THF Solution Research Articles

Synthesis and Investigation of Copolymers of Glycidyl Methacrylate and Methyl Pheophorbide a in a Solution

Copolymers of glycidyl methacrylate and methyl pheophorbide a of different compositions were synthesized by radical copolymerization in toluene and THF solutions. The influence of the nature of the solvent, initial weight ratio of the monomers, and amount of the copolymerization initiator on the yield of the copolymer and its structure, composition, and properties were established. Physicochemical and molecular weight characteristics of the copolymers were determined.

Kinetic Control of Aggregation Shape in Micellar Self-Assembly.

The first steps towards top-down morphology control in micellar self-assembly are introduced. Kinetically stable micelles are formed from block copolymers (BCPs) using continuous flow techniques by turbulent mixing of water with a THF solution of polymers. In this way, particle shape and size can be altered from spheres to ellipsoids solely via tuning of mixing parameters from a single BCP.

A new hydrazone-based colorimetric chemosensor for naked-eye detection of copper ion in aqueous medium

A new hydrazone-based colorimetric Cu2+ chemosensor is synthesized. Its structure was confirmed by single-crystal X-ray diffraction. Its binding properties towards various metal ions are examined through absorption spectroscopy. In aqueous THF solution, the chemosensor exhibits selective recognition towards Cu2+ over other metal ions with a colour change from colourless to pink. The complex formed between the chemosensor and Cu2+ ions forms a 2:1 stoichiometry with an association constant of 2.46 × 108M−2. The analytical detection limit for Cu2+ by the naked eye is as low as 10.0 μM.

Kinetic Control of Aggregation Shape in Micellar Self‐Assembly

AbstractThe first steps towards top‐down morphology control in micellar self‐assembly are introduced. Kinetically stable micelles are formed from block copolymers (BCPs) using continuous flow techniques by turbulent mixing of water with a THF solution of polymers. In this way, particle shape and size can be altered from spheres to ellipsoids solely via tuning of mixing parameters from a single BCP.

Methoxycarbazolyl-disubstituted dibenzofuranes as holes- and electrons-transporting hosts for phosphorescent and TADF-based OLEDs

In the search of universal host materials for organic light emitting diodes a new series of bipolar host materials containing methoxy-substituted carbazoles as the electron-donating and dibenzofuran as an electron-accepting units were designed and synthesized. Different linking topologies and number of methoxy groups attached to carbazolyl moiety were used to understand the impact of the strength of the donor moiety on the thermal, optical, photophysical, electrochemical and electroluminescent properties. The synthesized compounds exhibited relatively high thermal stability with 5% weight loss temperatures exceeding 378 °C and formed molecular glasses with high glass-transition temperatures ranging from 120 to 148 °C. High triplet energy values of 2.86–2.96 eV were estimated for dilute THF solutions at 77K. Hole and electron drift mobilities estimated using time-of-flight technique in solid layers approached 10−4 cm2V−1s−1 at high electric fields exceeding 3.6 × 105 V cm−1. The synthesized methoxy-carbazole based compounds were tested as hosts in electrophosphorescent and TADF organic light-emitting diodes reaching luminance of 53000 cd m−2 and external quantum efficiency of 12.5%, in the best case.

Insights into the Aggregation Behaviour of a Benzoselenadiazole-Based Compound and Generation of White Light Emission.

