Synthesis and light emitting properties of sulfide-containing polyfluorenes and their nanocomposites with CdSe nanocrystals: A simple process to suppress keto-defect

A new series of sulfide-containing polyfluorene homopolymers and copolymers (PFS, PF1, PF3 and PF4) comprising 9,9-di[11-(decylsulfanyl)undecyl] fluorene, 9,9-dihexylfluorene, triphenylamine or benzothiadiazole moieties were synthesized by Ni(0)-mediated Yamamoto-coupling and palladium-catalyzed Suzuki polymerizations. Three other polyfluorenes (PF2, PF5 and PFC6) without sulfur atom in the alkyl side chains were also synthesized by a similar method for comparison purpose. These fluorene-based polymers were characterized using FT-IR spectroscopy, elemental analysis, DSC, TGA, photoluminescence (PL) and electroluminescence (EL) spectroscopies. The synthesized polymers PFS and PF1–PF3 emit blue light at around 440–468 nm, while copolymers PF4 and PF5 emit green light at around 540 nm. In annealing experiments, these polymer films show better stability against thermal oxidation than polymer PFC6. Sulfide-containing polymers show not only good electroluminescent color stability, but their EL spectra also remain unchanged at high driving voltage. A multi-layer electroluminescent device with the configuration of ITO/PEDOT/PF1/CsF/Al exhibited a stable sky-blue emission with color coordinates (0.21, 0.23) at 10 V, which showed a maximum brightness of 2991 cd/m² at 8 V (75 mA/cm²) and a maximum efficiency of 1.36 cd/A. Finally, by ligand exchange process, the sulfur element could form coordination bonding with quantum dots, and PLED devices using these new QDs-containing organic/inorganic hybrid materials as light-emitting layers exhibit superior or comparable EL performance compared to those without quantum dots.     

Syntheses,structures and properties of chiral Ln(III) coordination polymers based on (R)-4-(4-(1-carboxyethoxy)phenoxy)-3-fluorobenzoic acid

Two isomorphic chiral lanthanide coordination polymers (CCPs), namely, [Ln₂(cpfa)₃]_n {Ln = Yb Xu et al. (2011) and Lu Zheng et al. (2015) } {H₂cpfa = (R)-4-(4-(1-carboxyethoxy)phenoxy)-3-fluorobenzoic acid, have been synthesized under hydro(solvo)thermal conditions. Their structures have been determined by single-crystal X-ray diffraction analyses and further characterized by infrared spectra (IR), powder X-ray diffraction (PXRD), elemental analyses, thermogravimetric (TG) analyses and circular dichroism spectra (CD). Structure analysis reveals that CCPs 1 and 2 are isomorphic, crystallizing in Orthorhombic space group P2₁2₁2₁ and giving 3D rhombic framework. Further, CCP 1 show the strong NIR luminescence of Yb(III) ions, suggesting that [cpfa]^2 − is able to sensitize the luminescence of lanthanide ions efficiently. The two polymers also exhibit modest SHG efficiency indicating their potential application as optical materials. Thermogravimetric analyses show the remarkable thermal stabilities of the two lanthanide 3D frameworks up to 420 °C.     

Examining the thermo-mechanical properties of novel cyanate ester blends through empirical measurement and simulation

Three cyanate ester monomer or oligomer species: 2,2-bis(4-cyanatophenyl)propane 1, 1-1-bis(4-dicyanatophenyl)ethane 2, and the oligomeric phenolic cyanate (Primaset™ PT30) 3, are blended in various ratios to form binary mixtures, formulated with copper(II) acetylacetonate (200 ppm) in dodecylphenol (1% w/v active copper suspension) and cured (2 K/min to 150 °C + 1 h; 2 K/min to 200 °C + 3 h) followed by a post cure (2 K/min to 260 °C + 1 h). Thermal analysis using DSC reveals good agreement with literature data for the homopolymers: typical polymerisation enthalpies of ca. 97–98 kJ/mol. cyanate are obtained for 1 and 2, with slightly lower values (ca. 80–90 kJ/mol.) obtained for Primaset™ PT30. DMTA data show the possibility of using binary blends of the polymers to yield novel materials with similar thermal and mechanical properties to Primaset™ PT30, while improving the processability of the more highly aromatic oligomer. Two of the homopolymers (1 and 2) and a binary (1:1) blend of the same were simulated. Molecular dynamics experiments reveal good agreement with empirical data generated using DSC, DMTA and TGA.     

