, FWHM = 58 nm, ΦPL = 0.20), P(Cz-SF) shows a blue-shifted emission of 422 nm accompanied by a narrower full width at half maximum (FWHM) of 45 nm and an improved photoluminescence quantum yield (PLQY) of 0.60 in solid films. As a consequence, a high-performance deep-blue device is realized for P(Cz-SF), revealing a state-of-the-art external quantum efficiency of 3.0% associated with Commission Internationale de L'Eclairage (CIE) coordinates of (0.17, 0.06). The results indicate that poly(spirobifluorene) with a carbazole as the side chain instead of alkyloxy will be a promising platform to develop efficient deep-blue emitters used for PLEDs.

A novel furo[3,2-c]pyridine based Ir complex, namely (pfupy)2Ir(acac), has been developed by replacing sulfur with oxygen in the C^N ligand. Compared with the thiophene-containing (pthpy)2Ir(acac), the LUMO level is elevated while the HOMO level remains almost unchanged for the resultant furan-containing (pfupy)2Ir(acac). As a consequence, the emissive maximum is blue-shifted from 556 nm of (pthpy)2Ir(acac) to 538 nm of (pfupy)2Ir(acac) together with an improved photoluminescence quantum yield of 0.80. The corresponding device based on (pfupy)2Ir(acac) realizes a record-high external quantum efficiency (EQE) of 30.5% (110.5 cd A−1) without any out-coupling technology. Even at a luminance of 1000 and 5000 cd m−2, the EQE still remains at 26.6% (96.4 cd A−1) and 25.6% (92.7 cd A−1), respectively, indicative of the gentle efficiency roll-off. The results clearly demonstrate the great potential of furan-based functional materials applied in OLEDs.

Self-host Ir dendrimers have been adopted as the nondoped emitting layer for the successful construction of multilayer green phosphorescent organic light-emitting diodes (PhOLEDs) prepared via layer-by-layer solution processing with orthogonal solvents. Unlike previous doped systems, the risk of small-molecular-phosphor redissolution by alcohols and the resultant serious batch-to-batch variation can be eliminated. Consequently, a record-high external quantum efficiency of 21.2% together with good reproducibility is achieved for the green-emitting Ir dendrimer G2, which displays sufficient alcohol resistance owing to the effective encapsulation from the second generation dendritic wedge. The obtained performance is highly competitive with those of doped devices, while avoiding the unwanted redissolution-induced batch-to-batch variation simultaneously, representing an important development in the solution fabrication of multilayer PhOLEDs based on a nondoped system.

A novel self-host red Ir dendrimer D-(PPQ)2Ir(acac) has been developed for solution-processed nondoped phosphorescent organic light-emitting diodes (PhOLEDs) by fully encapsulating the heteroleptic complex (PPQ)2Ir(acac) with oligocarbazole at both the C∧N and O∧O ligands. Due to the shielding effect of the dendritic wedge, the intermolecular interactions and luminescence quenching are found to be significantly reduced from (PPQ)2Ir(acac) to D-(PPQ)2Ir(acac). Correspondingly, the maximum external quantum efficiency (EQE) of hybrid-solution-processed electrophosphorescent devices is increased from 0.5% to 9.9%. Moreover, D-(PPQ)2Ir(acac) shows a good alcohol resistance in the presence of the large-size carbazole dendrons. Such a feature does favor the successful fabrication of all-solution-processed devices via an orthogonal solvent processing, revealing an optimized EQE as high as 11.1% (8.7 cd A−1, 6.0 lm W−1) with CIE coordinates of (0.67, 0.33). The results indicate that highly efficient solution-processed red-emitting nondoped PhOLEDs with over 10% EQE can also be realized based on a self-host phosphorescent dendrimer system.