We have designed and synthesized the benzoselenadiazole (BDS) based donor-acceptor-donor (D-A-D) π-conjugated compound 4,7-di((E)styryl)benzo[2,1,3]selenadiazole (1). A single-crystal study of 1 shows J-type molecular aggregation in the solid state. The crystal packing of 1 shows head-to-head dimeric intermolecular assembly via Se⋅⋅⋅N interactions while staircase-type interlock molecular packing has occurred via Se⋅⋅⋅π interaction. The staircase-type interlock packing of dimeric molecular arrangement induces sheet-type, herringbone type architecture along crystallographic a axis and ab plane via CH⋅⋅⋅π interactions. Interestingly, the J-type aggregation of 1 in solid state changes to H-type aggregation upon UV-irradiation. Moreover, our spectroscopic findings in solution state reveal H-type of aggregation of 1 in 90 % aqueous THF. We have further demonstrated white light emission in the binary mixture of 1 and 1-pyrenemethanol (2) in 90 % aqueous THF. Our study reveals solvent specific co-assembly of H-aggregated 1 and 2 in 90 % aqueous THF solution, which shows white light emissive properties with the Commission Internationale de l'Eclairage (CIE) chromaticity coordinates (0.32, 0.31). The observed white light emission arises mainly due to the combination of red light from H-aggregated 1, blue light from monomeric 2 and green light from excimers of 2.

A multifunctional aggregation-induced emission (AIE)-active fluorescent chemosensor for detection of Zn2+ and Hg2+

An aggregation-induced emission (AIE)-active fluorescent chemosensor based on a tetraphenylethene (TPE) unit has been successfully designed and synthesized. Interestingly, the luminogen could detect Zn2+ selectively in a THF solution with the detection limit of 1.24 × 10−6 mol L−1. Meanwhile, the luminogen could also detect Hg2+ selectively in a THF-water mixture with the water content of 90%, and the detection limit was 2.55 × 10−9 mol L−1. Furthermore, the solid-state mechanochromic fluorescence behavior of the luminogen was investigated systematically. Indeed, the AIE-active luminogen also exhibited reversible mechanofluorochromic phenomenon involving fluorescent color change from blue to green, and powder X-ray diffraction results indicated that the switchable morphology conversion between crystalline and amorphous states was responsible for this mechanochromism phenomenon.

Mechanical and Morphological Properties of Waterborne ABA Hard-Soft-Hard Block Copolymers Synthesized by Means of RAFT Miniemulsion Polymerization.

High molecular weight waterborne ABA block copolymers of styrene (St) and 2-ethylhexyl acrylate (2EHA) containing hard and soft domains were synthesized by means of RAFT (mini)emulsion polymerization using a bifunctional symmetric S,S-dibenzyl trithiocarbonate (DBTTC) RAFT agent. Miniemulsion polymerization was initially used for the synthesis of the A-block, which forms hard domains, followed by 2EHA pre-emulsion feeding to build the B-block soft domains. Polymerization kinetics and the evolution of the Molecular Weight Distribution (MWD) were followed during the synthesis of different ABA block copolymers. The thermal properties of the final symmetric block copolymers were studied on dried films by means of DSC. It was found that the block copolymers have two glass transitions, which indicates the presence of a two-phase system. Phase separation was investigated by means of microscopic techniques (AFM and TEM) and SAXS, both of the particles in the latex form, as well as after film formation at room temperature and after different post-treatments. Films were annealed at temperatures well above the glass transition temperature (Tg) of the hard phase to study the bulk morphology of the films after complete particle coalescence. Moreover, for comparison purposes, the films were re-dissolved in THF, and films were again cast directly from the homogeneous THF solutions. As THF is a good solvent for both blocks, such films serve as a reference for the equilibrium morphology. Finally, DMTA studies of the films annealed at different temperatures were performed to correlate the morphology changes with the mechanical properties of the block copolymers.

Synthesis, liquid crystalline and gelation properties of 4-semifluoroalkoxybiphenyl derivatives

4-Semifluoroalkoxybiphenyl derivatives 1 and 2(n) (n = 4–6, 8 and 10) were designed, synthesized and their physic-chemical properties were examined. The effects of chemical structure on liquid crystalline and gelation properties were investigated. The clear point for 2(n) declines as the carbon number of terminal alkoxyl chain enlarges from 4 to 10. The clear point for 2(4) is 172 °C while 2(10) is 135 °C. The gelation properties for 2(n) are superior to those for 1, where the linking group of gelators 2(n) between a perfluoroalkyl group and biphenyl core are longer than that of 1. In compounds 2(n), the longer alkoxyl chain at the terminal position, the better gelation properties. The phase selective property of compound 2(10) in THF solution is better than in toluene. 10 wt% 2(10) solution in THF can selectively gelatinize oils and amines from aqueous-organic biphasic mixtures. Interestingly, 10 wt% 2(10) solution in THF also selectively gelatinize organic compound from homogeneous aqueous-organic mixtures. Gels formed by compounds 2(n) as supramolecular gels were investigated their thermoreversible and rheological property.