Synthesis,characterization, and photophysics of electroluminescent fluorene/dibenzothiophene- and fluorene/dibenzothiophene-S,S-dioxide-based main-chain copolymers bearing benzimidazole-based iridium complexes as backbones or dopants

A series of electroluminescent copolymers containing fluorene-2,8-disubstituted dibenzothiophene (PFD), fluorene-2,8-disubstituted dibenzothiophene-S,S-dioxide (PFDo) and phosphorescent benzimidazole-based iridium (Ir) complexes in the backbones were synthesized by the Suzuki coupling reaction. The thermal stabilities, HOMO/LUMO levels and triplet energy gap (E_T) values were enhanced with increasing contents of dibenzothiophene (D) or dibenzothiophene-S,S-dioxide (Do) segments in the copolymers. The relative intensities of phosphorescence and fluorescence were affected by the energy transfer and back transfer efficiencies between the polymer backbones and iridium units as evidenced by solid state PL and EL spectra. PLED devices with a configuration of ITO/PEDOT:PSS (50 nm)/metal-free copolymers (P1–P5), Ir-copolymers (P7–P13) and Ir-doped copolymers (P3 doped with Ir-complexes 6 and 8) (60–80 nm)/TPBI (40 nm)/LiF (1 nm)/Al (120 nm) were fabricated, and the electroluminescence (EL) efficiencies depended on the chemical constituents and triplet energies of the copolymers. The space-charge-limited current (SCLC) flow technique was used to measure the charge carrier mobilities of these copolymers, where both hole and electron mobilities were in the following order: the metal-free copolymers (P2, P3 and P5) > Ir-doped copolymers (P3 + 3 or 10 mol% Ir-complex 6) > Ir-copolymers (P7, P8, P12 and P13).     

A series of lanthanide (III) coordination polymers derived via in situ hydrothermal decarboxylation of quinoline-2,3-dicarboxylic acid

A series of one-dimensional coordination polymers assembled from LnNO₃ · 6H₂O (Ln = Sm(1), Eu(2), Tb(3), La(4), Ce(5), Pr(6), Nd(7), Dy(8)), quinoline-2,3-dicarboxylic acid (2,3-H₂qldc) and 1,10-phenanthroline (phen) formulated as [Ln(2,3-qldc)(3-qlc)(phen)]_n (3-Hqlc = quinoline-3-carboxylic acid) were obtained under hydrothermal conditions. It is remarkable that in situ hydrothermal decarboxylation was observed during preparing these polymers. Complexes 1–8 were characterized by elemental analyses, IR spectroscopy and single crystal X-ray diffraction analyses. The thermal stabilities and photoluminescence properties of these complexes have been investigated.     

Properties of phthalonitrile monomer blends and thermosetting phthalonitrile copolymers

Binary blends of biphenyl phthalonitrile and the n = 4 oligomeric phthalonitrile were prepared and characterized by differential scanning calorimetry and rheology studies. The blended phthalonitriles also were polymerized from the melt in the presence of bis[4-(4-aminophenoxy)phenyl]sulfone and the dynamic mechanical and thermal properties of the resulting copolymers were investigated. The properties of the phthalonitrile blends and copolymers were compared with those of the neat polymers. The phthalonitrile blends were found to have larger processing windows relative to that observed for the biphenyl phthalonitrile. The size of the processing window depended on the n = 4 phthalonitrile content in the blend. Dynamic mechanical measurements and thermogravimetric analysis showed that temperatures up to 425 °C were necessary to completely cure the phthalonitrile copolymers. The dynamic mechanical measurements also revealed that the fully-cured phthalonitrile copolymers did not soften or exhibit a glass transition temperature upon heating to 450 °C. Thermogravimetric analysis showed that the phthalonitrile copolymers exhibited excellent thermal stability along with long-term thermo-oxidative stability.     

