Syntheses of Conjugated Polymers for Photonics

Summary: By the Suzuki coupling reaction of 9,9-dioctyl-2,7-bis(1,3,2-dioxaborinan-2-yl)fluorene ( I ) and 3,5-di-tert-butylphenyl 2,5-dibromobenzenesulfonate ( II ) the alternating poly{[9,9-dioctylfluoren-2,7-diyl]-alt-[2-(3,5-di-tert-butyl-phenoxysulfonyl)-1,4-phenylene]} ( III ) was synthesized. Alkaline hydrolysis of III gave a conjugated polyelectrolyte carrying sulfonic acid groups ( IV ). Monomers 2,5-dibromo-3-[2-(pyren-1-yl)vinyl]thiophene and 2,5-dibromo-3-[2-(quinolin-4-yl)vinyl)thiophene were prepared and copolymerized with I to afford poly{[9,9-dioctylfluoren-2,7-diyl]-alt-[3-(2-(pyren-1-yl)vinyl)thiophen-2,5-diyl]} ( V ) and poly{[9,9-dioctylfluoren-2,7-diyl]-alt-[3-(2-(quinolin-4-yl)-vinyl)thiophen-2,5-diyl] ( VI ), respectively. Conjugated backbone of V contains the conjugated pyrene unit in the side chain. Similarly the side chain of VI contains the conjugated quinoline structure unit which can be for instance protonated. By the Suzuki polycondensation reaction of I and of the prepared methyl 3-(2,7-dibromocarbazole-9-yl)propionate ( VII ) the new poly{[9,9-dioctylfluorene-2,7-diyl]-alt-[9-(2-methoxycarbonylethyl)carbazole-2,7-diyl]} ( VIII ) was synthesized and characterized.     

Novel blue‐greenish electroluminescent poly(fluorenevinylene‐alt‐dibenzothiophenevinylene)s and their model compounds

Poly(9,9‐dihexylfluorene‐2,7‐vinylene‐alt‐dibenzothiophene‐2,8‐vinylene) (PS) and poly(9,9‐dihexylfluorene‐2,7‐vinylene‐alt‐dibenzothiophene‐5,5‐dioxide‐2,8‐ vinylene) (PSO) as well as corresponding model compounds were synthesized by Heck coupling. Both the polymers and model compounds were readily soluble in common organic solvents such as tetrahydrofuran, dichloromethane, chloroform, and toluene. The polymers showed a decomposition temperature at ～430 °C and a char yield of about 65% at 800 °C in N₂. The glass‐transition temperatures of the polymers were almost identical (75–77 °C) and higher than those of the model compounds (26–45 °C). All samples absorbed around 390 nm, and their optical band gaps were 2.69–2.85 eV. They behaved as blue‐greenish light emitting materials in both solutions and thin films, with photoluminescence emission maxima at 450–483 nm and photoluminescence quantum yields of 0.52–0.72 in solution. Organic light‐emitting diodes with an indium tin oxide/poly(ethylene dioxythiophene):poly(styrene sulfonic acid)/polymer/Mg:Ag/Ag configuration with polymers PS and PSO as emitting layers showed green electroluminescence with maxima at 530 and 540 nm, respectively. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6790–6800, 2006     

Synthesis of regio- and stereoselective alkoxy-substituted spirobifluorene derivatives for blue light emitting materials

