Bulky Methyl Research Articles

Controlling Reactivity through Spin Manipulation: Steric Bulkiness of Peroxocobalt(III) Complexes.

The intrinsic relationship between spin states and reactivity in peroxocobalt(III) complexes was investigated, specifically focusing on the influence of steric modulation on supporting ligands. Together with the previously reported [CoIII(TBDAP)(O2)]+ (2Tb), which exhibits spin crossover characteristics, two peroxocobalt(III) complexes, [CoIII(MDAP)(O2)]+ (2Me) and [CoIII(ADDAP)(O2)]+ (2Ad), bearing pyridinophane ligands with distinct N-substituents such as methyl and adamantyl groups, were synthesized and characterized. By manipulating the steric bulkiness of the N-substituents, control of spin states in peroxocobalt(III) complexes was demonstrated through various physicochemical analyses. Notably, 2Ad oxidized the nitriles to generate hydroximatocobalt(III) complexes, while 2Me displayed an inability for such oxidation reactions. Furthermore, both 2Ad and 2Tb exhibited similarities in spectroscopic and geometric features, demonstrating spin crossover behavior between S = 0 and S = 1. The steric bulkiness of the adamantyl and tert-butyl group on the axial amines was attributed to inducing a weak ligand field on the cobalt(III) center. Thus, 2Ad and 2Tb are an S = 1 state under the reaction conditions. In contrast, the less bulky methyl group on the amines of 2Me resulted in an S = 0 state. The redox potential of the peroxocobalt(III) complexes was also influenced by the ligand field arising from the steric bulkiness of the N-substituents in the order of 2Me (-0.01 V) < 2Tb (0.29 V) = 2Ad (0.29 V). Theoretical calculations using DFT supported the experimental observations, providing insights into the electronic structure and emphasizing the importance of the spin state of peroxocobalt(III) complexes in nitrile activation.

Impact of ligand substituents on the spiral arrangement in glutarohydrazide-based binuclear-iron(II) helicates

Coordination-driven self-assembly, particularly, helical metal complexes are quite interesting considering their distinctive architectures. Herein, we assemble new Fe(II) compounds namely, [Fe2(L1)2](BF4)4·2H2O, 1 and [Fe2(L2)2](BF4)4, 2 from flexible glutarohydazide ligands featuring helical-like di-nuclear arrays. Structurally, in all the compounds, the two chelating ligands were arranged differently, i.e. inverted U-shaped conformation for 1 and a twisted spiral arrangement for 2 were observed respectively. Interestingly, the observed structural variations of all compounds are a result of the ligand substituents in the six positions of the pyridyl moiety in which the relatively bulky methyl group substituted ligand resists the spiral arrangement which was observed in the Br substituted analog. Magnetic investigations revealed that compounds 1 and 2 are in the high spin state at all the measured temperature ranges. Further ligand fine-tunings in the pyridyl-aldehyde moiety for the presented helical-like arrays bearing relatively strong ligand field strength are suggested for achieving the spin crossover (SCO) event.

Eutectic Mixtures As Highly Concentrated and Molten Electrolytes with Nearly Single-Ion Conducting Behavior

