Film-forming Properties Research Articles

Apple pectin-based active films to preserve oil: Effects of naturally branched phytoglycogen-curcumin host

Pectin has excellent film-forming properties, but its functional properties need to be enhanced. Therefore, we constructed naturally branched phytoglycogen (PG) nanoparticles to solubilize curcumin (CCM) and further enhance the properties of apple pectin-based active films. The size of the PG spherical particles ranged from 30 to 100 nm with some aggregates. The branch density of the PG was 6.02 %. These PG nanoparticles increased the solubility of CCM nearly 1742-fold and a nanosized phytoglycogen-curcumin (PG-CCM) host was formed via hydrogen bonding and hydrophobic interaction. This host promoted the formation of pectin-based films with a dense structure and increased their tensile strength to 23.51 MPa. The coefficient to water vapor permeability, oxygen permeability and carbon dioxide permeability were all decreased indicating their barrier performance were improved. Among them, the oxygen permeability coefficient decreased most, from 1.14 × 10−7 g·m−1·s−1 to 0.8 × 10−7 g·m−1·s−1. Also, the transmittance of the active film at 280 nm and 660 nm decreased to 0.65 % and 72.10 %. Antioxidant and antibacterial properties were significantly enhanced (P < 0.05). And the results showed this film was an excellent oil packaging material. The active film incorporating PG-CCM host can replace heat-sealed plastic bags/pouch made from polyethylene and polypropylene synthetic plastics, and solve the problem that plastic packaging is difficult to degrade and cannot be squeezed clean. This provides a new conceptual framework for developing pectin-based active films by incorporating of PG and CCM.

Film-Forming, Moisturizing, and Sensory Properties of a Cosmetic Formulation Containing Tara Gum and Brazilian Berry Extracts.

The development of cosmetic formulations with moisturizing and film-forming properties has been very important to help keep skin physiology and protection. In this context, this study aimed to develop a cosmetic formulation containing Tara gum and Brazilian berry extract and evaluate its physical-mechanical, film-forming, and sensory properties. A gel formulation was developed based on Tara gum added to Plinia cauliflora extract and was characterized by its spreadability profile and sensory properties. A clinical study was carried out with ten participants to evaluate the skin microrelief, stratum corneum water content, transepidermal water loss (TEWL), and skin morphological characteristics by reflectance confocal microscopy (RCM) before and after 2h of application of the formulations. The formulation with Brazilian berry significantly decreased the work of shear parameter, which can be correlated with improved spreadability in the sensory analysis. The clinical study showed that both formulations improved skin hydration and reduced the TEWL. The RCM imaging analysis showed the visible film on the skin surface, a decrease in the size of furrows, an increase in the reflectance of the interkeratinocytes, and reflectance of the stratum corneum for both formulations. These results were more pronounced for the formulation containing Brazilian berry. The Tara gum in the gel formulation promoted the formation and visualization of a polymeric net on the stratum corneum surface, demonstrated by the images obtained from RCM. However, the formulation added with the Brazilian berry extract improved the skin microrelief, honeycomb pattern of the epidermis, and skin hydration in deeper layers of the epidermis.

Construction of fluorinated hyperbranched polyaryletherketone-based UV-cured films with low dielectric and enhanced mechanical properties

The incorporation of hyperbranched structure into the polyaryletherketone (PAEK) is a crucial method for achieving a low dielectric constant (Dk), and the inclusion of crosslinked structure effectively reduces the dielectric loss (Df). This approach is of great significance in the development of high-quality communication at high frequencies. However, it is still a significant challenge for maintaining its mechanical properties and reducing Dk and Df due to the poor film-forming properties and low ductility of hyperbranched polymers. In this study, we synthesized a novel acrylate-based fluorinated hyperbranched photosensitive polyaryletherketone (hb-P6FAEK-Ace) as a prepolymer with various bifunctional aliphatic active and 4-acryloyl morpholine as the reactive solvent. Upon UV irradiation, cured films were obtained. This method significantly improved the mechanical properties of the hyperbranched UV-cured resin, with the tensile strength of CF-DCDDA of 83.2 MPa and the elongation at break of 7.61%. Additionally, the five prepared photosensitive resins exhibited excellent rheological properties (from 71.6 mPa s to 134.7 mPa s at 100 °C), rapid curing rates (within tens of seconds), and minimal volume shrinkage (<7%). Meanwhile, the Dk of CF-DCDDA was measured to be 2.87, with a Df of 0.0126 at the frequency of 20 GHz. This low dielectric expression for the crosslinked cured films could be ascribed to the confinement of electronic polarization caused by the crosslinked and hyperbranched structures. This work provides a simple, green, and promising strategy for enhancing the dielectric and mechanical properties of hb-PAEK.

