Fluorous gallic acid derivatives as versatile gelators. Self-assembly into nanosized fibers or balls

A new class of low molecular mass organogelators, the fluorous derivatives of gallic acid 1–3, is described. The gelation properties have been examined in a large variety of organic liquids. The corresponding analogs possessing alkyl instead of semiperfluoroalkyl chains (4–6) do not display any gelation properties, thus revealing the key role of perfluorinated chains in the aggregation/gelation process. Gels have been studied by scanning electron microscopy, revealing the presence of three-dimensional networks of nanosized fibers. In the case of an instable gel, SEM images showed that these elongated fibers curl up into nanoballs, failing to create the entangled network responsible for solvent entrapment.     

Studies of thermal properties of di(methacryloyloxymethyl)naphthalene–divinylbenzene (DMN–DVB) copolymer and its alkyl-bonded derivatives

This paper presents the thermal properties of highly crosslinked di(methacryloyloxymethyl)naphthalene–divinylbenzene (DMN–DVB) copolymeric microspheres containing polar groups in the structure and their alkyl-bonded derivatives. C₈ and C₁₈ alkyl chains were introduced into the aromatic rings of the DMN–DVB porous copolymer by means of the Friedel–Crafts reaction. As a source of C₈ and C₁₈ alkyl chains, octyl and octadecyl chlorides were used. It was necessary to check whether the introduction of alkyl chains into the structure of polymeric packing had an impact on its thermal properties. The studies were carried out by thermogravimetry coupled online with FTIR spectroscopy and differential scanning calorimetry in inert atmosphere (helium). It was stated that the modified materials showed 20 and 50% mass losses at higher temperatures than the non-modified one while 1% mass loss was observed at lower temperatures. Moreover, an analysis of volatile decomposition products was performed.

     

Effect of a bioactive curcumin derivative on DPPC membrane: A DSC and Raman spectroscopy study

Interactions of dimethoxycurcumin (1) a lipophilic bioactive curcumin derivative with dipalmitoyl phosphatidylcholine (DPPC) were investigated. The thermodynamic changes caused by (1) and its location into DPPC lipid bilayers were monitored by differential scanning calorimetry and Raman spectroscopy. The results reveal that (1) influences the thermotropic properties of DPPC lipid membrane causing abolition of the pretransition and broadening of the phase-transition profile and slightly decreases the T_m at increasing concentrations. The Raman height intensity ratios of the peaks I_2935/2880, I_2844/2880 and I_1090/1130 are representative of the interaction of (1) with the alkyl chains and furnish information about the ratio between disorder and order that exists in the conformation of the alkyl chain. The intensity changes of the peak at 715 cm⁻¹ indicates interaction between the choline head group and (1). The Raman spectroscopy results are in agreement with the thermal analysis results. Biologically active lipophilic molecules such as (1) should be studied in terms of their interaction with lipid bilayers prior to the development of advanced lipid carrier systems such as liposomes. The results of these studies provide information on the membrane integrity and physicochemical properties that are essential for the rational design lipidic drug delivery systems.     

侧链含自由基单元的1,4-吡咯并吡咯二酮共轭聚合物的合成和半导体性质研究

合成了两个侧链含有2,2,6,6-四甲基哌啶-1-氧自由基单元(TEMPO)的1,4-吡咯并吡咯二酮(DPP)共轭聚合物PDPP4T-1和PDPP4T-2,并开展了其半导体性质研究。薄膜场效应晶体管器件测试结果显示,相对于不含TEMPO的聚合物PDPP4T,PDPP4T-1和PDPP4T-2的场效应器件性能有所降低,不过,含TEMPO的聚合物器件性能最高仍达到了2.12cm~2·V~(-1)·s~(-1)。进一步通过原子力显微镜和X射线衍射对TEMPO引入后导致性能降低的可能原因进行了研究。     

Synthesis and the effect of alkyl chain length on optoelectronic properties of diarylethene derivatives

Photochromic symmetrical diarylethene derivatives 1a-6a bearing different long alkyl chains at 2-position of thiophene rings have been synthesized and their structures have been determined by single-crystal X-ray diffraction analysis. The effect of alkyl chain length on their optoelectronic properties, such as photochromism in solution as well as in the crystalline phase and electrochemical performance was investigated in detail. These diarylethenes have showed good photochromic behavior both in solution and in the single crystalline phase. Introduction of the long alkyl chains at 2-position of bis(5-formyl-3-thienyl)perfluorocyclopentene increased the absorption coefficients of both open- and closed-ring isomers and induced bathochromic shifts of the maximal wavelength absorption of the closed-ring isomers. The long alkyl chains can also decrease the cyclization/cycloreversion quantum yields and the oxidation potentials. The cyclic voltammetry indicated that the band gap of these diarylethene derivatives was significantly affected by the alkyl chain length.     