Today's state-of-the-art liquid electrolytes in lithium ion batteries (LIBs) have a high ionic conductivity and good performance regarding their cycle life. (1) However, they pose a safety risk due to their high vapor pressures and low thermal stability. (1) Furthermore, due to the limited electrochemical stability of the solvent, liquid electrolytes are not suitable for the application in high-voltage LIBs. (2) Molten salts, also called ionic liquids (IL), or highly concentrated electrolytes (HCE) have high lithium ion concentrations, where nearly every solvent molecule is coordinated. Due to this, there are strong ion interactions and the formation of ion clusters that lead to an increased lithium ion transference number of >0.5. (3) Therefore, they can represent an alternative in the field of liquid electrolytes. Additionally, HCE exhibit a higher thermal and electrochemical stability compared to dilute electrolytes and can improve the cycle performance in lithium metal batteries. (4, 5)McOwen et al. reported the coordination of lithium ions and crystalline structures in HCE of the binary mixtures of ethylene carbonate (EC) and lithium bis(trifluoromethane sulfonyl)imide (LiTFSI) with molar ratio up to 1:1. (6) Based on the concept of melting point depression as known from thermodynamics, room-temperature molten, highly concentrated electrolytes of a carbonate-based solvent with lithium sulfonyl imides were investigated. Instead of EC, the solvent pinacol carbonate (PIC) without acidic α-hydrogen atoms, but four bulky methyl groups was synthesized and used for eutectic mixtures, as the melting point of PIC is with 187 °C far above room-temperature. The physicochemical properties of these electrolytes are studied with respect to the different influence of lithium bis(fluorosulfonyl)imide and LiTFSI despite their same basic molecule structure. The focus will be on the electrochemical analysis by the means of the ionic conductivity, transference number and the electrochemical stability.In comparison to dilute liquid electrolytes the molten electrolytes show extremely high transference numbers, especially for the PIC-LiTFSI mixtures nearly a single-ion conducting behavior (0.9) is observed. This behavior can be explained by the formation of a 2D polymeric network within the HCE electrolyte as determined by crystallographic measurements in the solid state. Combined with the high electrochemical stability, a stable long-term cycling and dendrite suppression in symmetric lithium cells could be shown. Cycling in full cells with high-voltage cathode materials such as LiNi0.6Mn0.2Co0.2O2 (NMC622) or LiMn4O2 (LMO) against lithium metal anodes is applicable. References K. Xu, Chemical Reviews, 104(10), 4303–4417 (2004).J. Li, C. Ma, M. Chi, C. Liang and N. J. Dudney, Advanced Energy Materials, 5(4) (2015).K. M. Diederichsen, E. J. McShane and B. D. McCloskey, ACS ENERGY LETTERS, 2(11), 2563–2575 (2017).G. Jiang, F. Li, H. Wang, M. Wu, S. Qi, X. Liu, S. Yang and J. Ma, Small Struct., 2(5), 2000122 (2021).V. Nilsson, A. Kotronia, M. Lacey, K. Edstrom and P. Johansson, ACS Applied Energy Materials, 3(1), 200–207 (2020).D. W. McOwen, D. M. Seo, O. Borodin, J. Vatamanu, P. D. Boyle and W. A. Henderson, Energy & Environmental science, 7(1), 416–426 (2014).

BODIPY doping of covalent organic frameworks-based nanomaterials: A novel strategy towards biomedical applications

Covalent organic Frameworks (COFs) are a class of crystalline macromolecular materials build-up by monomers with specific symmetries or functionalities. There are important limitations in the synthesis of highly ordered COFs, such as the shape and packing of the building blocks. Thus, the presence of fluorine atoms that lie perpendicular to the bisecting plane of BODIPY derivatives together with the presence of four bulky methyl groups could hinder the crystallization process in COF synthesis. For that reason, BODIPY-based COFs are rarely incorporated to COF networks. In this work, following the mixed linker strategy, a pre-synthetic method to dope COF structures with BODIPY units was developed. The materials have been processed into fluorescent Covalent Organic Nanosheets (CONs) with defined particle-size distributions around 100 nm, suitable for cellular biomedical applications. The viability of the CONs was evaluated using Sk-Mel-103 cells, demonstrating the internalization showing 100% cell viability. We envisage that this work could accelerate the discovery of new COF-based materials for biomedical sciences.

Comparative electroanalytical performance of poly o‐toulidine and polyaniline towards hydrazine oxidation supplemented by DFT

AbstractThis work presents a comparative experimental and theoretical study on the use of polyaniline and its derivative, poly o‐toluidine, as effective electrochemical sensor for the detection of hydrazine. Hydrazine is a toxic analytic with numerous adverse health effects on the human brain, liver and nervous system. The conducting polymers polyaniline (PANI) and poly o‐toluidine (POT) were synthesized by oxidative polymerization and characterized through x‐ray Diffraction, FT‐IR, and UV–Visible Spectroscopy. Electrochemical studies performed on the polymer modified glassy carbon electrode (GCE) using cyclic voltammetry and differential pulse voltammetry reveal strong interaction between hydrazine and the polymer through irreversible charge transfer. The oxidation current was seen to increase with increasing hydrazine concentration. The diffusion coefficients were found to be 1.89 × 10−5 cm2/s and 2.89 × 10−6 cm2/s for PANI and POT, respectively. PANI and POT based sensors show a limit of detection of 1 μM and 5.13 mM, respectively in the linear concentration range of 1–9 mM. Density functional studies on the PANI‐hydrazine and POT‐hydrazine complexes show enhanced intermolecular charge transfer from nitrogen lone pairs in hydrazine to the polymer backbone clearly identifying the donor and acceptor moieties. PANI based electrochemical sensor is shown to have a higher sensitivity for hydrazine compared to POT, where the sensing interaction is hindered by the bulky methyl group in ortho position.