Three new octyloxy substituted spirobifluorenes, 2,7-diphenyl-3′,6′-bis(octyloxy)-9,9′-spirobifluorene (DPBSBF, 1a), 2,7-dibiphenyl-3′,6′-bis(octyloxy)-9,9′-spirobifluorene (DBBSBF, 1b) and 2,7-diterphenyl-3′,6′-bis(octyloxy)-9,9′-spirobifluorene (DTBSBF, 1c) were prepared. All the compounds had been fully characterized by ¹H and ¹³C NMR, UV-Vis, DSC, mass spectrometry and gave satisfactory elemental analyses. They possessed good solubility in common organic solvents and good homogeneous film formation. The optical energy band gap of DBBSBF was 3.27 eV between the HOMO energy level, 5.85 eV, measured by UPS and the LUMO, 2.58 eV, calculated from absorption spectrum. A blue organic light emitting diode (OLED) based on the structure of ITO/TPD (60 nm)/DBBSBF (40 nm)/Alq₃ (20 nm)/LiF (1 nm)/Al (100 nm) showed good performance. The luminance of 3125 cd/m² was observed at a drive voltage of 12.8 V and the colour coordinate in CIE chromaticity was (0.14, 0.12). The external quantum efficiency was obtained to be 2.8% at 100 cd/m².     

Synthesis,Structure, and Photophysical Properties of Yellow-Green and Blue Photoluminescent Dinuclear and Octanuclear Copper(I) Iodide Complexes with a Disilanylene-Bridged Bispyridine Ligand

The synthesis, structural, and photophysical investigations of CuI complexes with a disilanylene-bridged bispyridine ligand 1 are herein presented. Dinuclear (2) and ladder-like (3) octanuclear copper(I) complexes were straightforwardly prepared by exactly controlling the ratio of CuI/ligand 1. Single-crystal X-ray analysis confirmed that dinuclear complex 2 had no apparent π…π stacking whereas octanuclear complex 3 had π…π stacking in the crystal packing. In the solid state, the complexes display yellow-green (λ_em = 519 nm, Φ = 0.60, τ = 11 µs, 2) and blue (λ_em = 478 nm, Φ = 0.04, τ = 2.6 µs, 3) phosphorescence, respectively. The density functional theory calculations validate the differences in their optical properties. The difference in the luminescence efficiency between 2 and 3 is attributed to the presence of π…π stacking and the different luminescence processes.     

含烷基侧链聚芴基苯并二噁唑聚合物的合成及性能研究

通过溶液缩聚的方法合成了一种含烷基侧链聚芴基苯并二噁唑聚合物(PBOPFx),讨论了聚合物的光物理性能、热性能和溶解性能.结果表明,在甲基磺酸(MSA)溶液中,PBOPFx紫外吸收显示出最大吸收峰为466 nm左右的蓝光发射,与PBO相比,最大紫外吸收峰和最大荧光发射峰均发生了明显红移,这是由于芴单元的引入,提高了聚合物的共轭程度,加强了对电子的束缚能力.此外,比较了PBOPFx在320 nm处和430 nm处激发得到的荧光发射光谱,预测聚合物中存在两种共轭单元,通过测定氧化还原曲线以及讨论stokes位移,验证了这个假设,但是由于两种共轭单元并没有出现明显的分离现象,同时还伴有电子传输杂化,致使PBOPFx主要显示出共轭长度大的单元的吸收和发射.另外由于芴单元中烷基侧链的存在,聚合物(PBOPFx)的热稳定性远低于聚亚苯基苯并二噁唑聚合物(PBO),起始分解温度在350℃左右,溶解性方面,PBOPFx有了很大的改善,在大多数有机溶剂中能较好溶解.     

Solid-State Structures and Photoluminescence of Lamellar Architectures of Cu(I) and Ag(I) Paddlewheel Clusters with Hydrogen-Bonded Polar Guests