A novel self-host blue-emitting iridium dendrimer, namely, B-CzPO, has been designed and synthesized via a postdendronization route, where a bipolar carbazole/triphenylphosphine oxide hybrid is selected as the peripheral dendron instead of the p-type oligocarbazole used in unipolar analogue B-CzG2. This structural modification can render B-CzPO with more balanced charge transportation relative to that of B-CzG2. As a result of the significantly reduced efficiency roll-off, the nondoped phosphorescent organic light-emitting diodes (PhOLEDs) of B-CzPO show a superior high-brightness performance, revealing a luminous efficiency of 21.2, 16.1, and 10.5 cd/A at 1000, 5000, and 10 000 cd/m2, respectively. Compared with that of B-CzG2 (i.e., 7.8 cd/A @5000 cd/m2), more than doubled high-brightness performance is achieved for B-CzPO. The results indicate that the design of self-host phosphorescent dendrimers with a bipolar feature will be a promising strategy to develop efficient nondoped PhOLEDs suitable for high-brightness applications including general illumination and micro displays.Keywords: bipolar dendrons; high-brightness performance; iridium dendrimers; nondoped PhOLEDs; self-host

Two solution-dispersible hyperbranched conjugated polymer nanoparticles based on triazatruxene, TATF8HBP and TATSFHBP, have been prepared through Suzuki polymerization in a miniemulsion. They can be stably dispersed in common organic solvents. Blue emission of their spin-coated films could be efficiently quenched by DNT and TNT vapors. The steric hindrance of the spirobifluorene unit inside TATSFHBP endowed it with higher fluorescence quantum yield in solid film and better sensitivity toward nitroaromatic explosive vapors. Rapid, sensitive and reversible explosive fiber-optic detection with TATSFHBP has been demonstrated with fluorescence quenching efficiency up to 99% in just 15 s and 93% in 90 s after exposure to DNT and TNT vapors, respectively. TATSFHBP-coated indicating papers can visually detect trace TNT particulates with a low detection limit of 0.23 ng mm−2.

Bright blue light-emitting molecules based on triazatruxene have been prepared and used for nitroaromatic explosive vapor detection. The fiber-optic probe using a star-shaped carbazole-functionalized triazatruxene derivative (TATCz3) as the sensing material exhibits promising potential as an extremely fast-response and highly sensitive sensor for detection of TNT and DNT vapors.

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.Recent advances in using poly(arylene ether)s as light-emitting polymers, including fluorescent polymers, host polymers and phosphorescent polymers are overviewed.

On the basis of different generation carbazole dendrons, a series of self-host yellow Ir dendrimers (Y-G0, Y-G1 and Y-G2) have been successfully synthesized and characterized in detail. It is found that the peripheral dendrons can effectively reduce the intermolecular interactions between emissive Ir cores, as verified by the increased photoluminescence quantum yields and film lifetimes. Among these dendrimers, Y-G2 bearing the second generation dendrons shows the best non-doped device performance, revealing a peak luminous efficiency of 20.2 cd/A. The value is nearly twice that of Y-G0 without any dendrons, which could be further improved to 32.1 cd/A by dispersing Y-G2 into a host matrix. We believe that this work will shed light on the development of highly efficient yellow phosphorescent dendrimers with a self-host strategy.

On the basis of a well-known hole transporting material, namely 4,4′,4′′-tris(carbazol-9-yl)-triphenylamine (TCTA), a series of star-shaped deep-blue fluorescent emitters (2P-TCTA, 3P-TCTA, 4P-TCTA and 5P-TCTA) have been successfully developed via a simple extension of the oligophenyl chain between two N atoms. When the number of phenyl rings increases, it is found that both the absorption and emission for these TCTA-based starbursts are red-shifted and finally become saturated for 5P-TCTA consisting of a pentaphenyl bridge. Interestingly, on going from 2P-TCTA to 5P-TCTA, the film photoluminescence quantum yield is gradually enhanced from 11.4% to 35.5%. The same trend is also observed for their corresponding solution-processed undoped OLEDs. As a consequence, 5P-TCTA shows the best device performance, revealing a maximum luminescence of 7300 cd m−2, and a peak luminous efficiency of 2.48 cd A−1 (2.15 lm W−1; 2.30%) together with CIE coordinates of (0.15, 0.09).