Ortho Effects of Tricarboxylate Linkers in Regulating Topologies of Rare-Earth Metal-Organic Frameworks.

A linker design strategy is developed to attain novel polynuclear rare-earth (RE) metal-organic frameworks (MOFs) with unprecedented topologies. We uncover the critical role of ortho-functionalized tricarboxylate ligands in directing the construction of highly connected RE MOFs. The acidity and conformation of the tricarboxylate linkers were altered by substituting with diverse functional groups at the ortho position of the carboxyl groups. For instance, the acidity difference between carboxylate moieties resulted in forming three hexanuclear RE MOFs with novel (3,3,3,10,10)-c wxl, (3,12)-c gmx, and (3,3,3,12)-c joe topologies, respectively. In addition, when a bulky methyl group was introduced, the incompatibility between the net topology and ligand conformation guided the co-appearance of hexanuclear and tetranuclear clusters, generating a novel 3-periodic MOF with a (3,3,8,10)-c kyw net. Interestingly, a fluoro-functionalized linker prompted the formation of two unusual trinuclear clusters and produced a MOF with a fascinating (3,8,10)-c lfg topology, which could be gradually replaced by a more stable tetranuclear MOF with a new (3,12)-c lee topology with extended reaction time. This work enriches the polynuclear clusters library of RE MOFs and unveils new opportunities to construct MOFs with unprecedented structural complexity and vast application potential.

Shape-Persistent Liquid Crystal Elastomers with Cis-Stable Crosslinkers Containing Ortho-Methyl-Substituted Azobenzene

Shape-persistent cis-isomer-stable azobenzene-functionalized liquid crystal elastomers (azo-LCEs) were prepared using an azobenzene crosslinker with two methyl substitutions at the ortho positions of azobenzene [4,4′-di(4-(acrylolylhexyloxy) benzoyloxy)-2,6-dimethylazobenzene (DADO)] via thiol–acrylate Michael addition photopolymerization. Ultraviolet–visible (UV–vis) and nuclear magnetic resonance (NMR) spectroscopies revealed that the methyl substituents on DADO rocked its cis conformation under UV irradiation and significantly delayed the visible (laser)-light-induced cis-to-trans isomerization. Raman spectroscopy and small-/wide-angle X-ray scattering analyses indicated that the cis-isomers in DADO-linkage-containing monodomain azo-LCE (azo-MLCEDADO) were not readily converted to the trans conformation under visible (laser)-light irradiation but transformed easily upon mechanical drawing. The azo-MLCEDADO film exhibited a low-plateau modulus and high elongation because of the weak intermolecular interactions caused by its bulky methyl substituents, leading to considerable UV-irradiation-induced contraction (up to 50%) and suspended weight-induced recovery to its original length. These cis-stable azo-MLCEDADO films can be used in shape-persistent actuators in soft robotics, haptics, and biomedical device fabrication.

Novel organo-soluble poly(ether imide)s based on diethyltoluenediamine: Synthesis, characterization and gas transport properties

Novel dianhydrides containing bromine substituents were developed. Series of poly(ether imide)s (PEIs) using diethyltoluenediamine (DETDA) and several bis(ether anhydride)s containing bulky methyl, cyclohexylidene, isopropylidene, hexafluoroisopropylidene and bromine fragments was prepared by one-pot synthesis in benzoic acid. Chemical structures were confirmed by FT-IR and 1H NMR spectroscopy. All PEIs demonstrated great solubility in organic solvents. The weight-average molecular weight (Mw) of the polymers were in the range of 6.1–11.3 × 104 g/mol. PEIs showed glass transition temperature in the range of 285–315 °C according to DSC. Furthermore, PEIs demonstrated great thermal stability with degradation temperature (Td5%) higher 432 °C. Polymer films have good mechanical properties with tensile strength up to 91.6 MPa and elongation at break up to 89.4%. Correlation between the chemical structure and gas transport properties was investigated.