New indole trimers as precursors for molecular electronic materials

We have prepared two new C₃-symmetric, substituted-triazatruxene molecules using a facile one-pot trimerisation of 5-carboxyindole and 6-bromoindole in acetic acid using Br₂, giving 2a and 3a, respectively. These were subsequently modified by the addition of six alkyl chains to the N- and carboxyl-positions of 2a giving 2b and three alkyl chains to the N-positions of 3a giving 3b. The new molecules were characterised using cyclic voltammetry, UV/vis and emission spectroscopy, DFT calculations and in the case of 3b, field-effect transistor measurements showing gate-modulated source-drain current. These represent a straightforward route to large polyaromatic molecules with easily-modified side groups and are suitable as building blocks for synthesis of functional molecules for materials.     

Thermotropic liquid–crystalline properties of 4,4′-dialkoxy-3,3′-diaminobiphenyl compounds and their precursors

A series of 4,4?-dialkoxy-3,3?-diaminobiphenyl compounds were synthesised by three-step procedure that involves alkylation, nitration and reduction reactions. Their chemical structures were characterised by FTIR, ¹H and ¹³C spectroscopy and elemental analysis. Their thermotropic liquid–crystalline (LC) properties were examined by a number of experimental techniques including differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), polarising optical microscopy (POM) and variable temperature X-ray diffraction (VT-XRD). The 4,4?-dialkoxy-3,3?-dinitrobipheyl compounds, precursors to the diamine compounds, were also examined for their thermotropic LC properties. POM studies of focal conic textures and VT-XRD of the 3,3?-diaminobiphenyl derivatives having flexible alkyl chains (C₆–C₁₂) exhibited the smectic A (SmA) phase independent of the length of alkyl chains. Similarly, the 3,3?-dinitrobiphenyl derivatives containing alkyl chains C₇, and C₉–C₁₁ exhibit the SmA phase, those containing C₈ formed the smectic C (SmC) phase and C₁₂ formed both the SmA and smectic B (SmB) phases, respectively. The 3,3?-diaminobiphenyl derivatives had excellent thermal stability in the temperature range of 237–329°C, while those of 3,3?-dinitrobiphenyl derivatives were in the temperature range of 270–321°C. The 3,3?-diaminobiphenyl derivatives emitted UV light both in chloroform and acetonitrile.     

Chiral imidazole metalloenzyme models: Synthesis and enantioselective hydrolysis for α-amino acid esters

Chiral imidazole hydrolytic metalloenzyme models with characteristics of chiral centers directly link to imidazole N-atoms and varieties in both alkyl chain length and number of alkyl chains, have been synthesised and investigated for enantioselective hydrolysis of Boc-α-amino acid esters. The result indicates that both hydrolysis rates and enantioselectivities are increased with increases in the alkyl chain length and the number of the alkyl chains in the lipophilic chiral imidazole-type surfactants in many cases. The lipophilic chiral imidazole 4d ((S)-1-hexadecoxy-2-(1-imidazolyl)-propane), which has one long alkyl chain, shows higher hydrolysis rate and enantioselectivity (k_D = 132.5 × 10⁻⁵, k_D/k_L = 5.38), 5d ((S)-1,5-dihexadecoxy-2-(1-imidazolyl)-pentane), which has two long alkyl chains, shows the highest hydrolysis rate and enantioselectivity (k_D = 201.5 × 10⁻⁵, k_D/k_L = 11.72). Additionally, the effects of the metals, the additives, the solvents and the substrates on the hydrolysis rates and enantioselectivities are examined.     