Active packaging coating based on agarose grafted with benzoic acid derivatives: Preparation, characterization and application in fish preservation

Agarose based on gel strength can not meet the needs of diverse applications, and the structural modification of agarose is helpful to improve its functional properties and promote the economic benefits of the agarose industry chain. This study focuses on making agarose as an active packaging material with specific functions. Agarose was modified with p-hydroxybenzoic acid (Ph) and 3, 4-dihydroxybenzoic acid (Da) to produce agarose derivatives with grafting rates of 4% and 12% (Ph-Ag@4%, Ph-Ag@12%, Da-Ag@4%, and Da-Ag@12%). Characterization techniques confirmed the successful introduction of Ph and Da onto agarose, with grafting occurring at the C-6 position in d-galactose. Both Ph-Ag and Da-Ag exhibited significantly enhanced antioxidant and antibacterial properties. Da-Ag@12% showed remarkable improvements in DPPH and ABTS radical scavenging activities from 0% to 66.01% and 2.49%–84.73%, respectively. Ph-Ag@12% exhibited inhibition rates of 100% against Escherichia coli and Staphylococcus aureus. After modification, Ph-Ag and Da-Ag maintained good gelling and film-forming properties. Fish preservation experiments revealed both Ph-Ag and Da-Ag coatings effectively suppressed microbial growth, slowed down lipid oxidation, minimized water loss, and maintained the texture and appearance of fish meat. These coatings improved fish meat quality and extended its shelf life, with Da-Ag@12% showing the most promising results.

Preparation And Characterization of Polyvinyl Alcohol Nanofiber Loaded With Mafenide For Sustain Release

This paper delves into the intricate process of preparing and characterizing Polyvinyl alcohol (PVA) nanofibers loaded with Mafenide to achieve sustained release functionality. The synthesis involves the careful integration of Mafenide, a pharmaceutical agent known for its antimicrobial properties, into PVA nanofibers. This combination holds promise for controlled drug delivery applications. The preparation begins with the electrospinning technique, a method widely employed for creating nanofibrous structures. During this process, the Mafenide is incorporated into the PVA matrix, forming a composite material. The choice of Polyvinyl alcohol as the base material is strategic, given its biocompatibility and excellent film-forming properties. The characterization phase involves a comprehensive analysis of the resulting nanofibers. Techniques such as scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR). are employed to examine the morphology and chemical composition of the nanofibrous system. These analyses provide insights into the structural integrity and the successful incorporation of Mafenide. The study focuses on the sustained release aspect, aiming to understand how the loaded Mafenide interacts within the PVA nanofibers over time. This sustained release mechanism is crucial for pharmaceutical applications, offering prolonged therapeutic effects and minimizing the need for frequent administration. The potential benefits of this research lie in the development of an efficient drug delivery system.

Nanobiolubricant grinding: a comprehensive review

AbstractMinimum quantity lubrication (MQL), which considers the cost, sustainability, flexibility, and quality, has been actively explored by scholars. Nanoadditive phases have been widely investigated as atomizing media for MQL, aimed at enhancing the heat transfer and friction reduction performance of vegetable-oil-based biolubricants. However, the industrial application of nano-enhanced biolubricants (NEBL) in grinding wheels and workpiece interfaces as a cooling and lubricating medium still faces serious challenges, which are attributed to the knowledge gap in the current mapping between the properties and grindability of NEBL. This paper presents a comprehensive literature review of research developments in NEBL grinding, highlighting the key challenges, and clarifies the application of blind spots. Firstly, the physicochemical properties of the NEBL are elaborated from the perspective of the base fluid and nanoadditive phase. Secondly, the excellent grinding performance of the NEBL is clarified by its distinctive film formation, heat transfer, and multiple-field mobilization capacity. Nanoparticles with high thermal conductivity and excellent extreme-pressure film-forming properties significantly improved the high-temperature and extreme-friction conditions in the grinding zone. Furthermore, the sustainability of applying small amounts of NEBL to grinding is systematically evaluated, providing valuable insights for the industry. Finally, perspectives are proposed to address the engineering and scientific bottlenecks of NEBL. This review aims to contribute to the understanding of the effective mechanisms of NEBL and the development of green grinding technologies.