Spherical Amorphous Nanoparticles from Birch Bark Triterpenoids: Study of the Conditions for the Formation

Triterpenoids from birch bark are valuable biologically active substances. They exhibit important biological properties. However, triterpenoids are insoluble in water due to their hydrophobicity. In order to increase their bioavailability we developed a technique for obtaining spherical amorphous nanoparticles (SANP) by their precipitation with water from a solution in THF. In the form of nanoparticles, triterpenoids show additional useful properties: they can be loaded with hydrophobic substances. SANP were also shown to be effective immunological adjuvants. This article is devoted to the study of conditions that could optimize their production. As a result, it was shown that among the three investigated solvents miscible with water - acetone, dioxane, THF -the latter gives the best results. Lowering temperature decreases the size of SANP. An increased temperature leads to the formation of betulin crystals. When the concentration of triterpenoids in THF is higher than 5 mg/ml, crystals of betulin also begin to form. The results of this study lead to the assumption that the main parameter of the process determining the formation of SANP is the rate of the solvent diffusion into water.

Fluorescence and Rotational Dynamics of a Crystalline Molecular Rotor Featuring an Aggregation-Induced Emission Fluorophore.

Recent studies have shown that "crystal fluidity" in the form of fast conformational motions is critical for large-amplitude rotational motion in crystals. To explore this concept, we designed a crystalline assembly featuring two diethynylbenzene (DEB) molecular rotators linked to tetraphenylethylene (TPE), a fluorophore known to emit with intensities that depend on the rigidity of the medium. We envisioned that an increase in crystal fluidity as a function of increasing temperature would facilitate rotational motion of the DEB while diminishing the fluorescence intensity of the TPE. The aggregation-induced emission of the TPE moiety was confirmed when its fluorescence intensity increased by the addition of water to a THF solution. While bulk solids showed a relatively strong TPE emission with a lifetime of 4 ± 1 ns, no significant changes were observed between measurements carried out from 77 to 298 K, indicating that the crystal environment has limited motion within the excited-state lifetime. This conclusion was confirmed by the quadrupolar echo 2H NMR line-shape analysis of a deuterium-labeled sample between 198 and 298 K, which revealed rotational correlation times in the microsecond regime, suggesting that rotational fluidity is 3 orders of magnitude too slow to affect fluorescence emission.

Systematical Study of the Stabilization and Electrochemical Behavior of Li and Mg Polysulfides

Magnesium-based chemistries are of high interest to the battery research community because of the high capacity and abundance of the Mg as anode material. Although providing a high anode capacity, the bivalency of the Mg cation is also the bottleneck of Mg-based batteries. The solid-state diffusion of the highly charged, small Mg2+-ion is accompanied by high activation energies limiting the choice of insertion cathode materials with reasonable cell voltages and capacities. In contrast, the conversion-type sulfur cathode has been demonstrated as a promising cathode material to be combined with the magnesium electrode. As intensively investigated in Li/S cells, also in Mg/S batteries one key issue is the emergence of bivalent Sx 2− and radical Sy ●− polysulfide intermediates during charge/discharge. The diffusion of these polysulfides into the electrolyte leads to capacity fading at the cathode and side reactions at the metal anode. These species thus have a great influence on the cycling performance of the respective cells. In a systematical study, the fundamental electrochemical behavior as well as the solubility and stabilization of Li and Mg polysulfides was investigated in a broad variety of solvents. Thereby, we focused on the solvent-depending influence of Li+ and Mg2+ cations on the polysulfide species. Firstly, the disproportionation and dissociation equilibria of “Li2S8“ and “MgS8” in DMSO, DMF, ACN, THF, DME, TEGDME, and Pyr14TFSI solutions were investigated via UV/Vis spectroscopy.[1] The findings were combined with methodic quantum chemical calculations of the stability of the individual polysulfide species in these solutions. Thereby, also the influence of LiTFSI and MgTFSI2 was examined. Secondly, the influence of the solvent and cation-coordination on the electrochemical behavior was studied in cyclic voltammetry measurements. It could be shown that the stabilization of different polysulfide species is not only determined by the solvents’ relative dielectric permittivity and donor number, but also depends on the coordination by either Li+ or Mg2+ cations in a mutual interplay with the solvent. This interplay will be presented to be essential for the reactions and occurring overpotentials and therefore gives insight in the role of the cation in determining the charge and discharge mechanism of the sulfur cathode.[1,2] Acknowledgement: German Federal Ministry for Education and Research ‘MgMeAnS’ (03XP0140).