Two hexanuclear paddlewheel-like clusters appending six carboxylic-acid pendants have been isolated with the inclusion of polar solvent guests: [Cu₆(Hmna)₆]·7DMF (1·7DMF) and [Ag₆(Hmna)₆]·8DMSO (2·8DMSO), where H₂mna = 2-mercaptonicotininc acid, DMF = N,N’-dimethylformamide, and DMSO = dimethyl sulfoxide. The solvated clusters, together with their fully desolvated forms 1 and 2, have been characterized by FTIR, UV–Vis diffuse reflectance spectroscopy, TG-DTA analysis, and DFT calculations. Crystal structures of two solvated clusters 1·7DMF and 2·8DMSO have been unambiguously determined by single-crystal X-ray diffraction analysis. Six carboxylic groups appended on the clusters trap solvent guests, DMF or DMSO, through H-bonds. As a result, alternately stacked lamellar architectures comprising of a paddlewheel cluster layer and H-bonded solvent layer are formed. Upon UV illumination (λ_ex = 365 nm), the solvated hexasilver(I) cluster 2·8DMSO gives intense greenish-yellow photoluminescence in the solid state (λ_PL = 545 nm, Φ_PL = 0.17 at 298 K), whereas the solvated hexacopper(I) cluster 1·7DMF displays PL in the near-IR region (λ_PL = 765 nm, Φ_PL = 0.38 at 298 K). Upon complete desolvation, a substantial bleach in the PL intensity (Φ_PL < 0.01) is observed. The desorption–sorption response was studied by the solid-state PL spectroscopy. Non-covalent interactions in the crystal including intermolecular H-bonds, CH⋯π interactions, and π⋯π stack were found to play decisive roles in the creation of the lamellar architectures, small-molecule trap-and-release behavior, and guest-induced luminescence enhancement.     

Modification of the Nutritional Quality and Oxidative Stability of Lupin (Lupinus mutabilis Sweet) and Sacha Inchi (Plukenetia volubilis L.) Oil Blends

Andean lupin (Lupinus mutabilis) oil is rich in monounsaturated (54.2%) and polyunsaturated (28.5%) fatty acids but has a ω-3:ω-6 ratio (1:9.2) above the recommended values for human health. Sacha inchi (Plukenetia volubilis) oil presents a high polyunsaturated fatty acid content (linolenic 47.2% and linoleic 34.7%), along a ω-3:ω-6 ratio (1:0.74) good for human consumption. The objective of this research was to study the physico-chemical properties and oxidative stability of tarwi and sacha inchi oil blends (1:4, 1:3, 1:1, 3:1 and 4:1 w:w) with suitable ω-3:ω-6 ratios. All blends showed ω-3:ω-6 ratios between 1:0.8 and 1:1.9, acceptable from a nutritional point of view, and high total tocopherols’ content (1834–688 mg/kg), thanks to sacha inchi. The oxidative stability index (OSI) of the mixtures by the Rancimat method at 120 °C ranged from 0.46 to 8.80 h. The shelf-life of 1:1 tarwi/sacha inchi oil blend was 1.26 years; its entropy (−17.43 J/mol), enthalpy (107.04 kJ/mol), activation energy (110.24 kJ/mol) and Gibbs energy (113.76 kJ/mol) suggest low oxidation reaction rates and good stability. Hence, balanced blends of tarwi/sacha inchi oils can achieve optimal nutritional properties and enhanced shelf-life.     

New Charge Transfer Complexes of K+-Channel-Blocker Drug (Amifampridine; AMFP) for Sensitive Detection; Solution Investigations and DFT Studies

UV–Vis spectroscopy was used to investigate two new charge transfer (CT) complexes formed between the K⁺-channel-blocker amifampridine (AMFP) drug and the two π-acceptors 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) and tetracyanoethylene (TCNE) in different solvents. The molecular composition of the new CT complexes was estimated using the continuous variations method and found to be 1:1 for both complexes. The formed CT complexes’ electronic spectra data were further employed for calculating the formation constants (K_CT), molar extinction coefficients (ε_CT), and physical parameters at various temperatures, and the results demonstrated the high stability of both complexes. In addition, sensitive spectrophotometric methods for quantifying AMFP in its pure form were proposed and statistically validated. Furthermore, DFT calculations were used to predict the molecular structures of AMFP–DDQ and AMFP–TCNE complexes in CHCl₃. TD-DFT calculations were also used to predict the electronic spectra of both complexes. A CT-based transition band (exp. 399 and 417 nm) for the AMFP–TCNE complex was calculated at 411.5 nm (f = 0.105, HOMO-1 → LUMO). The two absorption bands at 459 nm (calc. 426.9 nm, f = 0.054) and 584 nm (calc. 628.1 nm, f = 0.111) of the AMFP–DDQ complex were theoretically assigned to HOMO-1 → LUMO and HOMO → LUMO excitations, respectively.     