Synthesis and characterization of fluorinated polyurethaneimide electro-optic waveguide material with novel structure

Abstract Structurally novel fluorinated polyurethaneimide (PUI) electro-optic polymer based on chromophore molecule b, diisocyanate MDI and anhydride BPAFDA was synthesized by stepwise polymerization of oligomer PUI with fluorinated aromatic diamines BATB and BATPP. Electro-optic (EO) PUI chain structure had the structure of polyimide and polyurethane chain segments, integrating the advantages of polyimide and polyurethane. The PUI possessed good film-forming property, a high glass transition temperature (T g = 193 °C) and good thermal stability (5 % weight loss temperature T d up to 320 °C). Y-Structured inverted ridge polymer optical waveguides were designed and fabricated using the PUI as the waveguide core material. The PUI had good optical performance with an EO coefficient (γ33) of 79 pm/V and 1.1 dB/cm optical propagation loss at a wavelength of 1550 nm. The results showed that the synthesized PUI met the performance requirements for the preparation of polymer optical waveguide devices and was suitable as a polymer electro-optic waveguide material.

Extrusion modification of prolamins from distiller's grains to facilitate the construction of biopolymer films.

Distiller's grains (DGs), which are rich in natural ingredients such as prolamins, are often used as low-value feed or discarded directly, resulting in great environmental pollution and resource waste. Prolamins from DGs (PDGs) were found to be a potential material for the construction of biopolymer films due to their good film-forming properties. In this study, extrusion processing was conducted to modify the physicochemical and structural properties of PDGs to facilitate the construction of biopolymer films with superior characteristics. Results indicated that extrusion led to improved solubility (17.91% to 39.95%) and increased disulfide bonds (1.46 to 6.13 μmol g-1) in PDGs. The total and sulfur amino acid contents of extruded PDGs were increased by 13.26% and 38.83%, respectively. New aggregation patterns were formed after extrusion according to the results of scanning electron microscopy, Fourier transform infrared spectroscopy and X-ray diffraction. Extrusion resulted in reduced surface hydrophobicity of PDGs (10 972 to 3632), sufficient evidence for which could be also found from structure analyses of PDGs. Finally, PDGs extruded at 110 °C were found to facilitate the forming of biopolymer films with superior mechanical properties, water resistance and thermal stability. Physicochemical and structural properties of PDGs were effectively modified by extrusion processing, and extrusion modification of PDGs could be a great way to facilitate the construction of biopolymer films with superior characteristics. It could provide more possibilities to extend the applications of DGs to alleviate the problems of environmental pollution and resource waste. © 2024 Society of Chemical Industry.

High thermally conductive polyimide film designed with heterostructural Cring-C3N4 filler and multilayer strategy

With the emerging of advanced flexible electronic, the PI film with excellent thermally conductive, flexible, lightweight, electrically insulating qualities is in high demand as a potential substrate and encapsulation material. Conventional thermally conductive fillers such as ceramic, metal and carbon material with high hardness, high density or electrical conductivity are unsuitable to prepare the advanced PI film. Furthermore, the confined loading of thermally conductive filler in PI matrix limited by its film-forming property is another obstacle to optimizing the thermal conductivity of PI film. In this work, the development of novel filler (carbon nitride in-plane grafted by two-dimensional carbon material, Cring-C3N4) with intrinsic thermal conductivity and a design of three-layer structure for the introduction of high filler loading have dramatically improved the thermal conductivity of PI film. Benefitting by the planar heterostructure construction of g-C3N4 and Cring, the existence of Cring increases the phonon transfer rate in g-C3N4, and the presence of g-C3N4 prevents the electron movement in the facet of Cring-C3N4 endowing its excellent electrical insulation property. The design of three-layer structure in which the first and third layers served as mechanical support layers with a fixed filler content (20 wt%). The second layer has the higher filler content to enhance the quantity of thermally conductive filler in PI film. Resultantly, the maximum out-of-plane thermal conductivity of the PI/Cring-C3N4 composite film is 1.35 Wm−1K−1, which is 10 times higher than the pure PI film. In addition, the PI/Cring-C3N4 composite film exhibit excellent photothermal conversion ability in which the saturation temperature of PI/Cring-C3N4 can reach 283.6 °C under 0.75 W/cm2 laser radiation being 6 times higher than that of the corresponding PI film. After the incorporation of Cring-C3N4, the PI composite film still has excellent thermal stability, low CTE, electrical insulation and mechanical properties. This work provides a novel idea for the preparation of advanced high thermal conductivity PI film.