A series of solution processible deep-blue fluorescent emitters TFPC0 ∼ TFPC2 have been designed and synthesized by incorporating different generation carbazole dendrons into the 9,9-positions of the terfluorene backbone. Compared with TFPC0, the dendritic TFPC1 and TFPC2 have the elevated glass transition temperatures as well as better solubility in common organic solvents, and their high quality amorphous films can be formed via spin-coating. Noticeably, with the increasing generation number, both the intermolecular aggregate and the formation of keto defects can be effectively suppressed to avoid the appearance of the unwanted long wavelength emission. Meanwhile, the highest occupied molecular orbital (HOMO) level is gradually enhanced from TFPC0 to TFPC2, facilitating the hole injection. As a result, TFPC2 with the second generation carbazole dendrons shows the best photoluminescence and electroluminescence stability among TFPC0 ∼ TFPC2. Its corresponding solution-processed undoped device gives a state-of-art external quantum efficiency as high as 2.02% and Commission International De L'Eclairge (CIE) coordinates of (0.16, 0.04). These results indicate that the introduction of oligocarbazole is a promising strategy towards solution processible deep-blue fluorene-containing oligomers simultaneously with high spectral stability and efficiency.

A facile synthesis has been demonstrated for the first time to construct self-host functional Ir-cored dendrimers up to the fourth generation on the basis of a newly developed polyether dendron, where the N-phenylcarbazole (NPC) moiety is used as the basic building block instead of benzene to improve charge transport whilst keeping the ease of preparation. With the growing generation number, the dendrimer size can be well tuned in a wide range of 4–10 nm. The obtained fourth generation dendrimer 45NPC-G4 is the largest Ir complex ever reported so far, having a diameter up to 10 nm and a molecular weight as high as 15.9 kDa. Most interestingly, the performance of non-doped phosphorescent organic light-emitting diodes (PhOLEDs) is found to be greatly dependent on the molecular size. For example, 9NPC-G2 (R ≈ 30 Å) reveals the best luminous efficiency as high as 50.5 cd A−1 (56.6 lm W−1, 14.8%), whereas the efficiency of 45NPC-G4 (R ≈ 50 Å) sharply drops to 10.5 cd A−1 (5.6 lm W−1, 3.4%). The results suggest that an appropriate size of 6 ± 2 nm is desirable to balance the dilemma between luminescence quenching and charge transport, and thereby realize highly efficient non-doped PhOLEDs.

Normal photovoltaic polymers must be processed with halogenated solvents, which are harmful to the environment and cannot be used for the mass production of polymer solar cells (PSCs). We report a novel approach to develop photovoltaic polymers suitable for non-halogenated solvent processing by attaching a polar and inert phosphonate moiety to the side chain of conventional photovoltaic polymers. The pendant phosphonate moiety does not obviously affect the electronic structure of the conjugated polymer backbone but greatly changes the solubility of the polymers. The phosphonated polymers are soluble in several polar non-halogenated solvents, such as methoxybenzene (MOB), methylbenzoate (MBz), o-dimethoxybenzene (o-DMOB), etc. PSCs of the phosphonated polymers processed with MOB exhibit better photovoltaic performances than those of the devices processed with common halogenated solvents. A power conversion efficiency (PCE) of 2.11% is achieved with the device processed with MOB, in comparison to the PCE of 0.90% with chlorobenzene (CB) as the processing solvent and the PCE of 1.59% with o-dichlorobenzene (o-DCB) as the processing solvent. These results indicate that a pendant phosphonate moiety is an effective approach to developing photovoltaic polymers towards the production of PSCs fabricated using environmentally friendly solvents.