Wide bandgap OPV polymers based on pyridinonedithiophene unit with efficiency >5%

We report the properties of a new series of wide band gap photovoltaic polymers based on the N-alkyl 2-pyridone dithiophene (PDT) unit. These polymers are effective bulk heterojunction solar cell materials when blended with phenyl-C₇₁-butyric acid methyl ester (PC₇₁BM). They achieve power conversion efficiencies (up to 5.33%) high for polymers having such large bandgaps, ca. 2.0 eV (optical) and 2.5 eV (electrochemical). Grazing incidence wide-angle X-ray scattering (GIWAXS) reveals strong correlations between π–π stacking distance and regularity, polymer backbone planarity, optical absorption maximum energy, and photovoltaic efficiency.     

DFT based Monte Carlo simulations of poly(9,9-dialkylfluorene-2,7-diyl) polymers in solution

The dilute solution properties of poly(9,9-dihexylfluorene-2,7-diyl) (PDHF) were studied by coupled SEC/light scattering and MALDI-TOF over a large molecular weight (MW) span ranging from PDHF oligomers (1-8-mer) to high MW polymer. The results were compared with Monte Carlo simulations based on realistic PDHF models obtained from X-ray data and density functional theory (DFT) calculations and with a DFT based Kratky-Porod-Benoit-Doty (KPBD) worm-like chain. The simulations called "selective random walk" (SRW) and the corresponding "selective self-avoiding random walk" (SSAW) explicitly take into account the rotationally labile bonds between the fluorene units in that four distinct torsion angles (+/-37.5 and +/-143 degrees) between the units are chosen randomly. The simulations better account than the KPBD model for the experimental data obtained by us and others for various poly(9,9-dialkylfluorene-2,7-diyl) polymers but still give somewhat larger values for the radii of gyration and hydrodynamic volumes. The torsion angle selectivity of the SRW and SSAW simulations predict long chain sections punctuated by sudden sharp loops.     

A two-dimension medium band gap conjugated polymer based on 5,10-bis(alkylthien-2-yl)dithieno[3,2-d:3′,2′-d′]benzo[1,2-b:4,5-b′]dithiophene: Synthesis and photovoltaic application

A two-dimension medium band gap copolymer poly{5,10-bis(4,5-didecylthien-2-yl)dithieno[2,3-d:2′,3′-d′]benzo[1,2-b:4,5-b′]dithiophene-2,7-diyl-alt-2,5-di(3-octylthien-2-yl) thiophen-5,5′-diyl}, named as PDTBDT-T-3T, was prepared by the palladium-catalyzed Stille cross coupling reaction and characterized. The resulting polymer exhibits good solubility in common organic solvents, excellent thermal stability, and extensive light absorption from 300 nm to 650 nm with an optical band gap of 1.92 eV, the highest occupied molecular orbital (HOMO) level of ?5.03 eV and the hole mobility up to 1.92 × 10^?4 cm²·V^?1·s^?1. The power conversion efficiencies (PCEs) of 2.02%–3.19% have been achieved in the traditional PVCs for the copolymer. It should be noted that the PCEs of 4.2% for the inverted PVCs from the copolymer with PFN (poly[(9,9-bis(3′-(N,N-dimethylamino)propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctyl- fluorene)]) as cathode modifying interlayer, were similar with the PCEs of 4.39% for the inverted PVCs from P3HT:PC₇₁BM at the same condition. These results indicated that the copolymer could be used as potential candidate for P3HT.     

