ABi2 (IO3 )2 F5 (A=K, Rb, and Cs): A Combination of Halide and Oxide Anionic Units To Create a Large Second-Harmonic Generation Response with a Wide Bandgap.

A family of nonlinear optical materials that contain the halide, oxide, and oxyhalide polar units simultaneously in a single structure, namely ABi2 (IO3 )2 F5 (A=K (1), Rb (2), and Cs (3)), have been designed and synthesized. They crystallize in the same polar space group (P21 ) with a two-dimensional double-layered framework constructed by [BiF5 ]2- and [BiO2 F4 ]5- units connected to each other by four F atoms, in which two [IO3 ]- groups are linked to [BiO2 F4 ]5- unit on the same side. A hanging Bi-F bond of [BiF5 ]2- unit is located on the other side via ionic interaction with the layer-inserted alkali metal ions to form three-dimensional structure. The well-ordered alignments of these polar units lead to a very strong second-harmonic generation response of 12 (1), 9.5 (2), and 7.5 (3) times larger than that of potassium dihydrogen phosphate under 1064 nm laser radiation. All of them exhibited a wide energy bandgap over 3.75 eV, suggesting that they will have a high laser damage threshold.

Adamantane-based wide-bandgap host material: blue electrophosphorescence with high efficiency and very high brightness.

An adamantane-based host material, namely, 4-{3-[4-(9H-carbazol-9-yl)phenyl]adamantan-1-yl}benzonitrile (CzCN-Ad), was prepared by linking an electron-donating carbazole unit and an electron-accepting benzonitrile moiety through an adamantane bridge. In this approach, two functional groups were attached to tetrahedral points of adamantane to construct an "sp(3)" topological configuration. This design strategy endows the host material with a high triplet energy of 3.03 eV due to the disruption of intramolecular charge transfer. Although CzCN-Ad has a low molecular weight, the rigid nonconjugated adamantane bridge results in a glass transition temperature of 89 °C. These features make CzCN-Ad suitable for fabricating blue phosphorescent organic light-emitting diodes (PhOLEDs). The devices based on sky-blue phosphor bis[(4,6-difluorophenyl)pyridinato-N,C(2')](picolinato)iridium(III) (FIrpic) achieved a high maximum external quantum efficiency (EQE) of 24.1%, which is among the best results for blue PhOLEDs ever reported. Furthermore, blue PhOLEDs with bis(2,4-difluorophenylpyridinato)-tetrakis(1-pyrazolyl)borate iridium(III) (FIr6) as dopant exhibited a maximum EQE of 14.2% and a maximum luminance of 34 262 cd m(-2). To the best of our knowledge, this is the highest luminance ever reported for FIr6-based PhOLEDs.

Rb2CdBr2I2: a new IR nonlinear optical material with a large laser damage threshold.

This paper describes the synthesis, crystal structure, and photophysical properties of a new compound Rb2CdBr2I2. It crystallizes in the noncentrosymmetric space group Ama2. In the crystal, all the distorted tetrahedron [CdBr2I2](2-) groups are arranged in a way such that all the Cd-I bonds are located in the same side of the Cd atoms resulting in a net polarization. Rb2CdBr2I2 showed a powder second harmonic generation (SHG) response 4 times that of KH2PO4 (KDP). The preliminary measurement indicated that it exhibits a large laser-induced damage threshold (LDT) of 190 MW/cm(2) which is 6 times that of AgGaS2. It also exhibits a wide transparent region (0.37-14 µm) with a relatively high (up to 490 °C) thermal stability. All these indicate that Rb2CdBr2I2 is a new promising candidate for NLO materials in the IR region.

A new approach to prepare efficient blue AIE emitters for undoped OLEDs.