Synthesis and gas transport properties of polynaphthoylenebenzimidazoles with keto- and sulfonic bridging groups

Polynaphthoylenebenzimidazoles (PNBI) with keto-(PNBI-CO) and sulfonic (PNBI-SO2) bridge groups were obtained by solid-state polycyclization of polyaminoimides (PANI) synthesized by polycondensation of 1,4,5,8-naphthalenetetracarboxylic acid dianhydride with 3,3`,4,4`-tetraaminobenzophenone and 3,3`,4,4`-tetraaminodiphenylsulfone in N-methylpyrrolidone, respectively. The polycondensation process and resulting chemical structure of PANI and PNBI were controlled by 1H NMR, 13C NMR and IR spectroscopy. It is shown that the temperature of solid-state polycyclization change makes it possible to obtain polymers of several of cyclization degrees. The experimental values of the gas permeability and diffusion coefficients for He, H2, N2, O2, CO2, CH4 were obtained. The gas solubility coefficients and the ideal selectivity for various gas pairs were calculated. It has been established that, in terms of the permeability-selectivity ratio, completely cyclized PNBIs occupy a more favorable position compared to incompletely cyclized ones. This result is important for polymer and a method selection to develop a selective layer of new composite membranes. The gas transport characteristics achieved for competely cyclized PNBI-SO2, as well as the film-forming properties, along with the very high thermal stability of polymers of this polymer class, are interest of further expanding the range of PNBI obtained, as well as the prospects for such new polymers using of in various gas separation processes.

Valorization of waste chilli stalks (Capsicum annuum) as a sustainable substrate for cellulose extraction: insights into its thermomechanical, film forming and biodegradation properties

Valorization of waste chilli stalks (Capsicum annuum) as a sustainable substrate for cellulose extraction: insights into its thermomechanical, film forming and biodegradation properties

Plasticizer–gelatin mixed solutions as skin protection materials with flexible-film-forming capability

To demonstrate the feasibility of plasticizer–gelatin solutions as novel skin protection materials from a physical aspect, we evaluated the rheological properties of the solutions and the mechanical properties and textures of their dried sheets and films. Three types of sugars and polyols were employed as organic plasticizers and mixed with gelatin in solutions at plasticizer/gelatin weight ratios of 0.13–1.67. The plasticizers minimally affected the viscosities and gelation temperatures of the gelatin solutions, but they remarkably softened dried gelatin sheets, except for propylene glycol. Glycerol exhibited the best plasticizing effects, but the sheets obtained using glycerol showed tacky textures. Preliminary investigations on the film-forming properties of the solutions on the human skin showed that the fructose–gelatin solution at a weight ratio of 1.0 formed a flexible thin film with a texture and mechanical properties similar to those of a commercially available polyurethane-based flexible film dressing. In terms of physical properties, we conclude that the fructose–gelatin solution has potential as a skin protection material that transforms from a solution to a film on the skin.

Electrochemiluminescent biosensor based on ECL-RET between Ru@TiO2-MXene and Pd@UiO-66-NH2 for the detection of carcinoembryonic antigens

Carcinoembryonic antigen (CEA) is often employed as a crucial tumor marker for both colon and rectal cancer. The assessment of CEA levels holds significant therapeutic importance in the diagnosis of these malignancies. In this study, an electrochemiluminescence immunosensor with a signal off was ingeniously designed with Ru@TiO2-MXene as the base material of the energy donor, and Pd@UiO-66-NH2 as the marker of the energy acceptor. This immunosensor was constructed based on the strong interaction between the two components of ECL-RET. Remarkably, TiO2-MXene exhibits favorable film-forming properties and electrical conductivity while effectively immobilizing Ru(bpy)32+. On the other hand, Pd@UiO-66-NH2 has excellent biocompatibility and light absorption, making it an ideal choice for use as a secondary antibody marker. The electrochemiluminescence immunosensor constructed exhibits an extensive detection range of 1 × 10−5 ng·ml−1 to 80 ng·ml−1 and a narrow detection limit of 2.65 fg·ml−1. The novel electrochemiluminescence immunosensor, as presented in this investigation, introduces a distinct methodology for CEA detection, carrying immense clinical significance in the field of colon and rectal cancer diagnosis.