Potential‐Energy Surface and Dynamics Simulation of THBDBA: An Annulated Tetraphenylethene Derivative Combining Aggregation‐Induced Emission and Switch Behavior

AbstractElectronic structure calculations and nonadiabatic dynamics simulations were carried out on the excited state decay mechanism of a typical aggregation‐induced emission (AIE)‐active molecule, 10,10′,11,11′‐tetrahydro‐5,5′‐bidibenzo[a,d][7]annulenylidene (THBDBA), which was experimentally found to be almost non‐emissive in THF solution but highly luminescent as an aggregate. At the MS‐CASPT2//CASSCF level, the decay path from S1 leads to a conical intersection (CI) seam with the ground state (S0) via a cyclization process of two neighboring phenyl groups. Nonadiabatic dynamics simulations of 367 surface hopping trajectories show that all the structures of hopping points resemble those of the S1/S0 CI seam with cyclized geometry. The final structures of trajectories hopping to S0 belong to either Franck‐Condon (FC) like structures (66.8 %) or cyclized conformers (33.2 %), which agrees well with the experimental result of 23 % cyclization product (Y. Cai et al. Chem. Sci., 2011, 2, 2029–2034). Our results also indicate that long‐time irradiation leads to a photostationary state where the open and cyclized forms interconvert photochemically. The preference for photocyclization over double bond isomerization is due to the rigidity of the dihydrofulvene rings. From the point of view of AIE, the calculations suggest that THBDBA follows our restricted access to a CI (RACI) model because the photocyclization requires large displacements of the phenyl rings. These displacements must be blocked in the aggregate phase, inhibiting the decay and leading to luminescence. Our study contributes to understand the AIE and switch behavior of THBDBA and will be useful to support the design of new molecules with these features.

Selective and facile deacetylation of pentacyclic triterpenoid under methanolic ammonia condition and unambiguous NMR analysis

The acetyl ester plays an important role for protection of the hydroxyl groups in carbohydrates synthesis. In the present study, we described an efficient deprotection of acetyl group of pentacyclic triterpenoid by using methanolic ammonia in THF solution. Good selectivity for cleaving gal-C2-OAc group of 3β-hydroxy-olean-12-en-28-oic acid 28-N-2,3,4,6-tetra-O-acetyl-β-d-galactopyranoside (3) was achieved in the presence of methanolic ammonia within 4 h at low temperature (−60 °C) in a yield of 56%. The reaction disclosed here provides a new method for the synthesis of C2 selective modified carbohydrates, which is more useful than conventional synthesis procedure that usually requires many steps including temporary regioselective protection and deprotection. When the reaction temperature was increased from −60 °C to room temperature, the cleavage of the other three acetyl groups of galactose in an order of C4-OAc > C3-OAc > C6-OAc was observed. Based on this study, a plausible route for the deacetylation reaction has been proposed.