Calix[4]arene–carbazole-containing polymers: Synthesis and properties

New highly fluorescent calix[4]arene-containing phenylene-alt-ethynylene-3,6- and 2,7-carbazolylene polymers (CALIX-PPE-CBZs) have been synthesized for the first time and their photophysical properties evaluated. Both polymers were obtained in good isolated yields (70–84%), having M_w ranging from 7660–26,700 g mol⁻¹. It was found that the diethynyl substitution (3,6- or 2,7-) pattern on the carbazole monomers markedly influences the degree of polymerization. The amorphous yellow polymers are freely soluble in several nonprotic organic solvents and have excellent film forming abilities. TG/DSC analysis evidences similar thermal behaviors for both polymers despite their quite different molecular weight distributions and main-chain connectivities (T_g in the range 83–95 °C and decomposition onsets around 270 °C).The different conjugation lengths attained by the two polymers dictates much of their photophysical properties. Thus, whereas the fully conjugated CALIX-PPE-2,7-CBZ has its emission maximum at 430 nm (E_g = 2.84 eV; Φ_F = 0.62, CHCl₃), the 3,6-linked counterpart (CALIX-PPE-3,6-CBZ) fluoresces at 403 nm with a significant lower quantum yield (E_g = 3.06 eV; Φ_F = 0.31, CHCl₃). The optical properties of both polymers are predominantly governed by the intrachain electronic properties of the conjugated backbones owing to the presence of calix[4]arenes along the polymer chain which disfavor significant interchain interactions, either in fluid- or solid-state.     

Two 2-D 4-connected lanthanide coordination framework based on benzimidazole-5,6-dicarboxylate and acetate mixed ligands

Two 2-D polymers, [Ln(bidc)(Ac)·H₂O]_n (Ln = Tb(1), Dy(2) H₂bidc = benzimidazole-5,6-dicarboxylic acid, HAc = acetic acid), have been successfully synthesized under hydrothermal conditions at 150 °C and characterized by elemental analysis, infrared spectra and single-crystal X-ray diffraction. Single crystal X-ray diffraction analyses reveal that the two compounds are isomorphous and exhibit one new (4,4)-connected 2-nodal (4⁴·6²)(4⁴·6²) layer-like net, stabilized by the interchain hydrogen bonding N–H?O, O–H?O and π?π stacking interactions between two benzimidazole rings. 2-D layers are further connected by the interlayer O–H?O hydrogen-bonding interactions to form a 3-D supermoleculaer network. Moreover, the luminescent property of compound 1 and thermogravimetric analyses of the two complexes 1–2 are discussed in detail.     

Construction of isostructural Ln–Ag (Ln = Eu; Tb; Dy) nano-channel heterometallic coordination frameworks based on pyrazine-2-carboxylate and oxalate ligands

The self-assembly of pyrazine-2-carboxylate and oxalate with mixed-metal salts under hydrothermal conditions gave three isostructural 3D 4d-4f coordination polymers, LnAg(ox)(2-pzc)₂ · H₂O [Ln = Eu (1); Tb (2); Dy (3)] [ox = oxalate, 2-pzc = pyrazine-2-carboxylate]. All three structures exhibit same unusual 3D nanoporous heterometallic coordination frameworks constructed by zigzag lanthanide–oxalate chains and Ag(2-pzc)₂ units. Furthermore, the luminescent properties of complexes 1 and 2 are discussed.     

Syntheses,crystal structures and luminescence properties of lanthanide coordination polymers involving in situ C–S bond cleavage of (4-pyridylthio)acetic acid

Lanthanide coordination polymers with the formula [Ln₂(C₂O₄)₃(H₂O)₆]_n (1) (Ln = Nd, 1) and [Ln₂(C₂O₄)₃(pythioH)₂(H₂O)₂]_n (Ln = Eu 2; Dy 3; Er 4) pythio = 4-pyridinethiolate) were synthesized by treating Ln^III nitrates with (4-pyridylthio)acetic acid under hydrothermal conditions. Single-crystal X-ray diffraction studies indicate that these lanthanide coordination polymers consist of extended oxalate-bridged two-dimensional layer structure. Interestingly, in situ C–S bond cleavage occurred and (4-pyridylthio)acetic acid was transformed into 4-pyridinethiolate and oxalate. The complexes 2 and 3 display strong fluorescent emission in the solid state at room temperature.     