Moisturizing and aroma-enhancing effects of low molecular weight fenugreek polysaccharides in cigarettes

Polysaccharides possess excellent moisturizing effects due to their abundance of hydrophilic groups and film-forming properties. Additionally, they can produce a refreshing aroma during the pyrolysis process. However, there is scarce research on their application in the tobacco field. Herein, we investigated the effects of low molecular weight fenugreek polysaccharide (FP) obtained through ethanol fractionation and DEAE-52 cellulose column chromatography on moisture retention and aroma enhancement in tobacco. The moisture retention test revealed that the addition of FP increased the moisture retention index (MRI) of tobacco by 11.72 %–16.69 %, indicating that the hydrophilic nature of polysaccharides facilitated the migration of free water in tobacco to bound water, resulting in reduced water activity. Moreover, the contact angle between polysaccharide and tobacco was <90°, enabling better infiltration into tobacco and slowing down tobacco shrinkage caused by water loss. Among all the components, EFP-20 and EFP-40 demonstrated superior performance. Furthermore, FP exhibited excellent thermal stability below 200 °C and can decomposed to produce aromatic substances at high temperatures. It also demonstrated the ability to adsorb ethyl heptanoate and thermally decompose to produce a substantial amount of heptanoic acid. Consequently, the incorporation of FP in tobacco demonstrated favorable effects on both moisturization and aroma enhancement.

Preparation, formation mechanism, and performance of nitrocellulose aqueous coating based on the anti-solvent method

The organic solvent-based nitrocellulose (NC) coatings exhibit a high volatile solvent content, leading to significant environmental pollution. Whereas, existing waterborne NC-based coating have demonstrated poor water resistance and complex application methods. Therefore, this study aims to develop a green and highly water-resistant waterborne NC-based coating system utilizing a simple anti-solvent method with two environmentally friendly plasticizers, namely acetyl tributyl citrate (ATBC) and triethyl citrate (TEC), as film-forming additives. The dynamic light scattering (DLS) studies revealed that the particle size of NC-based nanoparticles increased with an increase in ATBC content, while it remained relatively constant with an increase in TEC content. Moreover, the particle size results demonstrated that the storage stability of aqueous dispersions containing NC/ATBC (NA) was superior to those containing NC/TEC (NT). Additionally, the physicochemical properties of aqueous dispersions-based films (Ndis), including film formation, hygroscopicity, water resistance, transparency, thermal stability, and mechanical properties were evaluated using solvent-based films (Nsol) as control samples. The results demonstrated that the Ndis films exhibited a dense and uniform structure, with physical and chemical properties that were essentially comparable to those of Nsol films. However, the mechanical properties of Ndis films were somewhat influenced by the nanoparticle size, leading to reduced mechanical performance when the particle size of nanoparticles in the aqueous dispersion was excessively large. The equilibrium moisture content for NA and NT films were reduced to 1.119% and 1.872%, respectively, at a relative humidity of 95%, in comparison to pure NC films (3.975%). Simultaneously, water contact angle measurements indicated an increase from 77° for pure NC film to 89° for NA film and 82° for NT film. All films exhibited superior transparency characteristics. Overall, NA films display excellent water resistance and transparency as well as good mechanical properties.

Bicarbazole-Benzophenone-Based Twisted Donor-Acceptor-Donor Derivatives as Blue Emitters for Highly Efficient Fluorescent Organic Light-Emitting Diodes.