Tuning fluorescence properties and frontier orbital energy levels of hyperbranched conjugated polymer nanoparticles (HCPN-NMe) by the facile introduction of terminal N,N-dimethylaniline groups via an intramolecular charge transfer (ICT) process between the nanoparticle core and the terminal groups was demonstrated for the first time. Compared with the similar hyperbranched conjugated polymer nanoparticles with terminal benzene groups (HCPN-H), a large Stokes shift and remarkable fluorescence solvatochromism were observed for HCPN-NMe. Based on the environmental-sensitive ICT emission, HCPN-NMe can be used as a fluorescence sensor for the detection of water in THF with enhanced sensitivity.

A series of solution processible greenish-blue-emitting Ir dendrimers with polyether dendrons that consist of N-phenylcarbazole (NPC) are developed via a convenient post-dendronization method. It involves two steps: (i) the successful preparation of a reactive Ir core, namely m-HO-dfppyIr, only when the hydroxyl group is located at the meta position relative to the N atom in the C^N ligand so as to eliminate the possible resonance structure between enol and keto; and (ii) the subsequent functionalization with NPC-based polyether dendrons to afford the first, second and third generation Ir dendrimers (Ir-G1B, Ir-G2B and Ir-G3B) with ease and high yields over 60%. All these dendritic complexes possess good thermal stability with decomposition temperatures higher than 380 °C and glass transition temperatures higher than 200 °C. In addition, with the growing generation number, the intermolecular interactions between emissive Ir cores are expected to be effectively inhibited to avoid the luminescence quenching, which is confirmed from the blue-shifted emission peak and the enhanced lifetime of Ir-G3B in the solid state. As a result, on going from Ir-G1B to Ir-G3B, the maximum luminous efficiency rises upward from 4.7 to 9.2 cd A−1 for nondoped electrophosphorescent devices. Further optimization by doping them into a dendritic H2 host leads to the improved luminous efficiencies as high as 20.0–25.2 cd A−1.

We synthesize and systematically study a series of conjugated polymers with oligo(ethylene glycol) (OEG) or alkyl chain as the side chain and poly[2,7-fluorene-alt-5,5-(4,7-di-2-thienyl-2,1,3-benzothiadiazole)] as the polymer backbone. Replacing alkyl chain with OEG chain can decrease the π–π stacking distance of polymer backbone in thin film from 0.44 to 0.41 nm because OEG chain is more flexible than alkyl chain. As the result, the conjugated polymer with OEG side chain exhibits higher hole mobility, red-shifted absorption spectrum in thin film and smaller bandgap than those of the conjugated polymer with alkyl side chain. With the increase of the length of OEG side chain, the resulting conjugated polymers exhibit unchanged π–π stacking distance and decreased hole mobility. Moreover, owing to the large polarity of OEG chain, OEG side chain makes the conjugated polymer suitable for polymer solar cell (PSC) devices processed with polar nonhalogenated solvent, methoxybenzene. A power conversion efficiency of 4.04% is demonstrated with the resulting PSC devices. This work provides the new insight into the effect of OEG side chain on conjugated polymer, which can be used in the molecular design of novel conjugated polymer materials with excellent optoelectronic device performance.

A selective and sensitive fluorescent nanoprobe based on hyperbranched conjugated polymer nanoparticles (HBCPN-DCV) for cyanide detection was developed. HBCPN-DCV was readily prepared by Suzuki coupling polymerization in a mini-emulsion, followed by post-functionalization of numerous terminal aldehyde groups into cyanide-responsive dicyanovinyl fluorophores on the particle surface. An efficient Förster resonance energy transfer from the HBCPN core to the peripheral dicyanovinyl dyes was achieved in HBCPN-DCV. Taking advantage of the amplified energy transfer, the fluorescent turn-off cyanide detection mode of its model compound (M-DCV) could be transformed into the turn-on and ratiometric detection mode of HBCPN-DCV, with a limit of detection down to 0.2 μM. Meanwhile, clear fluorescent colour change at a cyanide concentration as low as 2 μM could be observed by the naked eye. In addition, compared to M-DCV, HBCPN-DCV exhibits higher sensitivity and wider linear region.