17,17-Dialkyltetrabenzo[a,c,g,i]fluorenes with extremely high solid-state fluorescent quantum yields: relationship between crystal structure and fluorescent properties

Six 17,17-dialkyltetrabenzo[a,c,g,i]fluorenes (dialkylTBFs) 2–7 (methyl to n-hexyl) were prepared by treatment of 17H-tetrabenzo[a,c,g,i]fluorene (TBF) 1 with n-alkyl halides under basic conditions in moderate yields upon column chromatography and recrystallization. All the compounds show intense blue fluorescence in solutions. On the other hand, in the solid state, the fluorescent spectra and the quantum yields (Φ_p) vary with their alkyl chains. In particular, the Φ_p values of 4–7 bearing n-propyl to n-hexyl groups are close to unity, while the fluorescence of 1 is almost quenched. Crystallographic analyses of 2–7 revealed that the TBF moieties have helicene-like chiral structures in the crystals, and that the alkyl groups basically take an all-trans planar conformation. Because the longer alkyl substituents can serve as a spacer to prevent TBF nuclei from aggregation, π–π interactions of the TBF moieties probably play an important role in quenching the solid-state fluorescence. The relationship between the optical properties and molecular arrangements in the crystals are discussed.     

Supermolecular liquid crystals with a six-armed cyclotriphosphazene core: from columnar to cubic phases

New liquid crystals having a non‐conventional structure have been synthesised from a six‐armed cyclotriphosphazene core, [N₃P₃(OC₆H₄OH‐4)₆], which was condensed with polycatenar acids. Reactions were monitored by ³¹P{¹H} and ¹H NMR spectroscopy and the chemical structure of the resulting materials was confirmed by different spectroscopic techniques and mass spectrometry (MALDI‐TOF). Results were in accordance with monodisperse, fully functionalised cyclotriphosphazenes. Thermal and mesomorphic properties were studied by optical microscopy, differential scanning calorimetry and X‐ray diffraction. All of the synthesised phosphazenes, substituted with benzyl ether chains, show a high thermal stability and exhibit mesomorphic properties, which depend on the number and type of alkyl terminal chains located at the periphery of the mesogens. Mesomorphic properties range from Col_h for cph‐A1 and cph‐A2 to a cubic phase detected for cph‐A3 , which has the larger number of alkyl chains. Furthermore, helical order was detected on X‐ray data of cph‐A2 , which has chiral branched chains. Circular dichroism spectra of annealed films at mesophase temperature show a signal attributed to the chiral helical arrangement of the mesogenic chromophores.     

Gelation properties of poly(aryl ether)dendrons bearing long alkyl chains

Poly(aryl ether) dendrons (2) bearing long alkyl chains can undergo physical gelation in various organic solvents, especially alkanes and alcoholic solvents. In contrast, 3,4,5-trialkoxyphenyl derivatives (1), which are the building blocks of the dendrons (2), do not exhibit any gelation properties; thus, revealing the key role of the dendron structure in the aggregation/gelation process. Hansen solubility parameters allow us to gain a detailed understanding of the role of solvent in gelation. Critical gel concentrations, FT-IR spectroscopy, NMR spectroscopy, T _gel measurements, and scanning electron microscopy are used to characterize the gel structures.     

Gallic esters of 4,5-dinitrocatechol as potential building blocks for thermotropic liquid crystals

A series of unsubstituted and 1,4-disubstituted gallic catecholates 1, 6 and 7 as possible candidates for wedge-shaped mesogens were prepared starting from the respective benzene derivatives 2a-c and gallic esters 5a-h. The mesomorphic properties were investigated by DSC. However, only the 4,5-dinitro derivatives 1d,f-h with C₈H₁₇ and C₁₀H₂₁ to C₁₂H₂₅ alkyl side chains displayed mesophases, as evaluated by fluidity and optical anisotropy.     