Poly(o-methoxyaniline) Chain Degradation Based on a Heat Treatment (HT) Process: Combined Experimental and Theoretical Evaluation

Poly(o-methoxyaniline) emeraldine-salt form (ES-POMA) was chemically synthesized using hydrochloric acid and subjected to a heat treatment (HT) process for 1 h at 100 °C (TT₁₀₀) and 200 °C (TT₂₀₀). The HT process promoted a progressive decrease in crystallinity. The Le Bail method revealed a decomposition from tetrameric to trimeric-folded chains after the HT process. The unheated POMA-ES presented a globular vesicular morphology with varied micrometric sizes. The heat treatment promoted a reduction in these globular structures, increasing the non-crystalline phase. The boundary length (S) and connectivity/Euler feature (χ) parameters were calculated from the SEM images, revealing that ES-POMA presented a wide distribution of heights. The TT₁₀₀ and TT₂₀₀ presented a narrow boundary distribution, suggesting smoother surfaces with smaller height variations. The UV-VIS analysis revealed that the transition at 343 nm (nonlocal π → π*) was more intense in the TT₂₀₀ due to the electronic delocalization, which resulted from the reduced polymer chain caused by the HT process. In addition to the loss of conjugation, counter ion withdrawal reduced the ion-chain interaction, decreasing the local electron density. This result shows the influence of the chlorine counter ions on the peaks position related to the HOMO → LUMO transition, since the π → polaron transition occurs due to the creation of the energy states due to the presence of counter ions. Finally, the electrical conductivity decreased after the HT process from 1.4 × 10⁻⁴ S.cm⁻¹ to 2.4 × 10⁻⁶ S.cm⁻¹ as result of the polymer deprotonation/degradation. Thus, this paper proposed a systematic evaluation of the POMA molecular structure and crystallite size and shape after heat treatment.     

Interaction between the conjugated polyelectrolyte poly{1,4-phenylene[9,9-bis(4-phenoxybutylsulfonate)]fluorene-2,7-diyl} copolymer and the lecithin mimic 1-O-(l-Arginyl)-2,3-O-dilauroyl-sn-glycerol in aqueous solution

In this paper, the interaction between the water-soluble conjugated polyelectrolyte poly{1,4-phenylene[9,9-bis(4-phenoxybutylsulfonate)]fluorene-2,7-diyl} copolymer and the amino acid glyceride conjugate 1-O-(L-arginyl)-2,3-O-dilauroyl-sn-glycerol dichlorohydrate (a mimic for the phospholipid lecithin) has been studied in aqueous solution by electronic spectroscopy (absorption and fluorescence) and small-angle neutron scattering (SANS). A significant increase in the polymer fluorescence and blue shift in its emission are observed on association with the surfactant. This is suggested to be due to breakup of polymer aggregates. In addition, the spectroscopic and photophysical data suggest this is followed by the vesicle to ribbon transition characteristic of this surfactant, leading to incorporation of single chains of the polymer within mixed polymer-surfactant aggregates. Support for this comes from preliminary SANS measurements, from which evidence for polymer dissolution and formation of two-dimensional structures has been obtained.     

Carbon-rich organometallics: synthesis and characterization of new ferrocenyl end-capped bis(butadiynyl) fluorene derivatives

A new series of ferrocenyl end-capped bis(butadiynyl) fluorene complexes [(η⁵-C₅H₅)Fe(η⁵-C₅H₄)CCCCRCCCC(η⁵-C₅H₄)Fe(η⁵-C₅H₅)] (R = fluoren-9-one-2,7-diyl, 1; 9,9-dihexylfluorene-2,7-diyl, 2; 9-ferrocenylmethylenefluorene-2,7-diyl, 3; 9-ferrocenylphenylmethylenefluorene-2,7-diyl, 4) have been synthesized in moderate yields by the oxidative coupling reactions of ethynylferrocene with half equivalents of the appropriate diethynylfluorene derivatives. All the new complexes have been characterized by FTIR, NMR and UV-vis spectroscopies and fast atom bombardment mass spectrometry. The molecular structures of selected molecules have been determined by X-ray crystallographic techniques. The electronic absorption and redox properties of these carbon-rich molecules were investigated and the data were compared with those for the corresponding 2,7-bis(ferrocenylethynyl)fluorene counterparts. Cyclic voltammetry indicates that the half-wave potential of the terminal ferrocenyl moieties becomes more anodic when the number of ethynyl units increases and when the 9-substituent of the central fluorene ring changes from an electron-donating group to an electron-deficient group.     