Synthesis and photoresponsive behavior of the high-Tg azobenzene polymers via RAFT polymerization

Well-defined photo-responsive alternating copolymers, poly(4-(N-maleimido)azobenzene-alt-styrene)s (PMSts), were successfully synthesized via reversible addition–fragmentation chain transfer (RAFT) polymerization. A divinyl monomer was used in this polymerization to prepare high molecular weight azobenzene polymers. These polymers had good solubility in most organic solvents, formed films well, and had high glass transition temperatures (T_g = 174–250 °C) and were heat resistant (T_d > 320 °C). The photo-induced trans–cis isomerization of the copolymers was examined in chloroform solution. Surface-relief-gratings (SRGs) formed on the polymer films were also investigated using illumination from a linearly polarized Kr⁺ laser beam.     

Synthesis and characterization of side-chain oxazoline–methyl methacrylate copolymers bearing azo-dye

We synthesized new polymeric structures by attaching a side-chain azo-moiety on poly(oxazoline) and poly(oxazoline-co-methyl methacrylate)s. For the polymer analogous transformation, we took advantage of the highly effective ring-opening addition of carboxyl group to the oxazoline cycle. The comonomers feed ratio allowed us to control the composition of the products while the kinetic treatment, employing an integral method, revealed a statistical copolymerization tendency of 2-isopropenyl-2-oxazoline with methyl methacrylate in acetonitrile at 70 °C. The elemental analysis and ¹H NMR spectroscopy provided almost identical composition data for both the substrates and the side-chain copolymers. The UV spectroscopy sustained the quantitative addition of 4-(4-hydroxy-3,5-dimethylphenylazo)benzoic acid to the oxazoline rings. Both the unmodified copolymers and the coloured ones exhibited good thermal stabilities, up to 371 °C and 302 °C, respectively. The glass transition temperatures ranged from 141.5 to 177.5 °C and from 153.8 to 200.9 °C for the substrates and for the modified copolymers, respectively. Preliminary investigations showed fluorescence activity for all copolymers bearing azo-moieties.     

3D pillar-layered 4d–4f heterometallic coordination polymers based on pyridine-3,5-dicaboxylate and oxalate mixed ligands

Three 4d–4f heterometallic polymers, Ln₂Ag₂(Hpydc)₂(pydc)₂(ox) · 4H₂O (Ln = Nd (1), Eu (2) and Er (3); H₂Pydc = pyridine-3,5-dicarboxylic acid, H₂ox = oxalic acid), have been successfully synthesized under hydrothermal condition and structurally characterized. Single-crystal X-ray diffraction analyses reveal that three compounds are isomorphous and exhibit 3D pillar-layered coordination frameworks constructed from two-dimensional lanthanide-carboxylate layers and [Ag(pydc)]^? pillars. Furthermore, the luminescent property of compound 2 was studied.     

Lanthanide coordination polymers constructed from 5-(4-pyridyl)-isophthalic acid: Synthesis,structure and photoluminescent properties

Nine lanthanide coordination polymers [Ln₂(pyip)₃(H₂O)₄·DMF·3H₂O]_n (Ln = Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho) based on the pyip^2 − ligand {H₂pyip = 5-(4-pyridyl)-isophthalic acid} have been synthesized under solvothermal conditions. X-ray crystallographic studies reveal that 1–9 are isostructural and crystallize in the triclinic system, space group P2₁/c, and exhibit a 3D framework. Topological analysis reveals that the 3D framework can be simplified to a uninodal 6-connected pcu alpha-Po primitive cubic type structure. Meanwhile, the luminescent properties of these nine coordination polymers in the solid state are also investigated. Especially the Eu and Tb compounds show bright red and green luminescence with luminescence lifetimes of 0.39 and 0.80 ms, respectively.     

Linked macrocyclic systems. Interaction of copper(I) with tris-ring N2S2-donor macrocycles and their single-ring analogues

The interaction of two tri-linked N₂S₂-donor macrocyclic ligands, 1 (R = H) and 2 (R = H), and their related single ring derivatives, 3 (R = H) and 4 (R = CH₂C₆H₅), with copper(I) is reported. Solid 3:1 (metal:ligand) complexes of type [Cu₃L](PF₆)₃ (L = 1 and 2, R = H) and single ring derivatives of type [CuL]PF₆ (L = 3, R = H; L = 4, R = CH₂C₆H₅) were isolated; the X-ray structure of [CuL]PF₆ (L = 3, R = H) showed that the four macrocyclic donor atoms coordinate to the copper(I) in a quasi-tetrahedral manner (Cu–N 2.089, 2.096(4); Cu–S 2.239, 2.264(2) Å, X–Cu–Y 104.5(1)–115.4(1))°.     