A series of blue-emitting poly(spirobifluorene)s (PSFs), namely, Cz-PSF, 4RO-PSF and DPA-PSF, have been designed and synthesized by incorporating 2,7-bis(3,6-di-tert-butyl-9H-carbazol-9-yl)-9H-fluorene (CzF), 2,3,6,7-tetraoctyloxyfluorene (4ROF) and N,N′,N′′,N′′′-tetrakis(4-butylphenyl)-9H-fluorene-2,7-diamine (DPAF) as their electron-rich side chains, respectively. Consistent with their measured HOMO levels (CzF: −5.40 eV; 4ROF: −5.17 eV; DPAF: −4.86 eV), the donor strength of the pendant is enhanced in the sequence CzF < 4ROF < DPAF. As a result, the charge transfer (CT) effect from the pendant to the backbone is found to be gradually intensified on going from Cz-PSF to 4RO-PSF and DPA-PSF. The emission maximum is accordingly red-shifted from 423 nm for Cz-PSF to 452 nm for 4RO-PSF and 482 nm for DPA-PSF, which is associated with a significant decrease in the photoluminescent quantum yields. Compared with 4RO-PSF, the copolymer Cz-PSF containing a weaker donor shows deep-blue emission with CIE coordinates of (0.16, 0.09–0.12) and a peak luminous efficiency of 2.21 cd A−1. These results indicate that the CT effect can be effectively tuned to realize high-performance deep-blue-emitting PSFs by the manipulation of the electron-donating ability of their spiro-conjugated side chains.

Solution-dispersed porous hyperbranched conjugated polymer nanoparticles (PHCPN) were prepared via Suzuki polymerization in a toluene-in-water miniemulsion system. PHCPN with an average particle size of 40–120 nm can disperse in common organic solvents and show blue emission. PHCPN exhibit a much larger specific surface area (133 m2 g−1), compared with the analogues, hyperbranched conjugated polymer nanoparticles (HCPN, 13 m2 g−1) with octyl chains and a linear conjugated polymer (LCP, 0 m2 g−1). Moreover, PHCPN have enhanced sensitivity in both a THF dispersion and the solid state due to facile diffusion of TNT inside the porous conjugated polymer network structure. Especially, PHCPN-coated indicating papers can visually and reversibly detect trace TNT particulates with a low detection limit of 0.5 ng mm−2, which is about 20-fold more sensitive than that of the linear conjugated polymer (LCP).

Instead of conjugated dibenzothiophene-S,S-dioxide (DBTSO), we have introduced nonconjugated diphenylsulfone (DPSO) as the electron-deficient unit into the main chain of poly(spirobifluorene)s (PSFs). Because of the weaker electron affinity of DPSO relative to DBTSO, the charge transfer from the pendant 2,3,6,7-tetraoctyloxyfluorene to the main chain can be effectively prevented. Consequently, the resultant polymers containing DPSO moiety show pure blue emissions, which is different from DBTSO-based PSFs that exhibit undesired green emissions. With a single-layer device configuration, a peak luminous efficiency of 2.90 cd/A and a maximum luminescence of 14130 cd/m2 have been realized for the polymer PSFDPSO03. The corresponding CIE coordinates are (0.17, 0.18), nearly independent of the applied current density from 2 to 592 mA/cm2. These results indicate that tuning the electron affinity of the incorporated electron-deficient units is a very promising strategy to control the charge transfer strength for the development of blue-emitting PSFs with high efficiency and stability.