Neodymium–Dysprosium and Neodymium–Ytterbium Iodide–Sulfide–Nitride Clusters: Synthesis and Luminescence

Heterolanthanide clusters Nd2LnI5(S3)(S2N2)(THF)9 (Ln = Dy, Yb) are synthesized by the reactions of (NdI)3N2 with DyI3 or YbI3 and sulfur in a THF solution. X-ray diffraction analysis revealed that the structure of the complexes is similar to the structure of Nd2LnI5(S3)(S2N2)(THF) 9 obtained earlier (Ln = Tb, Tm). The ion Dy3 + in the molecule is coordinated by the iodine atom, the S2 group and the terminal N atom in the resulting S3N2 ligand. Cluster Nd2YbI5(S3)(S2N2)(THF)9 of the same structure was obtained as well when YbI2 was used instead of YbI3. Possible pathways of the reactions are discussed. UV excitation of Nd2DyI5(S3)(S2N2)(THF)9 causes low-intensity emission of Dy3+ ions: two bands at 480 and 580 nm. Magnetic measurements showed no exchange interaction in the obtained clusters.

Trapping of trifluoroacetonitrile imines with mercaptoacetaldehyde and mercaptocarboxylic acids: An access to fluorinated 1,3,4-thiadiazine derivatives via (3+3)-annulation

The in situ generated highly electrophilic nitrile imines derived from trifluoroacetonitrile are efficiently trapped by monomeric mercaptoacetaldehyde at room temperature in THF solution. The initially formed 1:1 adducts undergo spontaneous cyclization leading to 6-membered 5,6-dihydro-1,3,4-thiadiazin-5-ols bearing the CF3 group at the C(2) atom in good yields. Subsequent oxidation of the latter products using C5H5N∙HCl∙CrO3 (PCC) led smoothly to the expected 1,3,4-thiadiazin-5-ones as final products. Alternatively, analogous 2-trifluoromethylated heterocycles were obtained via trapping of the same nitrile imines with α-mercaptocarboxylic acids followed by 1-[3-(dimethylamino)propyl]-3-ethylcarbodiimide methiodide (EDC methiodide) induced cyclisation of the initially formed 1:1 adducts. In general, efficiency of the second approach was lower and depended on the type of substituent attached to phenyl ring in the starting 1,3-dipole.

Synthesis of Conjugated Polymers Containing Diketopyrrolopyrrole (DPP) Building Block and the Photophysical Study

Sonogashira coupling of two different diketopyrrolopyrrole (DPP)-containing dihaloarenes with the same aromatic bisalkyne resulted in two new conjugated polymers with the same backbone but different pendant groups on the DPP moiety. The polymers were found to have designed chemical structures via structural characterizations in comparison with three monomers. The molecular weight measurement further demonstrated the formation of polymers with polydispersity index around 2, consistent with the polycondensation nature of the polymerization based on Sonogashira coupling. Both polymers could dissolve in many organic solvents, and the one with long alkyl side group on DPP moiety had better solubility. Photophysical investigation showed that both polymers had typical absorption/emission of conjugated polymers, and varying the solvent did not have large influence. Compared with other polar solvents, toluene reduced the quantum yield of fluorescence of the polymers, especially for the one with long alkyl pedant group, accompanying with slight red-shift in absorption/emission. The difference in the absorption/emission wavelengths between the polymers was similar to that between the corresponding monomers. Adding water into the THF solution of polymers reduced the emission intensity but no redshift was observed. Discussion about the structure-property relationships was carried out in detail.

Optoelectronic, Aggregation, and Redox Properties of Double-Rotor Boron Difluoride Hydrazone Dyes.

