Exceptional blueshifted and enhanced aggregation-induced emission of conjugated asymmetric triazines and their applications in superamplified detection of explosives.

A novel conjugated asymmetric donor-acceptor (CADA) strategy for preventing the redshift in photoluminescence, as well as preserving the merits of donor-acceptor architectures, was proposed and demonstrated for two triazine derivatives, which showed highly efficient, narrow, and blueshifted ultraviolet light emission in solid films along with special aggregation-induced emission behavior. A mechanism of aggregation-induced locally excited-state emission by suppressing the twisted intramolecular charge-transfer emission for the spectacular optoelectronic phenomena of these CADA molecules was suggested on the basis of both experimental measurements and theoretical calculations. By taking advantage of this special CADA architecture, fluorescent probes based on aggregates of conjugated asymmetric triazines in THF/water for the detection of explosives show superamplified detection of picric acid with high quenching constants (>1.0 × 10(7) M(-1)) and a low detection limit of 15 ppb.

Conjugated asymmetric donor-substituted 1,3,5-triazines: new host materials for blue phosphorescent organic light-emitting diodes.

Conjugated asymmetric donor-substituted 1,3,5-triazines (ADTs) have been synthesized by nucleophilic substitution of organolithium catalyzed by [Pd(PPh(3))(4)]. Theoretical and experimental investigations show that ADTs possess high solubility and thermostability, high fluorescent quantum yield (35%), low HOMO (-6.0 eV) and LUMO (-2.8 eV), and high triplet energy (E(T), 3.0 eV) according to the different substitution pattern of triazine. The application as host materials for blue PHOLEDs yielded a maximum current efficiency of 20.9 cd A(-1), a maximum external quantum efficiency of 9.8%, and a brightness of 9671 cd m(-2) at 5.4 V, making ADTs good candidates for optoelectronic devices.

Effect of Organic Substances on Nutrients Recovery by Struvite Electrochemical Precipitation from Synthetic Anaerobically Treated Swine Wastewater.

Anaerobically treated swine wastewater contains large amounts of orthophosphate phosphorus, ammonium nitrogen and organic substances with potential nutrients recovery via struvite electrochemical precipitation post-treatment. Lab-scale batch experiments were systematically conducted in this study to investigate the effects of initial pH, current density, organic substances upon nutrients removal, and precipitates quality (characterized by X-ray diffraction, scanning electron microscopy and element analysis via acid dissolution method) during the struvite electrochemical precipitation process. The optimal conditions for the initial pH of 7.0 and current density of 4 mA/cm2 favoured nutrients removal and precipitates quality (struvite purity of up to 94.2%) in the absence of organic substances. By contrast, a more adverse effect on nutrients removal, morphology and purity of precipitates was found by humic acid than by sodium alginate and bovine albumin in the individual presence of organic substances. Low concentration combination of bovine albumin, sodium alginate, and humic acid showed antagonistic inhibition effects, whereas a high concentration combination showed the accelerating inhibition effects. Initial pH adjustment from 7 to 8 could effectively mitigate the adverse effects on struvite electrochemical precipitation under high concentration combined with organic substances (500 mg/L bovine albumin, 500 mg/L sodium alginate, and 1500 mg/L humic acid); this may help improve struvite electrochemical precipitation technology in practical application for nutrients recovery from anaerobically treated swine wastewater.

Carbazole endcapped heterofluorenes as host materials: theoretical study of their structural, electronic, and optical properties.

By mimicking the molecular structure of 4,4'-bis(N-carbazolyl)-2,2'-biphenyl (CBP), which is a widely used host material, a new series of host molecules (carbazole-endcapped heterofluorenes, CzHFs) were designed by linking the hole-transporting carbazole to the core heterofluorene molecules in either meta or para positions of the heterofluorene. The aromatic cores considered in this study are biphenyl, fluorene, silafluorenes, germafluorenes, carbazole, phosphafluorene, oxygafluorene, and sulfurafluorene. To reveal their molecular structures, optoelectronic properties and structure-property relationships of the proposed host materials, an in-depth theoretical investigation was elaborated via quantum chemical calculations. The electronic structures in the ground states, cationic and anionic states, and lowest triplet states of these designed molecules have been studied with emphasis on the highest occupied molecular orbitals (HOMOs), the lowest unoccupied molecular orbitals (LUMOs), energy gaps (E(g)), triplet energy gaps ((3)E(g)), as well as some other electronic properties including ionization potentials (IPs), electron affinities (EAs), reorganization energies (λ), triplet exciton generation fraction (χ(T)), spin density distributions (SD), and absorption spectra. These photoelectronic properties can be tuned by chemical modifications of the heteroatom and the carbazole substitution at different positions. This study provides theoretical insights into the nature of host molecules, and shows that the designed CzHFs can meet the requirements of the host materials for triplet emitters.

Theoretical studies of the structural, electronic, and optical properties of phosphafluorenes.

