Stability of the A15 phase in diblock copolymer melts Bates, Morgan W.; Lequieu, Joshua; Barbon, Stephanie M. ...
Proceedings of the National Academy of Sciences - PNAS,
07/2019, Letnik:
116, Številka:
27
Journal Article
Recenzirano
Odprti dostop
The self-assembly of block polymers into well-ordered nanostructures underpins their utility across fundamental and applied polymer science, yet only a handful of equilibrium morphologies are known ...with the simplest AB-type materials. Here, we report the discovery of the A15 sphere phase in single-component diblock copolymer melts comprising poly(dodecyl acrylate)−block−poly(lactide). A systematic exploration of phase space revealed that A15 forms across a substantial range of minority lactide block volume fractions (f
L = 0.25 − 0.33) situated between the σ-sphere phase and hexagonally close-packed cylinders. Self-consistent field theory rationalizes the thermodynamic stability of A15 as a consequence of extreme conformational asymmetry. The experimentally observed A15−disorder phase transition is not captured using mean-field approximations but instead arises due to composition fluctuations as evidenced by fully fluctuating field-theoretic simulations. This combination of experiments and field-theoretic simulations provides rational design rules that can be used to generate unique, polymer-based mesophases through self-assembly.
Five new compounds comprised of unprecedented boron–nitrogen heterocycles have been isolated from a single reaction of a potentially tetradentate N2O23− formazanate ligand with BF3⋅OEt2 and NEt3. ...Optimized yields for each product were obtained through variation of experimental conditions and rationalized in terms of relative Gibbs free energies of the products as determined by electronic structure calculations. Chemical reduction of two of these compounds resulted in the formation of a stable anion, radical anion, and diradical dianion. Structural and electronic properties of this new family of redox‐active heterocycles were characterized using UV/vis absorption spectroscopy, cyclic voltammetry and X‐ray crystallography.
Nice surprise: Five novel boron‐nitrogen heterocycles based on an N2O23− formazanate ligand have been isolated as unexpected products of a single reaction. The reduction of two of these heterocycles yielded an unusual anion, radical anion, and diradical dianion.
Electrochemiluminescence (ECL) of a boron difluoride formazanate dye was investigated in the presence of tri-n-propylamine as a reductive co-reactant. The ECL mechanism was studied using ECL-voltage ...curves, spooling ECL, and accumulative ECL spectroscopy. The ECL occurs at 724 nm by three distinct, voltage-dependent mechanisms of light emission.
Evaluation of three subclasses of boron difluoride formazanate complexes bearing o‐, m‐, and p‐anisole N‐aryl substituents (Ar) as readily accessible alternatives to boron dipyrromethene (BODIPY) ...dyes for cell imaging applications is described. While the wavelengths of maximum absorption (λmax) and emission (λem) observed for each subclass of complexes, which differed by their carbon‐bound substituents (R), were similar, the emission quantum yields for 7 a–c (R=cyano) were enhanced relative to 8 a–c (R=nitro) and 9 a–c (R=phenyl). Complexes 7 a–c and 8 a–c were also significantly easier to reduce electrochemically to their radical anion and dianion forms compared to 9 a–c. Within each subclass, the o‐substituted derivatives were more difficult to reduce, had shorter λmax and λem, and lower emission quantum yields than the p‐substituted analogues as a result of sterically driven twisting of the N‐aryl substituents and a decrease in the degree of π‐conjugation. The m‐substituted complexes were the least difficult to reduce and possessed intermediate λmax, λem, and quantum yields. The complexes studied also exhibited large Stokes shifts (82–152 nm, 2143–5483 cm−1). Finally, the utility of complex 7 c (Ar=p‐anisole, R=cyano), which can be prepared for just a few dollars per gram, for fluorescence cell imaging was demonstrated. The use of 7 c and 4′,6‐diamino‐2‐phenylindole (DAPI) allowed for simultaneous imaging of the cytoplasm and nucleus of mouse fibroblast cells.
Evaluation of nine boron difluoride formazanate complexes bearing o‐, m‐, and p‐anisole N‐aryl substituents as readily accessible alternatives to boron dipyrromethene (BODIPY) dyes for cell‐imaging applications is presented. Highlights include the demonstration of the dramatic effect of anisole substitution patterns on the properties of the resulting complexes and the utility of a champion complex for fluorescence cell imaging of the cytoplasm of mouse fibroblast cells.