Luminescence of Silica-Pillared Clays and Gels Derived from Aminofunctional Silanes

Silica-pillared clays were prepared by reacting Na-montmorillonite aqueous suspensions with (3-aminopropyl)triethoxysilane (APTEOS). It was indicated that cubic octamers [NH ₃ ⁺ (CH₂)₃SiO_3/2]₈ derived from APTEOS are intercalated with two different conformations of the alkyl chains. Namely, the cubic octamers are intercalated with the alkyl chains parallel to the silicate layers at low concentration of APTEOS, and then intercalated with the alkyl chains normal to the silicate layers with increase in APTEOS. Gels were prepared from the reaction of APTEOS with acetic acid and by the conventional sol-gel process using (3-aminopropyl)trimethoxysilane (APTMOS). The luminescence spectra of the gel prepared by the sol-gel process and the intercalated clays were similar to that of silica gels. The gel from APTEOS with acetic acid showed broad visible luminescence. The luminescence spectra and the structures of these materials were described.     

Sila-annulated terrylene diimides for balanced ambipolar transporting

The key building blocks, tetrachlorinated terrylene diimides and the targeted sila-annulated terrylene diimides (Si-TDIs and 2Si-TDIs) were synthesized for the first time. Single-crystal analysis verified the almost planar molecular configurations of both Si-TDIs and 2Si-TDIs. They exhibited intriguing optical properties including red-shifted absorption and near-infrared emission properties with excellent fluorescence quantum yields, as well as precisely controlled HOMO/LUMO energy levels by Si-heteroannulation. The single-crystal organic field-effect transistors based on 2Si-TDI 5a featuring long and branched alkyl chains demonstrated well-balanced ambipolar transporting properties with electron/hole mobilities of 0.10/0.18 cm² V⁻¹ s⁻¹.     

Preparation and characterization of new poly(amide–imide) reinforced layer silicate nanocomposite containing N,N′-pyrromellitoyl-bis-l-phenyl acetic acid

Two new samples of poly(amide–imide)/montmorillonite reinforced nanocomposites containing N,N′-pyrromellitoyl-bis-l-phenyl acetic acid moiety in the main chain were synthesized by a convenient solution intercalation technique. Poly(amide–imide) (PAI) 3 as a source of polymer matrix was synthesized by the direct polycondensation reaction of N,N′-pyrromelitoyl-bis-l-phenyl acetic acid 1 with 4,4′-diamino diphenyl ether 2 in the presence of triphenyl phosphite (TPP), CaCl₂, pyridine and N-methyl-2-pyrrolidone (NMP). Morphology and structure of the resulting PAI-nanocomposite films 4a and 4b with 10% and 20% silicate particles were characterized by FTIR spectroscopy, X-ray diffraction (XRD) and scanning electron microscopy (SEM). The effect of clay dispersion and the interaction between clay and polymeric chains on the properties of nanocomposite films were investigated by using UV–vis spectroscopy, thermogravimetric analysis (TGA) and water uptake measurements.     

Mesophase and magnetic behavior in cobalt(II) and iron(II) compounds

The metal complexes with long alkyl chains [Co(C16-terpy)₃](BF₄)₂ (1) and [Fe(C16-terpy)₂](BF₄)₂ (2) were synthesized and the physical properties of the complex were characterized by magnetic susceptibility, Mössbauer spectroscopy, polarizing optical microscopy, differential scanning calorimetry, and X-ray scattering, where C16-terpy is 4′-hexadecyloxy-2,2′:6′,2′′-terpyridine. Variable-temperature magnetic susceptibility measurements and/or Mössbauer studies revealed that the complex 1 exhibited unique spin transition (T_1/2↓ = 217 K and T_1/2↑ = 260 K) induced by structural phase transition, and the complex 2 was in the low-spin state in the temperature region of 5–400 K before the first mesophase transition. The cobalt(II) and iron(II) complexes exhibited liquid-crystal properties in the temperature range of 371–528 K and 466–556 K, respectively. After mesophase transition, the complex 1 exhibited only slight spin transition (T_1/2↓ = 266 K and T_1/2↑ = 279 K), and the complex 2 was in the low-spin state. The compounds with multifunction, i.e., magnetic property and liquid-crystal properties, are important in the development of molecular materials.     