We develop the chemistry of boron difluoride hydrazone dyes (BODIHYs) bearing two aryl substituents and explore their properties. The low-energy absorption bands (λmax =427-464 nm) of these dyes depend on the nature of the N-aryl groups appended to the BODIHY framework. Electron-donating and extended π-conjugated groups cause a redshift, whereas electron-withdrawing groups result in a blueshift. The title compounds were weakly photoluminescent in solution and strongly photoluminescent as thin films (λPL =525-578 nm) with quantum yields of up to 18 % and lifetimes of 1.1-1.7 ns, consistent with the dominant radiative decay through fluorescence. Addition of water to THF solutions of the BODIHYs studied causes molecular aggregation which restricts intramolecular motion and thereby enhances photoluminescence. The observed photoluminescence of BODIHY thin films is likely facilitated by a similar molecular packing effect. Finally, cyclic voltammetry studies confirmed that BODIHY derivatives bearing para-substituted N-aryl groups could be reversibly oxidized (Eox1 =0.62-1.02 V vs. Fc/Fc+ ) to their radical cation forms. Chemical oxidation studies confirmed that para-substituents at the N-aryl groups are required to circumvent radical decomposition pathways. Our findings provide new opportunities and guiding principles for the design of sought-after multifunctional boron difluoride complexes that are photoluminescent in the solid state.

A silicon-cored tetraphenyl benzene derivative with aggregation-induced emission enhancement as a fluorescent probe for nitroaromatic compounds detection.

Two benzene with multiple contiguous phenyl substituent derivatives, namely, 1, 2, 3, 4-tetraphenyl benzene (TPB) and bis(1,2,3,4-tetraphenylbenzene-yl) diphenylsilane (TPB-Si), were synthesized by the Knoevenagel/Diels-Alder method. TPB and TPB-Si both showed aggregation-induced emission enhancement (AIEE) properties in tetrahydrofuran/water mixtures. The fluorescence-quenching behaviors of the two compounds with different nitroaromatic compounds were also investigated. TPB and TPB-Si both showed low detection limit, high sensitivity, and high quenching efficiency in detecting nitroaromatic compounds. Furthermore, the two compounds in aggregate state exhibited much better detection abilities than in THF solution. And TPB-Si exhibited better detection ability than TPB in both solution and aggregate state. The reason could be attributed to the special tetrahedral molecular structure of TPB-Si, which was demonstrated by theoretical calculations and crystal structures. Moreover, TPB-Si in solid film also exhibited excellent detection performance to nitroaromatic explosive vapor. This work may serve as a basis for designing new organic materials with great efficiency and sensitivity in fluorescence detection.

Grinding-Triggered Single Crystal-to-Single Crystal Transformation of a Zinc(II) Complex: Mechanochromic Luminescence and Aggregation-Induced Emission Properties.

We first report single crystal X-ray analysis of ground crystals of mechanochromic luminescence (MCL) that shows single crystal-to-single crystal transformation (SCSCT). Single crystals of [ZnL2] (1-SG, HL = 2-[[[4-(2-benzoxazolyl)phenyl]imino]-methyl]-5-(diethylamino)-phenol) were obtained upon slight grinding of single crystals of [ZnL2]·0.5CH3OH (1), both of which were characterized by single crystal X-ray diffraction. Crystals of 1 showed emission centered at 647 nm (red color), while crystals of 1-SG showed emission band at 624 nm (orange-red color) under UV light, indicating MCL property of the Zn(II) complex. Reversible MCL property with emission color change between red and yellow for 1 was observed upon high grinding and recrystallization. Single crystal X-ray analysis suggested that it is due to the alteration of molecular conformation of ligands in ZnL2 instead of weak intermolecular interaction that 1 exhibits MCL. Investigation of the control Zn(II) complexes (2-4) indicated that flexible substituents and rotated aromatic rings are desirable to generate the MCL-active complexes. In addition, 1 was highly fluorescent in THF solution, but its fluorescence quenched upon addition of water. DFT calculations suggested that this is due to the formation of the excited hydrated ZnL2 species via Zn-O coordination bond, which results in electron-driven proton transfer (EDPT). Aggregates formed as water fraction ( fw) in THF/H2O (v/v) reached 70%, and fluorescence emission was enhanced. This phenomenon continued until fw was 90%, indicating aggregation-induced emission (AIE) property. The mechanism of AIE of ZnL2 in THF/H2O is the restriction of intramolecular rotation (RIR).