Steric Effects in the Deposition Mode and Drug-Delivering Efficiency of Nanocapsule-Based Multilayer Films.

Using surface-initiated atom transfer radical polymerization (ATRP), block polymers with a series of quaternization degrees were coated on the surface of silica nanocapsules (SNCs) by the “grafting-from” technique. Molnupiravir, an antiviral medicine urgently approved for the treatment of SARS-CoV-2, was encapsulated in polymer-coated SNCs and further incorporated into well-defined films with polystyrene sulfonate (PSS) homopolymers by layer-by-layer (LBL) self-assembly via electrostatic interactions. We investigated the impact of the quaternization degree of the polymers and steric hindrance of functional groups on the growth mode, swelling/deswelling transition, and drug-delivering efficiency of the obtained LBL films. The SNCs were derived from coronas of parent block polymers of matched molecular weights—poly(N-isopropylacrylamide)-block-poly(N,N-dimethylaminoethyl methacrylate) (PNIPAM-b-PDMAEMA)—by quaternization with methyl sulfate. As revealed by the data results, SNCs with coronas with higher quaternization degrees resulted in a larger layering distance of the film structure because of weaker ionic pairing (due to the presence of a bulky methyl spacer) between SNCs and PSS. Interestingly, when comparing the drug release profile of the encapsulated drugs from SNC-based films, the release rate was slower in the case of capsule coronas with higher quaternization degrees because of the larger diffusion distance of the encapsulated drugs and stronger hydrophobic–hydrophobic interactions between SNCs and drug molecules.

Reversing RAFT Polymerization: Near-Quantitative Monomer Generation Via a Catalyst-Free Depolymerization Approach.

The ability to reverse controlled radical polymerization and regenerate the monomer would be highly beneficial for both fundamental research and applications, yet this has remained very challenging to achieve. Herein, we report a near-quantitative (up to 92%) and catalyst-free depolymerization of various linear, bulky, cross-linked, and functional polymethacrylates made by reversible addition–fragmentation chain-transfer (RAFT) polymerization. Key to our approach is to exploit the high end-group fidelity of RAFT polymers to generate chain-end radicals at 120 °C. These radicals trigger a rapid unzipping of both conventional (e.g., poly(methyl methacrylate)) and bulky (e.g., poly(oligo(ethylene glycol) methyl ether methacrylate)) polymers. Importantly, the depolymerization product can be utilized to either reconstruct the linear polymer or create an entirely new insoluble gel that can also be subjected to depolymerization. This work expands the potential of polymers made by controlled radical polymerization, pushes the boundaries of depolymerization, offers intriguing mechanistic aspects, and enables new applications.

Supramolecular Helical Assemblies of Dirhodium(II) Paddlewheels with 1,4-Diazabicyclo[2.2.2]octane: A Remarkable Substituent Effect on the Helical Sense Preference and Amplification of the Helical Handedness Excess of Metallo-Supramolecular Helical Polymers.