Synthesis and liquid crystalline behavior of azulene-based liquid crystals with 6-hexadecyl substituents on each azulene ring

Hexakis(6-hexadecyl-2-azulenyl)benzene (1b) has been synthesized by Co₂(CO)₈-catalyzed cyclotrimerization reaction of bis(6-hexadecyl-2-azulenyl)acetylene (2b). The mesomorphic behaviors of 1b, 2b, and 6-hexadecyl-2-phenylazulene (3b) were studied by differential scanning calorimetry (DSC), polarizing optical microscopy (POM), and X-ray diffraction (XRD) techniques and their mesomorphic properties were compared with those of their 6-octyl derivatives 1a, 2a, and 3a. Increase of the number of carbon atoms in the peripheral side chains drops the isotropization temperatures of 1b, 2b, and 3b by 56.9 °C, 33 °C, and 23.6 °C, respectively. Additionally, the phase-transition behavior varied with increase of the number of the peripheral chains, as well as decrease of the crystalline-mesophase transition temperatures, except for compound 3b. As the results, spontaneous monodomain homeotropic molecular alignment was revealed by compound 1b in its Col_hd mesophase on non-treated glass substrate, which would be attracted to the application for the device fabrication of molecular materials.     

Tuning the solid-state emission of the analogous GFP chromophore by varying alkyl chains in the imidazolinone ring

New analogues of green fluorescent protein (GFP) chromophore mGFP-Cn (n = 1, 3, 5, 11) with alkyl chains of different lengths in the imidazolinone rings were synthesized and their crystal structures were determined. These GFP-like chromophores are all emissive in the solid state. And the solid-state emission quantum yields of increase by extending the lengths of alkyl chains, owing to the fact that the intermolecular pi-pi interactions are significantly weakened based on their crystal structures.     

Second-order non-linear optical response in LB films for the metal complexes

The complexes with long alkyl chains {[Fe(C₁₆-trz)₃](ClO₄)₂}_n (1), [Fe(C₁₅-BPT)₂(NCS)₂] (2), [Fe(C₁₆-salen)Cl] (3), [Fe(C₁₆-salmmen)Cl] (4), K[Fe(C₁₆-salen)(CN)₂] (5), K[Fe(C₁₆-salmmen)(CN)₂] (6), Na[Fe(C₁₆-salmmen)(CN)₂] (7), [Mn(C₁₆-salen)Cl] (8), [Ni(C₁₆-salen)] (9), [Cu(C₁₆-salen)] (10) were synthesized (C₁₆-trz = 4-hexadecyl-1,2,4-triazole, C₁₅-BPT = N-(3,5-di-2-pyridinyl-4H-1,2,4-triazol-4-yl)-hexadecanecarboxamide, C₁₆-salen = N,N-bis[4-(hexadecyloxy)salicylidene]ethylenediamine, C₁₆-salmmen = N,N′-bis[4-(hexadecyloxy)salicylidene]-1,2-diaminopropane). Langmuir–Blodgett (LB) films of compounds 1–10 were prepared (Scheme 1). The transfers of the molecules from onto the gas–water surface to glass substrate were confirmed by UV–Vis spectra. The second harmonic generation (SHG) were estimated for the LB films formed by the metal complexes. The SHG was observed for the complexes with the long alkyl chains in LB film. The order of the intensity for the SHG related with the number of unpaired d electrons or the d electron configurations.     

Effect of alkyl side chain length on the properties of polyetherimides from molecular simulation combined with experimental results

Three polyetherimides (PEIs) with the same backbone of Ultem 100 but different lengths of the alkyl side chains were simulated by using molecular dynamics and molecular mechanics techniques to investigate the effect of side chain length on their properties and physical mechanism behind. Simulation results, which are consistent to the experimental data, show that PEI‐5 with four methylene units in each alkyl side chain has higher T_g (glass transition temperature) and higher tensile strength, but lower tensile elongation at break than those of PEI‐6 with five and PEI‐8 with seven methylene units in each alkyl side chain. However, unlike the traditional phenomena, conformational analysis provides that PEI‐5 with the highest T_g gives the highest flexibility to the polymer chain, whereas PEI‐8 with the lowest T_g imparts the lowest flexibility resulting from attachment of longer alkyl side chain increase the rigidity of backbone. From the calculated ratio of the accessible volume to the total volume for each system, the highest ratio of PEI‐8 indicates that long alkyl side chains generate more free volume than short side chains, acting as an internal plasticizer in bulk structure. It is the internal plasticizing effect that is predominantly responsible for the abnormal properties, instead of the rigidity from side chains. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 595–599, 2010