The synthesis and characterization of a flexidentate pyridine-substituted formazanate ligand and its boron difluoride adducts, formed via two different coordination modes of the title ligand, are ...described. The first adduct adopted a structure that was typical of other boron difluoride adducts of triarylformazanate ligands and contained a free pyridine subsituent, while the second was formed via the chelation of nitrogen atoms from the formazanate backbone and the pyridine substituent. Stepwise protonation of the pydridine-functionalized adduct, which is essentially nonemissive, resulted in a significant increase in the fluorescence quantum yield up to a maximum of 18%, prompting the study of this adduct as a pH sensor. The coordination chemistry of each adduct was explored through reactions with nickel(II) bromide NiBr2(CH3CN)2, triflate Ni(OTf)2, and 1,1,1,4,4,4-hexafluoroacetylacetonate Ni(hfac)2(H2O)2 salts. Coordination to nickel(II) ions altered the physical properties of the boron difluoride formazanate adducts, including red-shifted absorption maxima and less negative reduction potentials. Together, these studies have demonstrated that the physical and electronic properties of boron difluoride adducts of formazanate ligands can be readily modulated through protonation and coordination chemistry.
A versatile and scalable strategy is reported for the rapid generation of block copolymer libraries spanning a wide range of compositions starting from a single parent copolymer. This strategy ...employs automated and operationally simple chromatographic separation that is demonstrated to be applicable to a variety of block copolymer chemistries on multigram scales with excellent mass recovery. The corresponding phase diagrams exhibit increased compositional resolution compared to those traditionally constructed via multiple, individual block copolymer syntheses. Increased uniformity and lower dispersity of the chromatographic libraries lead to differences in the location of order–order transitions and observable morphologies, highlighting the influence of dispersity on the self-assembly of block copolymers. Significantly, this separation technique greatly simplifies the exploration of block copolymer phase space across a range of compositions, monomer pairs, and molecular weights (up to 50000 amu), producing materials with increased control and homogeneity when compared to conventional strategies.
The hexagonally close-packed (HCP) sphere phase is predicted to be stable across a narrow region of linear block copolymer phase space, but the small free energy difference separating it from ...face-centered cubic spheres usually results in phase coexistence. Here, we report the discovery of pure HCP spheres in linear block copolymer melts with A = poly(2,2,2-trifluoroethyl acrylate) (“F”) and B = poly(2-dodecyl acrylate) (“2D”) or poly(4-dodecyl acrylate) (“4D”). In 4DF diblocks and F4DF triblocks, the HCP phase emerges across a substantial range of A-block volume fractions (circa f A = 0.25–0.30), and in F4DF, it forms reversibly when subjected to various processing conditions which suggests an equilibrium state. The time scale associated with forming pure HCP upon quenching from a disordered liquid is intermediate to the ordering kinetics of the Frank–Kasper σ and A15 phases. However, unlike σ and A15, HCP nucleates directly from a supercooled liquid or soft solid without proceeding through an intermediate quasicrystal. Self-consistent field theory calculations indicate the stability of HCP is intimately tied to small amounts of molar mass dispersity (Đ); for example, an HCP-forming F4DF sample with f A = 0.27 has an experimentally measured Đ = 1.04. These insights challenge the conventional wisdom that pure HCP is difficult to access in linear block copolymer melts without the use of blending or other complex processing techniques.
The straightforward synthesis of a series of 3‐cyanoformazanate boron difluoride dyes is reported. Phenyl, 4‐methoxyphenyl and 4‐cyanophenyl N‐substituted derivatives were isolated and characterized ...by single‐crystal X‐ray crystallography, cyclic voltammetry, and UV/Vis spectroscopy. The compounds were demonstrated to possess tunable, substituent‐dependent absorption, emission, and electrochemical properties, which were rationalized through electronic structure calculations.
Simple but bright: A novel class of boron difluoride dyes based on 3‐cyanoformazanate ligands is reported. The dyes were synthesized by straightforward synthetic methods and shown to possess readily tunable and substituent‐dependent absorption, emission, and electrochemical properties. The trends observed in experimental results were confirmed and rationalized by using electronic structure calculations.
The straightforward synthesis and detailed characterization of nine substituted triarylformazanate boron difluoride complexes is reported. The effect of electron-donating (p-anisole) and ...electron-withdrawing (p-benzonitrile) substituents on optical and electrochemical properties, relative to phenyl substituents, was studied at two different positions within the formazanate ligand framework. Each of the BF2 complexes was characterized by 1H, 13C, 11B, and 19F NMR spectroscopy, cyclic voltammetry, infrared spectroscopy, UV–vis absorption and emission spectroscopy, mass spectrometry, and elemental analysis. Select examples were studied by X-ray crystallography, revealing highly delocalized structures in the solid state. The complexes were reversibly reduced in two steps electrochemically to their radical anion and dianion forms. The complexes also exhibited substituent-dependent absorption and emission properties, accompanied by significant Stokes shifts, with the aryl substituents at the 1,5-positions of the formazanate backbone having a greater influence on these properties than aryl substituents at the 3-position. Breaking the symmetry in three different complexes resulted in a modest increase in emission intensity relative to that of symmetrically substituted derivatives.
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