We report unique coordination-driven supramolecular helical assemblies of a series of dirhodium(II) tetracarboxylate paddlewheels bearing chiral phenyl- or methyl-substituted amide-bound m-terphenyl residues with triethylene glycol monomethyl ether (TEG) or n-dodecyl tails through a 1:1 complexation with 1,4-diazabicyclo[2.2.2]octane (DABCO). The chiral dirhodium complexes with DABCO in CHCl3/n-hexane (1:1) form one-handed helical coordination polymers with a controlled propeller chirality at the m-terphenyl groups, which are stabilized by intermolecular hydrogen-bonding networks between the adjacent amide groups at the periphery mainly via a cooperative nucleation-elongation mechanism as supported by circular dichroism (CD), vibrational CD, and variable-temperature (VT) absorption and CD analyses. The VT visible-absorption titrations revealed the temperature-dependent changes in the degree of polymerization. The columnar supramolecular helical structures were elucidated by X-ray diffraction and atomic force microscopy. The helix sense of the homopolymer carrying the bulky phenyl and n-dodecyl substituents is opposite those of other chiral homopolymers despite having the same absolute configuration at the pendants. A remarkably strong "sergeants and soldiers" (S&S) effect was observed in most of the chiral/achiral copolymers, while the copolymers of the bulky chiral phenyl-substituted dirhodium complexes with n-dodecyl chains displayed an "abnormal" S&S effect accompanied by an inversion of the helix sense, which could be switched to a "normal" S&S effect by changing the solvent composition. A nonracemic dirhodium complex of 20% enantiomeric excess bearing the less bulky chiral methyl substituents with n-dodecyl chains assembled with DABCO to form an almost one-handed helix (the "majority rule" (MR) effect), whereas the three other nonracemic copolymers showed a weak MR effect.

Tracking excited state decay mechanisms of pyrimidine nucleosides in real time

DNA owes its remarkable photostability to its building blocks—the nucleosides—that efficiently dissipate the energy acquired upon ultraviolet light absorption. The mechanism occurring on a sub-picosecond time scale has been a matter of intense debate. Here we combine sub-30-fs transient absorption spectroscopy experiments with broad spectral coverage and state-of-the-art mixed quantum-classical dynamics with spectral signal simulations to resolve the early steps of the deactivation mechanisms of uridine (Urd) and 5-methyluridine (5mUrd) in aqueous solution. We track the wave packet motion from the Franck-Condon region to the conical intersections (CIs) with the ground state and observe spectral signatures of excited-state vibrational modes. 5mUrd exhibits an order of magnitude longer lifetime with respect to Urd due to the solvent reorganization needed to facilitate bulky methyl group motions leading to the CI. This activates potentially lesion-inducing dynamics such as ring opening. Involvement of the 1nπ* state is found to be negligible.

Effects of β-bromine substitution and core protonation on photosensitizing properties of porphyrins: Long wavelength photosensitizers

In this study, a series of β-brominated meso-tetraphenylporphyrins, H2TPPBrx (x = 2, 4, 6 and 8) with remarkably red shifted absorption bands towards the longer wavelengths of the visible light known as therapeutic window and their diprotonated analogues were used as photosensitizers in the aerobic oxidation of cyclooctene to investigate the influence of degree of β bromination on the photocatalytic activity and oxidative stability of H2TPP. Furthermore, the β brominated porphyrins showed significantly decreased fluorescence quantum yields (φF) and radiative decay rate constants but increased non-radiative decay rate constants. The highest catalytic activity was observed in the case of the partially brominated porphyrins, H2TPPBr2 and H2TPPBr4. While, H2TPPBr2 and H2TPPBr4 were as stable as H2TPP, the oxidative degradation of H2TPPBr6 and H2TPPBr8 was remarkably higher than that of the non-brominated porphyrin. A good correlation was observed between the photocatalytic activity of H2TPPBrx and their diprotonated species and the singlet oxygen quantum yields (ϕΔ = 0.02–0.21 and 0.12 to 0.59, respectively), determined chemically through the reaction of singlet oxygen with 1,3-diphenylisobenzofuran (DPBF). In order to examine the effects of steric hindrance on the photocatalytic properties of the brominated porphyrins, β tetra-brominated derivative of meso-tetra(2-methylphenyl)porphyrin, H2T(2-Me)PPBr4 with bulky methyl substituents at the ortho positions was prepared and compared with H2TPPBr4. The steric hindrance caused by the presence of four methyl groups could improve the oxidative stability of the photosensitizer by 30 to 50% at the cost of significant loss of photocatalytic activity. On the other hand, diprotonation of H2TPPBrx with weak and strong acids (CH2ClCOOH and CF3COOH) was found to be an efficient approach to overcome the extensive oxidative degradation of these photosensitizers, with concomitant red shift of the absorption bands to 451–490 and 674–743 nm, in the Soret and Q band regions, respectively.