Phosphafluorenes have drawn increasing attention recently in the applications of organic electronic devices due to their particular optoelectronic properties. To reveal their molecular structures, optoelectronic properties, and structure-property relationships of the newly emerged functional materials, an in-depth theoretical investigation was elaborated via quantum chemical calculations. The optimized geometric and electronic structures in both ground and exited states, the mobility of the hole and electron, the absorption and emission spectra, and the singlet exciton generation fraction of these novel phosphors-containing materials have been studied by density functional theory (DFT), single excitation configuration interaction (CIS), time-dependent density functional theory (TDDFT) methods, and the polarizable continuum model (PCM). The results show that the highest occupied molecular orbitals (HOMOs), the lowest unoccupied molecular orbitals (LUMOs), triplet energies ((3)E(g)), energy gaps (E(g)), as well as some other electronic properties including ionization potentials (IPs), electron affinities (EAs), reorganization energies (lambda), the singlet exciton generation fraction, radiative lifetime, and absorption and emission spectra can be easily tuned by chemical modifications of the phosphorus atom via methyl, phenyl, oxygen, sulfur, or selenium substitution, indicating that the phosphafluorenes are interesting optoelectronic functional materials, which have great potential in the applications of OLEDs, organic solar cells, organic storage, and sensors.

Synthesis, structure, and optoelectronic properties of phosphafluorene copolymers.

Copolymers of phosphafluorenes are obtained through Suzuki copolymerization. The phosphorus-containing copolymers show unique optical, electrochemical, and optoelectronic properties. Blue and white electroluminescence can be observed, depending on the modifications of the phosphorus atoms. It is the first time that conjugated polymers containing phosphafluorene have been prepared and used in PLEDs. Phosphafluorenes are new building blocks for conjugated oligomers and polymers.

A general strategy for the facile synthesis of 2,7-dibromo-9-heterofluorenes.

[reaction: see text] A facile, highly efficient, and economical procedure for the preparation of 6,6'-diiodo-4,4'-dibromo-3,3'-dimethoxylbiphenyl has been found. From this compound, a general synthetic strategy for the preparation of 2,7-dibromo-9-heterofluorenes has been developed. Five 2,7-dibromo-9-heterofluorenes have been easily synthesized for the first time according to the procedure presented, opening the door to new classes of inorganic and organometallic conjugated polymeric materials of polyheterofluorenes.

Novel h-shaped persistent architecture based on a dispiro building block system.

[structure: see text] A novel dispiro building block, dispiro[fluorene-9,5'(7'H)-diindeno[2,1-b:1',2'-d]thiophene-7',9' '-fluorene], and its two derivatives, TBP-DSFDITF and TDOF-DSFDITF, were designed and synthesized. Because of the rigidity and orthogonality of the spiro structure, TBP-DSFDITF exhibits a well-defined H-shaped architecture, which consists of two ter(biphenyls) as the arms of the H-shape and 3,4-diphenylthiophene as the rung, connecting via completely rigid dispiro linkages with two sp(3) carbon atoms.

Theoretical investigation of the tunable behavior of p-n copolymers based on oligothiophenes and 1,4-bis(oxadiazolyl)-benzene.

Semiempirical calculations were carried out on several model oligomers to investigate the tunable behavior of p-n copolymers with the repeating units constructed by oligothiophenes as the pi-excessive type blocks and 1,4-bis(oxadiazolyl) benzene as the pi-deficient type block. The calculated evolutions of the HOMO and LUMO of the model oligomers were in good agreement with the experimental oxidation and reduction potentials of the corresponding polymers. The effect of the length of the oligothiophene on the electronic structures and optical properties was elucidated by analyzing the HOMO and LUMO spatial distribution patterns of the model oligomers. When the number of thiophene rings increases, the HOMO and LUMO are contributed mostly from the oligothiophene segments and either the introduced single positive or negative charge focuses on the oligothiophene segments. The absorption spectra of polymers were also simulated by performing calculations on the corresponding oligomers. Good matches were observed between the calculated absorption spectra and the experimental UV-vis spectra of the corresponding polymers. The study shows that the backbone modification of the p-n copolymer, that is, changing the number of thiophene unit in the p-n diblock copolymer, greatly modifies the optical properties of the polymer.

The structural, electronic, and optical properties of ladder-type polyheterofluorenes: a theoretical study.

The ladder-type polyheterofluorenes were investigated theoretically by using density functional theory (DFT) to reveal their optical and electronic properties for applications in organic optoelectronic devices. The incorporation of heteroatoms (B, Si, Ge, N, P, O, and S) into the ladder-type highly fused polyfluorene backbone can influence and modify the optoelectronic properties significantly. The functionalization on the heteroatoms allows for facile derivation and incorporation of substitutes to further tune the properties. Small geometry variations between the ground, anionic/cationic, the first excited singlet and triplet states were observed due to the very rigid ladder-type coplanar backbone. Ladder-type polycarbazole was predicted to have the highest HOMO and LUMO energy levels, polyphosphafluorene oxide have the lowest HOMO energy level, polyborafluorene have the lowest LUMO energy level and bandgap, and polysulfafluorene has the highest bandgap and triplet energy. The ladder-type carbazole and borafluorene show the highest hole and electron injection abilities respectively; while sulfafluorene has the highest electron transfer rate. Most ladder-type heterofluorenes show bipolar charge transport character suggested by the reorganization energy. All of them have significantly short effective conjugation length in comparison with linear conjugated polymers. Their absorption and emission spectra were also simulated and discussed. The diversified electronic and optical properties of the ladder-type polyheterofluorenes with the different incorporated heteroatom and the substituent on it indicate their broad potential applications in organoelectronics.