Two aggregation-induced emission active luminogens (TPE-pTPA and TPE-mTPA) were successfully synthesized. For comparison, another six similar compounds were prepared. Because of the introduced hole-dominated triphenylamine (TPA), fluorene groups with high luminous efficiency, and unconjugated linkages, the π conjugation length of the obtained luminogens is effectively restricted to ensure their blue emission. The undoped organic light-emitting diodes based on TPE-pTPA and TPE-mTPA exhibited blue or deep-blue emissions, low turn-on voltages (3 V), and high electroluminescence efficiencies with Lmax, ηC,max, and ηP,max values of up to 26,697 cd m(-2), 3.37 cd A(-1), and 2.40 Lm W(-1).

White polymer light-emitting diodes based on star-shaped polymers with an orange dendritic phosphorescent core.

A series of new star-shaped polymers with a triphenylamine-based iridium(III) dendritic complex as the orange-emitting core and poly(9,9-dihexylfluorene) (PFH) chains as the blue-emitting arms is developed towards white polymer light-emitting diodes (WPLEDs). By fine-tuning the content of the orange phosphor, partial energy transfer and charge trapping from the blue backbone to the orange core is realized to achieve white light emission. Single-layer WPLEDs with the configuration of ITO (indium-tin oxide)/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)/polymer/CsF/Al exhibit a maximum current efficiency of 1.69 cd A(-1) and CIE coordinates of (0.35, 0.33), which is very close to the pure white-light point of (0.33, 0.33). To the best of our knowledge, this is the first report on star-shaped white-emitting single polymers that simultaneously consist of fluorescent and phosphorescent species.

Using an organic molecule with low triplet energy as a host in a highly efficient blue electrophosphorescent device.

To achieve high efficiencies in blue phosphorescent organic light-emitting diodes (PhOLEDs), the triplet energies (T1) of host materials are generally supposed to be higher than the blue phosphors. A small organic molecule with low singlet energy (S1) of 2.80 eV and triplet energy of 2.71 eV can be used as the host material for the blue phosphor, [bis(4,6-difluorophenylpyridinato-N,C(2'))iridium(III)] tetrakis(1-pyrazolyl)borate (FIr6; T1=2.73 eV). In both the photo- and electro-excited processes, the energy transfer from the host material to FIr6 was found to be efficient. In a three organic-layer device, the maximum current efficiency of 37 cd A(-1) and power efficiency of 40 Lm W(-1) were achieved for the FIr6-based blue PhOLEDs.

Using two simple methods of Ar-Ar(F) self-assembly and isolation chromophores to further improve the comprehensive performance of NLO dendrimers.

Herein, through a combination of divergent and convergent approaches, coupled with the utilization of the powerful Sharpless "click chemistry" reaction, two series of high-generation nonlinear optical (NLO) dendrimers have been conveniently prepared in high purity and satisfactory yields. Perfluoroaromatic rings and isolation chromophores were introduced to further improve their comprehensive performance. Thanks to the effects of Ar-Ar(F) self-assembly and the isolation chromophores, coupled with perfect 3D spatial isolation from the highly branched structure of the dendrimer, G5-PFPh-NS displayed very large NLO efficiency (up to 257 pm V(-1)), which is, to the best of our knowledge, the new record highest value reported so far for simple azo chromophore moieties. High-quality wide optical transparency and good stability were also achieved.

From nitro- to sulfonyl-based chromophores: improvement of the comprehensive performance of nonlinear optical dendrimers.

Through the combination of the divergent and convergent approaches, coupled with the utilization of the powerful Sharpless "click-chemistry" reaction, two series of sulfonyl-based high-generation NLO dendrimers were conveniently prepared with high purity and in satisfactory yields. Thanks to the perfect three-dimensional (3D) spatial isolation from the highly branched structure and the isolation effect of the exterior benzene moieties and the interior triazole rings, these dendrimers exhibited large second harmonic generation coefficient (d33) values up to 181 pm V(-1), which, to the best of our knowledge, is the highest value so far for polymers containing sulfonyl-based chromophore moieties. Meanwhile, compared with the nitro-chromophore-based analogues, their optical transparency and NLO stability were improved in a large degree, due to the lower dipole moment (µ) and the special main-chain structure of sulfonyl-based chromophore in these dendrimers.