Structural basis for the selective addition of an oxygen atom to cyclic ketones by Baeyer-Villiger monooxygenase from Parvibaculum lavamentivorans

Baeyer-Villiger monooxygenase (BVMO) catalyzes insertion of an oxygen atom into aliphatic or cyclic ketones with high regioselectivity. The BVMOs from Parvibaculum lavamentivorans (BVMOParvi) and Oceanicola batsensis (BVMOOcean) are interesting because of their homologies, with >40% sequence identity, and reaction with the same cyclic ketones with a methyl moiety to give different products. The revealed BVMOParvi structure shows that BVMOParvi forms a two-domain structure like other BVMOs. It has two inserted residues, compared with BVMOOcean, that form a bulge near the bound flavin adenine dinucleotide in the active site. Furthermore, this bulge is linked to a nearby α-helix via a disulfide bond, probably restricting access of the bulky methyl group of the substrate to this bulge. Another sequence motif at the entrance of the active site (Ala-Ser in BVMOParvi and Ser-Thr in BVMOOcean) allows a large volume in BVMOParvi. These minute differences may discriminate a substrate orientation in both BVMOs from the initial substrate binding pocket to the final oxygenation site, resulting in the inserted oxygen atom being in different positions of the same substrate.

Rapid Crystallization for Efficient 2D Ruddlesden–Popper (2DRP) Perovskite Solar Cells

AbstractDue to the additional introduction of bulky organic ammonium and the competition between bulky organic ammonium and methyl ammonium in 2D Ruddlesden‐Popper (2DRP) perovskite, the crystallization process becomes complicated. Here, it is demonstrated that the rapid crystallization controlled by processing solvents plays an important role in achieving high‐quality 2DRP perovskite films. It is found that the processing solvents, e.g., dimethylacetamide (DMAC), N,N‐dimethylformamide (DMF), and dimethyl sulfoxide (DMSO), with a different polarity and boiling point, have almost no effect on crystal structure and phase distribution but have a remarkable effect on crystallization kinetics, crystal growth orientation, and crystallinity of 2DRP perovskite. Compared to polar aprotic solvent DMF and DMSO with a high boiling point, DMAC with low polarity and a suitable boiling point has a weak coordination to lead and ammonium salts and is easy to escape during solution processing, which is able to accelerate the crystallization rate of 2DRP perovskite. Benefitting from the rapid crystallization enabled high‐quality 2DRP perovskite films, the best‐performing device with improved stability and a power conversion efficiency of 12.15% is obtained using DMAC solvent. These findings may give guidance for solvent engineering for highly efficient 2DRP perovskite solar cells in the future.

Critical role of chloride in organic ammonium spacer on the performance of Low-dimensional Ruddlesden-Popper perovskite solar cells

Low-dimensional Ruddlesden-Popper (LDRP) perovskites attracted remarkable attention due to their technologically relevant intrinsic photo- and chemical-stability, suppressed ion migration, and ultralow self-doping effect over their 3D counterpart. The power conversion efficiency over 14% was recently achieved since the initial demonstration of LDRP perovskite solar cells (PSCs) in 2014. However, further improvements require a fundamental understanding on the components functionality in LDRP perovskites, e.g., bulky organic ammonium spacer and halogen ions, which are critical for designing efficient LDRP PSCs. Here, we report the critical role of the chloride that are derived from halogenated organic ammonium salts on the LDRP perovskite film crystallization, growth, opto-electric properties, and device performance. We found that the expected improvements in perovskite morphology with increased grain size, enhanced crystallinity, and uniform and smooth surface were revealed no matter which introduced chloride either by bulky organic ammonium or methyl ammonium salts. We also unambiguously demonstrated that photocurrent and photovoltage of LDRP PSCs are highly related to the position of chloride on organic ammonium salts. Moreover, the films and devices maintain excellent stability by the introduction of chloride due to the excellent film quality. The resulting LDRP PSCs exhibited best efficiency of 12.78%, which is two times enhancement compared to all iodide-contained device (6.52%) commonly used in previous reports. These findings demonstrated that chloride plays a significant role in LDRP perovskite and detected a key parameter for the development of future LDRP perovskite absorbers and relevant optoelectronic devices.