A novel polymer is developed and used as underlying interlayer to improve donor polymer/acceptor material blend morphology of active layer in polymer solar cells (PSCs). The polymer poly{N-9-[1,17-bis(diethylphosphonate)heptadecanyl]-2,7-carbazole-alt-5,5-(4,7-di-2-thienyl-2,1,3-benzothiadiazole)} (PCDTBT-Pho) is designed by attaching polar phosphonate moieties to the side chain of the donor polymer, poly[N-9-heptadecanyl-2,7-carbazole-alt-5,5-(4,7-di-2-thienyl-2,1,3-benzothiadiazole)] (PCDTBT). The pendant phosphonate moieties lead to different solubility and proper surface energy of PCDTBT-Pho. As a result, in PSC devices, the underlying PCDTBT-Pho layer facilitates the formation of biscontinuous network morphology in the active layer, makes the donor polymer enriched at the anode side, and induces the donor polymer to crystallize. These improvements contribute to improved charge separation and transport, leading to short-circuit current density enhancement by 12% and power conversion efficiency enhancement by 8% of the PSC devices. Thus, the design and application of PCDTBT-Pho indicate a novel approach to optimize active layer morphology and improve photovoltaic efficiency of PSCs.

A new A′–A–D–A–A′ type low band gap small molecule Cz-TBT-CAC8 with 2,7-carbazole as the center donor (D), benzothiadiazole as an electron acceptor (A) and alkyl cyanoacetate as another electron acceptor (A′) has been designed and synthesized as the donor material for the solution-processed bulk hetero-junction solar cells. This small molecule possesses a low lying HOMO level at −5.30 eV and an optical band gap of 1.73 eV. The solar cell based on Cz-TBT-CAC8/PC61BM blend film spin-coated from chlorobenzene solution exhibits a PCE of 2.87% with a high Voc of 1.05 V. After adding 0.2% DIO into the chlorobenzene solution as an additive, the PCE was further improved to 3.95% with a Voc of 1.03 V, a Jsc of 7.32 mA cm−2 and a FF of 0.52.

On the basis of a well-known hole transporting material, namely 4,4′,4′′-tris(carbazol-9-yl)-triphenylamine (TCTA), a series of star-shaped deep-blue fluorescent emitters (2P-TCTA, 3P-TCTA, 4P-TCTA and 5P-TCTA) have been successfully developed via a simple extension of the oligophenyl chain between two N atoms. When the number of phenyl rings increases, it is found that both the absorption and emission for these TCTA-based starbursts are red-shifted and finally become saturated for 5P-TCTA consisting of a pentaphenyl bridge. Interestingly, on going from 2P-TCTA to 5P-TCTA, the film photoluminescence quantum yield is gradually enhanced from 11.4% to 35.5%. The same trend is also observed for their corresponding solution-processed undoped OLEDs. As a consequence, 5P-TCTA shows the best device performance, revealing a maximum luminescence of 7300 cd m−2, and a peak luminous efficiency of 2.48 cd A−1 (2.15 lm W−1; 2.30%) together with CIE coordinates of (0.15, 0.09).

A series of solution processible greenish-blue-emitting Ir dendrimers with polyether dendrons that consist of N-phenylcarbazole (NPC) are developed via a convenient post-dendronization method. It involves two steps: (i) the successful preparation of a reactive Ir core, namely m-HO-dfppyIr, only when the hydroxyl group is located at the meta position relative to the N atom in the C^N ligand so as to eliminate the possible resonance structure between enol and keto; and (ii) the subsequent functionalization with NPC-based polyether dendrons to afford the first, second and third generation Ir dendrimers (Ir-G1B, Ir-G2B and Ir-G3B) with ease and high yields over 60%. All these dendritic complexes possess good thermal stability with decomposition temperatures higher than 380 °C and glass transition temperatures higher than 200 °C. In addition, with the growing generation number, the intermolecular interactions between emissive Ir cores are expected to be effectively inhibited to avoid the luminescence quenching, which is confirmed from the blue-shifted emission peak and the enhanced lifetime of Ir-G3B in the solid state. As a result, on going from Ir-G1B to Ir-G3B, the maximum luminous efficiency rises upward from 4.7 to 9.2 cd A−1 for nondoped electrophosphorescent devices. Further optimization by doping them into a dendritic H2 host leads to the improved luminous efficiencies as high as 20.0–25.2 cd A−1.