This paper delves into the development of a group of twisted donor-acceptor-donor (D-A-D) derivatives incorporating bicarbazole as electron donor and benzophenone as electron acceptor for potential use as blue emitters in OLEDs. The derivatives were synthesized in a reaction of 4,4'-difluorobenzophenone with various 9-alkyl-9'H-3,3'-bicarbazoles. The materials, namely, DB14, DB23, and DB29, were designed with different alkyl side chains to enhance their solubility and film-forming properties of layers formed using the spin-coating from solution method. The new materials demonstrate high thermal stabilities with decomposition temperatures >383 °C, glass transition temperatures in the range of 95-145 °C, high blue photoluminescence quantum yields (>52%), and short decay times, which range in nanoseconds. Due to their characteristics, the derivatives were used as blue emitters in OLED devices. Some of the OLEDs incorporating the DB23 emitter demonstrated a high external quantum efficiency (EQEmax) of 5.3%, which is very similar to the theoretical limit of the first-generation devices.

Food applications of bioactive biomaterials based on gelatin and chitosan.

Food packaging must guarantee the products' quality during the different operations including packing and maintenance throughout transportation and storage until to consumption. Thus, it should satisfy, both, food freshness and quality preservation and consumers health safety. Natural bio-sourced polymers have been explored as safe edible materials for several packaging applications, being interestingly carrier of bioactive substances, once added to improve films' properties. Gelatin and chitosan are among the most studied biomaterials for the preparation of edible packaging films due to their excellent characteristics including biodegradability, compatibility and film-forming property. These polymers could be used alone or in combination with other polymers to produce composite films with the desired physicochemical and mechanical properties. When incorporated with bioactive substances (natural extracts, polyphenolic compounds, essential oils), chitosan/gelatin-based films acquired various biological properties, including antioxidant and antimicrobial activities. The emerging bioactive composite films with excellent physical attributes represent excellent packaging alternative to preserve different types of foodstuffs (fruits, meat, fish, dairy products, …) and have shown great achievements. This chapter provides the main techniques used to prepare gelatin- and chitosan- based films, showing some examples of bioactive compounds incorporated into the films' matrix. Also, it illustrates the outstanding advantages given by these biomaterials for food preservation, when used as coating and wrapping agents.

Conjugated polymers of an oxa[5]helicene-derived polycyclic heteroaromatic: tailoring energy levels and compatibility for high-performance perovskite solar cells.

In the quest to enhance the efficiency and durability of n-i-p perovskite solar cells (PSCs), engineering hole-transporting conjugated polymers with well-matched energy levels, exceptional film-forming properties, rapid hole transport, and superior moduli is paramount. Here, we present a novel approach involving the customization of a conjugated polymer, designated as p-DTPF4-EBEH, comprising alternating units of an oxa[5]helicene-based polycyclic heteroaromatic (DTPF4) and 5,5'-(2,5-di(hexyloxy)-1,4-phenylene)bis(3,4-ethylenedioxythiophene) (EBEH), synthesized through palladium-catalyzed direct arylation. Relative to homopolymers p-DTPF4 and p-EBEH, p-DTPF4-EBEH demonstrates a proper HOMO energy level, hole density, and hole mobility, alongside superior film-forming capabilities. Remarkably, compared to the commonly used hole transport material spiro-OMeTAD, p-DTPF4-EBEH not only exhibits superior film-forming property and hole mobility but also offers increased modulus and improved waterproofing. Incorporating p-DTPF4-EBEH as the hole transport material in PSCs results in an average power conversion efficiency of 25.8%, surpassing the 24.3% achieved with spiro-OMeTAD. Importantly, devices utilizing p-DTPF4-EBEH demonstrate enhanced thermal storage stability at 85 °C, along with operational robustness.

Influence of cellulose nanocrystal surface chemistry and dispersion quality on latex nanocomposite stability, film formation and adhesive properties

The different surface functional groups on carboxylated and sulfated cellulose nanocrystals (CNCs) affect the latex CNC–polymer interactions.

New fluorene-based bipolar charge transporting materials.

Air-stable and solution-processable fluorene-based bipolar charge transporting materials (CTMs) were designed, synthesized, and analyzed. These CTMs feature anthraquinone, 9-fluorenone, and 9-dicyanofluorenylidine groups and exhibit good film formation properties for solvent processing. Quantum chemistry simulations and optical absorption measurements proved that several stable conformers and charge transfer complexes form inside the molecules. Hole mobilities in CTMs were around 10-4 to 10-5 cm2 V-1 s-1, while electron mobility in compounds with anthraquinone and 9-dicyanofluorenylidine groups was approximately one order of magnitude lower.