Construction of three isostructural 3d–4f microporous coordination frameworks based on mixed nicotinate and oxalate ligands

The self-assembly of nicotinic acid and sodium oxalate with mixed 3d–4f metal salts under hydrothermal conditions gave three isostructural 3D 3d–4f coordination polymers, [LnCu(nic)₂(ox)] · xH₂O [Ln = La, x = 1 (1); Ln = Eu, x = 2 (2); Ln = Gd, x = 2 (3)] [ox = oxalate, nic = nicotinate]. All three structures exhibit same unusual 3D microporous heterometallic coordination frameworks that are built up by rare tetranuclear Ln₂Cu₂ clusters and mixed ox and nic linkers. Furthermore, the luminescent property of complex 2 has also been investigated.     

1-D networks formed by metal⋯sulfur van der Walls contacts: Novel tetrazole–thiolato Pd(II) and Pt(II) complexes

Pd(II)– and Pt(II)–azido complexes, [M(N₃)(PMe₃)₂(C–L)] {LH = 2-(2′)-thienyl pyridine; M = Pd (1), Pt(2)}, which contain σ-bonded heterocycles (L), were treated with aryl isothiocyanate (Me₂C₆H₃–NCS) to afford the corresponding Pd(II) and Pt(II) tetrazole–thiolato complexes, trans-{M[SCN₄(2,6-Me₂C₆H₃)](PMe₃)₂(C–L)} {M = Pd (3), Pt (4)}. Complexes 3 and 4 have a 1-D helical network formed by the intermolecular M?S van der Waals contacts.     

Synthesis and photovoltaic behaviors of benzothiadiazole- and triphenylamine-based alternating copolymers

A series of donor–acceptor (D–A) alternating copolymers (P1, P2 and P3) with thiophene–benzothiadiazole–thiophene–triphenylamine main chain have been synthesized by Suzuki polycondensation. P1, P2, and P3 possess medium optical band gaps of 1.99, 1.97 and 1.93 eV, respectively. Bulk heterojunction polymer solar cells (BHJ PSCs) with these polymers as donor and PC₇₁BM as acceptor showed power conversion efficiency (PCE) in the range of 2.1–2.8%. The highest PCE of 2.8 % was achieved for P1 with short circuit current (J_sc) of 7.8 mA/cm². This study offers a useful and important insight for designing triphenylamine derivative-based polymers used for efficient PSCs.     

Synthesis and ion responsiveness of optically active polyacetylenes containing salicylidene Schiff-base moieties

Acetylenic monomers containing salicylidene Schiff-base groups (1a and 1b) as well as Schiff-base and hydroxy groups (1c) were synthesized and polymerized with [(nbd)RhCl]₂/Et₃N catalyst to afford the corresponding polymers 2a–c with high molecular weights (M_n = 2.6–7.2 × 10⁵) in high yields (75–97%). Polarimetric, circular dichroism (CD), and UV–vis spectroscopic analyses indicated that the polymers formed helical structures with a predominantly one-handed screw sense. The addition of metal ions to salicylidene Schiff-base-containing polymers 2a and 2b produced insoluble polymer/metal complexes through ionic cross-linking as a result of salicylaldimine–metal ion complexation. Polymers 2b and 2c underwent a helix–coil transition upon the addition of HSO₄⁻, whereas these polymers did not exhibit responsiveness to other anions, such as F⁻, Cl⁻, and Br⁻.     

Synthesis and photovoltaic properties of novel alternating phenylenevinylene or fluorenevinylene copolymers containing perylene bisimide

Two novel alternating phenylenevinylene copolymers P6 and P12 as well as one fluorenevinylene copolymer F connected at the 1,7 bay positions with perylene bisimide were synthesized by Heck coupling. They were characterized by GPC, FT-IR, ¹H NMR, TGA, TMA, UV–vis, cyclic voltammetry and photoluminescence (PL) emission spectra. The copolymers were soluble in common organic solvents and thermally stable up to ～300 °C. Their glass transition temperatures were 48–60 °C. The long wavelength absorption maximum was located at 510–542 nm with optical band gaps of ～2.0 eV. The PL emission maximum of P6 and P12 was red-shifted relative to F. The photovoltaic performance of P6, P12 and F was also investigated.