Assignment of Absolute Configuration of Bromoallenes by Vacuum-Ultraviolet Circular Dichroism (VUVCD)

A new application of vacuum-ultraviolet circular dichroism (VUVCD), which enables the measurement of CD spectra in the vacuum-ultraviolet region (140–200 nm), for the assignment of the absolute configurations of bromoallenes is described. Bromoallene moieties are found in natural products obtained from many marine organisms. To date, the absolute configuration of bromoallenes has been assigned almost exclusively with Lowe’s rule, which is based on specific rotation. However, exceptions to Lowe’s rule have been reported arising from the presence of other substituents with large specific rotations. For the unambiguous assignment of the absolute configuration of the bromoallene moiety with its characteristic absorption wavelength at 180–190 nm due to the π–π* transition, VUVCD was applied to four pairs of bromoallene diastereomers prepared by modifying the synthetic scheme of omaezallene. The VUVCD spectra clearly showed positive or negative Cotton effects around 180–190 nm according to the configuration of the bromoallene employed, revealing the potential of VUVCD for determining absolute stereochemistry.     

Investigations of photochromism of 4-(2',4'-dinitrobenzyl)-pyridine by nanosecond laser absorption spectroscopy

The photochromism of 4-(2',4'-dinitrobenzyl)-pyridine was investigated by means of laser flash photolysis. Two coloured transients were observed in the spectral ranges of 390–430 nm and 510–590 nm in ethanol and acetonitrile. The first band (390–430 nm, lifetime ≈ 100–500 ns) is the absorption band of the aci-nitro form and the second band (510–590 nm, lifetime ? 0.5 s) is the absorption band of the polymethine form of 4-(2',4'-dinitrobenzyl)-pyridine. The measurements showed that the lifetime of the aci-nitro form depends on the energy of the laser flash in the case of the acetonitrile solution. Such dependence was not observed in ethanol solution. No short-lived transients were detected in n-heptane solution.     

Preservative Effect on Canned Mackerel (Scomber colias) Lipids by Addition of Octopus (Octopus vulgaris) Cooking Liquor in the Packaging Medium

The preservative properties of waste liquor obtained from octopus (Octopus vulgaris) cooking were investigated. Three different concentrations (high, medium, and low) of octopus cooking liquor (OCL) were included, respectively, in the aqueous packaging medium employed for mackerel (Scomber colias) canning. As a result, the canning process led to an increase (p < 0.05) of lipid content, lipid oxidation (development of fluorescent compounds and thiobarbituric acid reactive substances, TBARS), lipid hydrolysis (formation of free fatty acids, FFA) and ω3/ω6 ratio in fish muscle. In all canned samples, primary (peroxides) and secondary (TBARS) levels of lipid oxidation were low. Remarkably, the presence in the packaging medium of the high and medium OCL concentrations led to lower (p < 0.05) lipid oxidation development (fluorescent compound and TBARS detection, respectively). Furthermore, an increasing OCL presence led to an average decrease of peroxide and FFA content and to an average increase of the polyene index (PI). All OCL-packaged muscle showed lower average values of saturated fatty acids and ω3/ω6 ratio and higher average values of PI and monounsaturated fatty acid presence. This study provides a first approach to novel and beneficial use of the present marine waste to inhibit lipid damage of commercial canned fish.     