Spiroconjugated intramolecular charge-transfer emission in non-typical spiroconjugated molecules: the effect of molecular structure upon the excited-state configuration.

A set of terfluorenes and terfluorene-like molecules with different pendant substitutions or side groups were designed and synthesized, their photophysical properties and the excited-state geometries were studied. Dual fluorescence emissions were observed in compounds with rigid pendant groups bearing electron-donating N atoms. According to our earlier studies, in this set of terfluorenes, the blue emission is from the local π-π* transition, while the long-wavelength emission is attributed to a spiroconjugation-like through-space charge-transfer process. Herein, we probe further into how the molecular structures (referring to the side groups, the type of linkage between central fluorene and the 2,2'-azanediyldiethanol units, and-most importantly-the amount of pendant groups), as well as the excited-state geometries, affect the charge-transfer process of these terfluorenes or terfluorene-like compounds. 9-(9,9,9'',9''-tetrahexyl-9H,9'H,9''H-[2,2':7',2''-terfluoren]-9'-yl)-1,2,3,5,6,7-hexahydropyrido[3,2,1-ij]quinolone (TFPJH), with only one julolidine pendant group, was particularly synthesized, which exhibits complete "perpendicular" conformation between julolidine and the central fluorene unit in the excited state, thus typical spiroconjugation could be achieved. Notably, its photophysical behaviors resemble those of TFPJ with two pendant julolidines. This study proves that spiroconjugation does happen in these terfluorene derivatives, although their structures are not in line with the typical orthogonal π fragments. The spiroconjugation charge-transfer emission closely relates to the electron-donating N atoms on the pendant groups, and to the rigid connection between the central fluorene and the N atoms, whereas the amount of pendant groups and the nature of the side chromophores have little effect. These findings may shed light on the understanding of the through-space charge-transfer properties and the emission color tuning of fluorene derivatives.

Synthesis and photophysical properties of polyfluorene with dipicolylamine groups on the side chain: highly selective and sensitive detection of histidine.

Two new polyfluorenes with dipicolylamine (DPA) pendant, PF-TDPA and PF-HDPA, are designed and synthesized by pre- and post-functionalization, respectively. PF-TDPA with a rigid side chain shows a selective fluorescence quenching upon the addition of Cu(2+) in a mixture solution of tetrahydrofuran and 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES) buffer. What is more, the PF-TDPA/Cu(2+) complex can selectively detect histidine over other amino acids with a fluorescence recovery. In contrast, PF-HDPA with a flexible spacer exhibits a fluorescence quenching to Cu(2+) but slightly fluorescence recovery after the addition of histidine. This indicates that the proper distance between the two DPA groups play an important role in the detection of histidine.

New water-soluble cationic poly(p-phenylenevinylene) derivative: the interaction with DNA and selective fluorescence enhancement induced by ssDNA.

A new cationic cyano-substituted poly(p-phenylenevinylene) (N-CNPPV) is synthesized by Knoevenagel condensation. The water-soluble polymer shows different emission spectra in different solvents and displays unique fluorescent behaviors in the mixed solvents of water and THF. The new polymer can form a complex with ssDNA by adopting a more planar conformation, exhibiting red shift of emission wavelength and enhancement of fluorescence intensity. By investigating the fluorescent response of N-CNPPV to various surfactants, we demonstrate that the hydrophobic interaction and electrostatic interaction result in the selective response of N-CNPPV to ssDNA. This is the first report on selective fluorescence enhancement of conjugated polyelectrolyte induced by ssDNA.

The utilization of isolation chromophore in an "A3 +B2 " type second-order nonlinear optical hyperbranched polymer.