Solution-processable methyl-substituted semi-alicyclic homo- and co-polyimides and their gas permeation properties

Because of their excellent thermal, chemical and physical properties, as well as high gas selectivity, polyimides are promising polymers for gas separation membranes. However, their commercial use is limited due to their relatively poor solubility and permeability. Here, 5-(2,5-dioxotetrahydrofuryl)-3-methyl-cyclohexane-1,2-dicarboxylic anhydride (DOCDA) was used to improve the solubility of the polyimides, and various methyl-substituted diamines were introduced to increase their permeability, due to the effect of the bulky methyl groups. Polyimides based on DOCDA (DOCDA-PIs), synthesized via one-step solution polymerization, exhibited high solubility in common organic solvents and improved gas permeability due to the non-planar structure of DOCDA and the presence of methyl groups, which disturbed chain packing, an effect that was correlated with increased fractional free volume (FFV) and d-spacing. Co-polyimides based on DOCDA, DOCDA-coPIs, exhibited high gas permeability and CO2/CH4 and O2/N2 selectivity, comparable to commercial polymeric membranes.

Steric-Induced Fluorescence via Methyl Substitution in Chalcone Dyes

Chemical research of luminescent dyes can have potential benefits in cell microscopy, optoelectronics and textiles. Luminescent chalcones have been studied extensively for their florescence properties and sensing capabilities, such as halochromism (pH), solvatochromism (polarity), and viscochromism (viscosity). Properties such as viscochromism can be utilized to sense the membrane viscosity in cells. To probe the viscochromic behavior of chalcones, bulky methyl-substituents were incorporated into the design of the chalcone to probe planarity, brightness and fluorescence turn-on based of environmental viscosity. This was achieved via Aldol condensation of aromatic ketones and para-(dimethylamino) benzaldehyde to incorporate a bulky methyl groups at an aromatic or vinyl positions. Synthesis of the derivatives was confirmed by 1H NMR, TLC and IR spectroscopy. Preliminary results indicate the dyes have yellow-green florescence in dichromomethane (Q.Y. ~12%), and aggregation induced emission (AIE) properties. This presentation will discuss the optical properties in solution, future directions and possible applications.

Effect of Structure of Polymeric Nickel Complexes with Salen-Type Ligands on the Rate of Their Electroactivity Decay in Solutions of Water-Containing Electrolytes

The influence of the structure of diimine bridge in the Schiff’s bases (derivatives of N,N'-ethylenebissalicylimine) on the rate of the loss of electroactivity of their complexes with nickel in acetonitrile containing 0.1 M of tetraethylammonium tetrafluoroborate (anhydrous and upon addition of 1 wt % of water) has been studied. It has been shown that the presence of bulky yet light methyl groups in the structure of diimine bridge significantly reduced the loss of electroactivity (37% of the initial capacity retained after 50 cycles) as compared to the ligand containing no substituents and containing phenyl group as the substituent (17 and 20%, respectively, of initial capacity retained after 50 cycles).

Probing the effects of steric bulk on the solution-phase behaviour and redox chemistry of cobalt-diimine complexes

Cobalt-diimine complexes are important structural and redox-active elements in supramolecular assemblies. However, functionalisation of the diimine ligand adjacent to the N-donor atoms can affect dramatically the types of Co-diimine complexes that can form and their redox activity. Herein, we compare the solution phase and redox chemistry of Co(II) complexes with 1,10-phenanthroline, 5,5′-dimethyl-2,2′-bipyridine and 2,9-dimethyl-1,10-phenanthroline (neocuproine). In acetonitrile solutions containing Co(NO3)2 and neocuproine, the dominant species is the mono-diimine complex [Co(neocuproine)(NO3)(CH3CN)2]+. This complex cannot be oxidised, either electrochemically nor with iodine. We rationalise this behaviour by considering the steric constraints placed upon the metal centre by the bulky methyl substituents on the neocuproine ligand. Furthermore, from solutions of [Co(neocuproine)(NO3)(CH3CN)2]+, crystals of formula [Co(neocuproine)2(NO3)]+·[Co(neocuproine)(NO3)3]− can be obtained. We believe that this work will guide the development of Co-diimine supramolecular assemblies by highlighting the extent to which substituents close to the N-donor atoms affect which species form in solution, and their likely redox activity.