1,2,4-Triazoles—XXXIII: Photodimerization of some sym-di(3-s-triazolo-[4,3-a]pyridyl)-alkanes and related derivatives

Irradiation of 3,3'-[ethane-1,2-diyl]bis-[1,2,4-triazolo-[4,3-a]pyridine] at 300 nm gave the cisoid-fused cyclobutane dimer 5aα,5bα-10bα,10cα-tetrahydro-1,10-ethano-2,3,8,9,10a,10d-hexaazadicyclopenta[a,i]biphenylene. Under the same conditions 3,3'-[propane-1,3-diyl]bis-[1,2,4-triazolo[4,3-a]pyridine] gave the corresponding cyclobutane dimer, 5aα,5bα,10bα,10cα-tetrahydro-1,10-propano-2,3,8,9,10a,10d-hexaazadicyclopenta[a,i]biphenylene whereas at 254 nm the photoproduct obtained had the “cage-like” structure 3b,3c,3d,3e,6b,6c,6d,6e-octahydro-3, 4-propano-1,2,3a,3f,5,6-hexaazadicyclobuta[def,jkl]dicyclopenta[b,h]biphenylene. Replacement of the hydrocarbon linkage with the oxybis(methylene) or a thiobis(methylene) unit and irradiation at 300 nm gave the corresponding cisoid-fused, cyclobutane dimers only. The effect of methyl substituents in the pyridine ring of the bicyclic system on the dimerization process was also studied.     

Carbazole-functionalized polyfluorenes: synthesis and conformational properties in chloroform solution and β-phase formation in copolyfluorene films

Novel copolyfluorenes (CPFs) containing 2.5 or 10 mol% of carbazole-2,7-diyl (2,7-Cz) or carbazole-3,6-diyl (3,6-Cz) derivatives in the backbone have been synthesized by means of palladium-catalyzed Suzuki polymerization under microwave irradiation. The structure of the CPF polymers was also modified by insertion of additional 2-ethylhexyl or carbazole, diaryloxadiazole, or triphenylamine units via 3,6-Cz or 2,7-Cz comonomer units in the side chains of polymers. The self-organization of molecules in chloroform solutions was investigated using light scattering and within a wide concentration interval. Analysis of the behavior of the CPFs showed that the synthesized copolymers have an increased equilibrium rigidity of molecules with a Kuhn segment length A = (10–15) nm. The A value decreases with the introduction of Cz-units into the macromolecule in the meta-position. It is shown that chemical structure of the CPFs and thermal treatment in the temperature range 60–150 °C have a dominant effect on the optoelectronic properties as well as on microstructures of their films.     

Optimising the Polyphenolic Content and Antioxidant Activity of Green Rooibos (Aspalathus linearis) Using Beta-Cyclodextrin Assisted Extraction

Antioxidant activity associated with green rooibos infusions is attributed to the activity of polyphenols, particularly aspalathin and nothofagin. This study aimed to optimise β-cyclodextrin (β-CD)-assisted extraction of crude green rooibos (CGRE) via total polyphenolic content (TPC) and antioxidant activity assays. Response surface methodology (RSM) permitted optimisation of β-CD concentration (0–15 mM), temperature (40–90 °C) and time (15–60 min). Optimal extraction conditions were: 15 mM β-CD: 40 °C: 60 min with a desirability of 0.985 yielding TPC of 398.25 mg GAE·g⁻¹, metal chelation (MTC) of 93%, 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radical scavenging of 1689.7 µmol TE·g⁻¹, ferric reducing antioxidant power (FRAP) of 2097.53 µmol AAE·g⁻¹ and oxygen radical absorbance capacity (ORAC) of 11,162.82 TE·g⁻¹. Aspalathin, hyperoside and orientin were the major flavonoids, with quercetin, luteolin and chrysoeriol detected in trace quantities. Differences (p < 0.05) between aqueous and β-CD assisted CGRE was only observed for aspalathin reporting the highest content of 172.25 mg·g⁻¹ of dry matter for extracts produced at optimal extraction conditions. Positive, strong correlations between TPC and antioxidant assays were observed and exhibited regression coefficient (R²) between 0.929–0.978 at p < 0.001. These results demonstrated the capacity of β-CD in increasing polyphenol content of green rooibos.