The influence of the linkage pattern on the optoelectronic properties of polysilafluorenes: a theoretical study.

Polysilafluorenes have recently received increasing attention for a wide range of optoelectronic applications due to their improved performance over polyfluorenes and polycarbazoles. To reveal their molecular structures, optoelectronic properties, and structure-property relationships, a systematic study of the influence of the linkage pattern on the optoelectronic properties of polysilafluorenes was performed via quantum chemistry calculations. The optimized geometries, electronic properties, frontier molecular orbitals, singlet and triplet energies, ionization potentials, electron affinities, reorganization energies, and absorption and circular dichroism spectra of the model compounds have been calculated and analyzed. The great impacts of the linkage pattern on the structural, electronic, and optical properties of the silafluorene-based materials have been observed, and the effect mode of the linkage pattern has been discussed. Good coordination between the theoretical and experimental results has been found. The unreported poly(1,8-silafluorene)s are expected to be very interesting optoelectronic materials with high electronic bandgap (E(g)) and triplet energy ((3)E(g)), high electron injection property, high hole and electron transport properties, strong circular dichroism signals, and modest effective conjugation length, which can be used as high-performance blue or deep-blue light emitting diodes, ambipolar host materials for blue phosphorescent emitters, and helically chiral conjugated materials.

Macrospirocyclic oligomers based on carbazole and fluorene.

Monodisperse macrospirocyclic oligomers were prepared using self-condensation of the Friedel-Crafts reaction. Through the C-9s of the central fluorene units of four surrounding oligofluorenes, four carbazole units are connected in a series to form a macrocyclic core. These rodlike oligofluorenes form a rigid three-dimensional structure, affording the resulting macrocyclics a high steric hindrance for close interchain packing.

Structural, electronic, and optical properties of 9-heterofluorenes: a quantum chemical study.

Density-functional theory studies were applied to investigate the structural, electronic, and optical properties of 9-heterofluorenes achieved by substituting the carbon at 9 position of fluorene with silicon, germanium, nitrogen, phosphor, oxygen, sulfur, selenium, or boron. These heterofluorenes and their oligomers up to pentamers are highly aromatic and electrooptically active. The alkyl and aryl substituents of the heteroatom have limited influence, but the oxidation of the atom has significant influence on their molecular structures and properties. The highest occupied molecular orbital (HOMO)-lowest occupied molecular orbital (LUMO) interaction theory was successfully applied to analyze the energy levels and the frontier wave functions of these heterofluorenes. Most heterofluorenes belong to type B of interaction with low-lying LUMO and have the second kind of wave function. Carbazole and selenafluorene have type C of interaction with high-lying HOMO and the third kind of wave function. Types C and D of heterofluorenes, such as carbazole, oxygafluorene, sulfurafluorene, and selenafluorene also have high triplet state energies. The extrapolated HOMO and LUMO for polyheterofluorenes indicate that polyselenonafluorene has the lowest LUMO; polycarbazole has the highest HOMO; polyselenafluorene has the highest bandgap (E(g)); and polyborafluorene has the lowest E(g). Heterofluorenes and their oligomers and polymers are of great experimental interests, especially those having extraordinary properties revealed in this study.

pi-Conjugated chelating polymers with charged iridium complexes in the backbones: synthesis, characterization, energy transfer, and electrochemical properties.

A series of pi-conjugated chelating polymers with charged iridium (Ir) complexes in the backbones were synthesized by a Suzuki polycondensation reaction, leading to homogeneous polymeric materials that phosphoresce red light. The fluorene and bipyridine (bpy) segments were used as polymer backbones. 5,5'-Dibromobipyridine served as a ligand to form a charged iridium complex monomer with 1-(9'9-dioctylfluorene-2-yl)isoquinoline (Fiq) as the cyclometalated ligand. Chemical and photophysical characterization confirmed that Ir complexes were incorporated into the backbones as one of the repeat units by means of the 5,5'-dibromobipyridine ligand. Chelating polymers showed almost complete energy transfer from the host fluorene segments to the guest Ir complexes in the solid state when the feed ratio was 2 mol %. In the films of the corresponding blend system, however, energy transfer was not complete even when the content of Ir complexes was as high as 16 mol %. Both intra- and intermolecular energy-transfer processes existed in this host-guest system, and the intramolecular energy transfer was a more efficient process. All chelating polymers displayed good thermal stability, redox reversibility, and film formation. These chelating polymers also showed more efficient energy transfer than the corresponding blended system and the mechanism of incorporation of the charged Ir complexes into the pi-conjugated polymer backbones efficiently avoided the intrinsic problems associated with the blend system, thus offering promise in optoelectronic applications.