A series of solution processible deep-blue fluorescent emitters TFPC0 ∼ TFPC2 have been designed and synthesized by incorporating different generation carbazole dendrons into the 9,9-positions of the terfluorene backbone. Compared with TFPC0, the dendritic TFPC1 and TFPC2 have the elevated glass transition temperatures as well as better solubility in common organic solvents, and their high quality amorphous films can be formed via spin-coating. Noticeably, with the increasing generation number, both the intermolecular aggregate and the formation of keto defects can be effectively suppressed to avoid the appearance of the unwanted long wavelength emission. Meanwhile, the highest occupied molecular orbital (HOMO) level is gradually enhanced from TFPC0 to TFPC2, facilitating the hole injection. As a result, TFPC2 with the second generation carbazole dendrons shows the best photoluminescence and electroluminescence stability among TFPC0 ∼ TFPC2. Its corresponding solution-processed undoped device gives a state-of-art external quantum efficiency as high as 2.02% and Commission International De L'Eclairge (CIE) coordinates of (0.16, 0.04). These results indicate that the introduction of oligocarbazole is a promising strategy towards solution processible deep-blue fluorene-containing oligomers simultaneously with high spectral stability and efficiency.

Dendron engineering in self-host blue Ir dendrimers is reported to develop power-efficient nondoped electrophosphorescent devices for the first time, which can be operated at low voltage close to the theoretical limit (Eg/e: corresponding to the optical bandgap divided by the electron charge). With increasing dendron's HOMO energy levels from B-POCz to B-CzCz and B-CzTA, effective hole injection is favored to promote exciton formation, resulting in a significant reduction of driving voltage and improvement of power efficiency. Consequently, the nondoped device of B-CzTA achieves extremely low driving voltages of 2.7/3.4/4.4 V and record high power efficiencies of 30.3/24.4/16.3 lm W−1 at 1, 100 and 1000 cd m−2, respectively. We believe that this work will pave the way to the design of novel power-efficient self-host blue phosphorescent dendrimers used for energy-saving displays and solid-state lightings.

Self-host Ir dendrimers have been adopted as the nondoped emitting layer for the successful construction of multilayer green phosphorescent organic light-emitting diodes (PhOLEDs) prepared via layer-by-layer solution processing with orthogonal solvents. Unlike previous doped systems, the risk of small-molecular-phosphor redissolution by alcohols and the resultant serious batch-to-batch variation can be eliminated. Consequently, a record-high external quantum efficiency of 21.2% together with good reproducibility is achieved for the green-emitting Ir dendrimer G2, which displays sufficient alcohol resistance owing to the effective encapsulation from the second generation dendritic wedge. The obtained performance is highly competitive with those of doped devices, while avoiding the unwanted redissolution-induced batch-to-batch variation simultaneously, representing an important development in the solution fabrication of multilayer PhOLEDs based on a nondoped system.

A novel self-host red Ir dendrimer D-(PPQ)2Ir(acac) has been developed for solution-processed nondoped phosphorescent organic light-emitting diodes (PhOLEDs) by fully encapsulating the heteroleptic complex (PPQ)2Ir(acac) with oligocarbazole at both the C∧N and O∧O ligands. Due to the shielding effect of the dendritic wedge, the intermolecular interactions and luminescence quenching are found to be significantly reduced from (PPQ)2Ir(acac) to D-(PPQ)2Ir(acac). Correspondingly, the maximum external quantum efficiency (EQE) of hybrid-solution-processed electrophosphorescent devices is increased from 0.5% to 9.9%. Moreover, D-(PPQ)2Ir(acac) shows a good alcohol resistance in the presence of the large-size carbazole dendrons. Such a feature does favor the successful fabrication of all-solution-processed devices via an orthogonal solvent processing, revealing an optimized EQE as high as 11.1% (8.7 cd A−1, 6.0 lm W−1) with CIE coordinates of (0.67, 0.33). The results indicate that highly efficient solution-processed red-emitting nondoped PhOLEDs with over 10% EQE can also be realized based on a self-host phosphorescent dendrimer system.