In this paper, a new nonlinear optical (NLO) hyperbranched polymer P1 is designed and synthesized successfully through one-pot "A3 +B2 " approach via a simple Sonogashira coupling reaction, in which isolation chromophore is introduced to improve its comprehensive performance such as NLO activity, optical transparency, and stability. For comparison, its analogs, P2 and P3, just containing one type of chromophore, are also prepared. Although P1 cannot be well poled under our test conditions, its NLO coefficient is still much higher than its analogs P2, P3, and the linear polyaryleneethynylene P4, which also contains isolation chromophore, indicating the advantages of isolation chromophore and the three-dimensional (3D) spatial isolation from the highly branched structure in the NLO field.

A new disubstituted polyacetylene bearing 6-benzylaminopurine moieties: postfunctional synthetic strategy and sensitive chemosensor towards copper and cobalt ions.

A new 6-benzylaminopurine-functionalized disubstituted polyacetylene (P2) with strong green fluorescence is successfully synthesized by utilizing the postfunctional method. The polymer is soluble in common organic solvents, and its strong green fluorescence can be quenched by copper and cobalt ions with a detection limit down to 1.0 × 10(-8) (0.64 ppb) and 3.3 × 10(-8) mol L(-1) (1.94 ppb), respectively. Moreover, not much interference is observed from other metal ions, including Li(+) , Na(+) , K(+) , Fe(3+) , Fe(2+) , Ni(2+) , Hg(2+) , Mg(2+) , Al(3+) , Zn(2+) , Mn(2+) , Pb(2+) , Ba(2+) , Ca(2+) , Cd(2+) , Ag(+) , and Cr(3+) . Furthermore, P2 can be put into application using test strips, making P2 a practical, sensitive, and selective copper and cobalt probe.

A new low-bandgap polymer containing benzene-fused quinoxaline: significantly enhanced performance caused by one additional benzene ring.

Two new alkoxy-substituted quinoxaline (Qx)-based copolymers, PBDTQx and PBDTPz, are designed and synthesized. The only difference between these two polymers is that two methyl groups of the Qx are replaced by one additional fused benzene ring. The UV-Vis absorptions, thermal stability, energy levels, field-effect carrier mobility, and photovoltaic characteristics of the two copolymers are systematically evaluated to understand the relationships between the polymer structure at the molecular level and the photovoltaic performances. Photovoltaic cells based on the PBDTPz with a structure of ITO/PEDOT:PSS/Polymer:PC(71) BM/PEO/Ca/Al exhibit a promising efficiency of 4.40%, while that of PBDTQx is relatively much poorer.

Efficient phosphorescent polymer light-emitting diodes by suppressing triplet energy back transfer.

Phosphorescent polymer light-emitting diodes (PhPLEDs) are promising devices in flat panel displays and solid state lighting sources since they can combine the advantages of the high efficiency of electrophosphorescence and low-cost, large-scale manufacture by using a solution process. However, their efficiencies are generally much lower than those of small-molecule-based devices fabricated by using a thermal deposition approach. One of the major reasons for their low efficiency is that energy is lost by back transfer to a polymer host. This tutorial review gives a brief introduction to the fundamentals of PhPLEDs, and then highlights recent progress in the main approaches to suppress triplet energy back transfer from the phosphor to the polymer host towards realizing highly efficient PhPLEDs. The suppressing mechanisms are discussed, and the achievement of high device efficiencies are demonstrated. Emphasis is placed on the relationships between molecular structure, the extent of suppressing triplet energy back transfer, and device performance.

A new mixed halide, Cs2HgI2Cl2: molecular engineering for a new nonlinear optical material in the infrared region.

A new mixed halide, Cs(2)HgI(2)Cl(2), which contains the highly polar tetrahedron of anion (HgI(2)Cl(2))(2-), has been designed and synthesized by reaction in solution. In its single crystal, the isolated (HgCl(2)I(2))(2-) groups are arranged to form chains. The chains are then further connected into a three-dimensional framework through the Cs atoms that occupy the empty spaces surrounded by halide atoms. All the polar (HgCl(2)I(2))(2-) groups align in such a way that gives a net polarization, leading it to show a phase matchable second harmonic generation (SHG) effect as strong as that of KH(2)PO(4) (KDP) based on the powder SHG measurement. It also displays excellent transparency in the range of 0.4-41 µm with relatively high thermal stability. A preliminary measurement indicates that its laser-induced damage threshold is about 83 MW/cm(2), about twice that of AgGaS(2). This study demonstrates that Cs(2)HgI(2)Cl(2) is a promising nonlinear optical material in the infrared region.

New hyperbranched polytriazoles containing isolation chromophore moieties derived from AB4 monomers through click chemistry under copper(I) catalysis: improved optical transparency and enhanced NLO effects.

By modifying a synthetic procedure, two new hyperbranched polytriazoles (HP1 and HP2) containing isolation chromophores were synthesized successfully through click chemistry reactions under copper(I) catalysis. For the first time, these two polymers were derived from an AB(4)-type monomer, although they contain different end-capping chromophores. They are soluble in normal polar organic solvents and are well characterized. Thanks to the presence of the isolation chromophore, the two polymers demonstrate good nonlinear optical (NLO) properties and optical transparency, making them promising candidates for practical applications.

Fluorescent and colorimetric probes for mercury(II): tunable structures of electron donor and π-conjugated bridge.

A new series of intramolecular-charge-transfer (ICT) molecules (compounds 1, 2, and 3) were synthesized by attaching various electron-donating thiophenes groups to a triphenylamine backbone with an aldehyde group as the electron acceptor. Based on the protection reaction between ethanethiol and aldehyde, the corresponding dithioacetals (compounds S1, S2, and S3) were prepared to serve as novel colorimetric and fluorescent chemosensors for Hg(2+) ions. Also, compound S1 was further utilized to construct the chemical-reaction-based conjugated polymer probe (PS1) towards Hg(2+) ions. In the presence of as little as 10 nM Hg(2+), compound PS1 displayed an apparent change in the fluorescent intensity. The sensing processes were revealed to be mediated by ICT, as confirmed by time-dependent DFT calculations. Furthermore, compound S1 was successfully applied to microscopic imaging for the detection of Hg(2+) in HeLa cells with ratiometric fluorescent methods.

High-generation second-order nonlinear optical (NLO) Dendrimers that contain isolation chromophores: convenient synthesis by using click chemistry and their increased NLO effects.

Herein, high-generation dendrimers G4-NS and G5-NS, which contained 30 and 62 azo-benzene chromophore moieties, respectively, were conveniently prepared in high purity and satisfied yields by a combination of divergent and convergent approaches, coupled with the utilization of the powerful Sharpless click reaction. These dendrimers possessed a regular structure of alternating layers of nitro-based and sulfonyl-based azo chromophores in which the sulfonyl-based azo-chromophore moieties were utilized as co-isolation groups for the nitro-based moieties to achieve larger macroscopic second-order nonlinear optical (NLO) effects. These high-generation dendrimers (G4-NS and G5-NS) displayed very large NLO efficiencies (up to 253.0 pm V(-1)), which is, to the best of our knowledge, the record highest efficiency for simple azo-chromophore moieties.

Solution-processed, undoped, deep-blue organic light-emitting diodes based on starburst oligofluorenes with a planar triphenylamine core.

A series of starburst oligomers (T1-T3) that contained a fully diarylmethene-bridged triphenylamine core and oligofluorene arms were designed and synthesized through Suzuki cross-coupling reactions. Their thermal, photophysical, and electrochemical properties were also investigated. These materials showed high glass transition, in the range of 123-129 °C, and good film-forming abilities. They displayed deep-blue emission both in solution and as thin films. Solution-processed devices based on these oligomers exhibited highly efficient deep-blue electroluminescence and the device performances were significantly enhanced with the extension of the oligofluorene arms. The double-layered device that contained T3 as an emitter showed a maximum current efficiency of 3.83 cd A(-1) and a maximum external quantum efficiency of 4.19% with CIE coordinates of (0.16, 0.09), which are among the highest values for undoped deep-blue OLEDs that are based on solution-processable starburst oligomers.