LCDiXRay: a user-friendly program for powder diffraction indexing of columnar liquid crystals

Photoactivable malachite green-based alkynylplatinum(II) 2,6-bis(N-alkylbenzimidazol-2-yl)pyridine complexes

Photo-responsive malachite green moieties have been incorporated into an alkynylplatinum(II) bzimpy system. The photo-caged complexes in acetonitrile solutions exhibit self-assembly properties modulable by photo-removal of the cyano protecting group. Distinct aggregate morphologies, which are facilitated by the non-covalent metal-metal and π-π stacking interactions, have been observed before and after photo-irradiation.

A novel B,O,N-doped mesogen with narrowband MR-TADF emission

Modification of an unsymmetric B,O,N-doped aromatic core with peripheral mesogenic units triggers self-assembly into a columnar hexagonal mesophase, which is stable between 22 and 144 °C. The columnar assembly is preserved in a glassy state below 22 °C. The B,O,N-doped mesogen displays narrowband sky-blue multiresonance thermally activated delayed fluorescence (MR-TADF) under diluted conditions and bright excimer emission in condensed phase. Our combined experimental and theoretical approach provides insight into the development of strongly aggregating liquid crystalline MR-TADF emitters.

Self-Assembly of Atomically Precise Silver Nanoclusters in Crowded Colloids into Ultra-Long Ribbons with Tunable Supramolecular Chirality

Atomically precise metal nanoclusters (NCs) emerge as fascinating synthons in self-assembled materials. The self-assembly of metal NCs are highly sensitive to the environment because they have an inorganic-organic hybridized structure and a relatively complicated conformation. Here, it is shown that when confined in crowded colloids, a water-soluble Ag9 -cored nanocluster (Ag9 -NC) can self- assemble into ultra-long (up to millimeters) and photoluminescent ribbons with high flexibility. The ribbon contains rectangularly organized columns of Ag9 -NCs and can undergo secondary self-assembly to form bundled and branched structures. Formation of ribbons is observed in all the tested colloids, including lyotropic liquid crystals and disordered, three-dimensional network. The high viscosity/elasticity of the crowded colloids weakens gravity-induced sedimentation of the ribbons, leading to the formation of an interesting class of inorganic-organic composite materials where the hard Ag-containing skeleton strengthens the soft matter. The simultaneously occurring symmetry breaking during the self-assembly of Ag9 -NCs gives uncontrolled supramolecular chirality, which can be tuned through the majority rule and soldier-and-sergeant rule by the introduction of chiral seeds. The regulated chirality and the intrinsic photoluminescence of the Ag9 -NCs ribbons impart the composite material circularly polarized luminescence, opening the door for a variety of potential applications.

Two-Dimensional Supramolecular Polymerization of a Bis-Urea Macrocycle into a Brick-Like Hydrogen-Bonded Network

We report on a dendronized bis-urea macrocycle 1 self-assembling via a cooperative mechanism into two-dimensional (2D) nanosheets formed solely by alternated urea-urea hydrogen bonding interactions. The pure macrocycle self-assembles in bulk into one-dimensional liquid-crystalline columnar phases. In contrast, its self-assembly mode drastically changes in CHCl3 or tetrachloroethane, leading to 2D hydrogen-bonded networks. Theoretical calculations, complemented by previously reported crystalline structures, indicate that the 2D assembly is formed by a brick-like hydrogen bonding pattern between bis-urea macrocycles. This assembly is promoted by the swelling of the trisdodecyloxyphenyl groups upon solvation, which frustrates, due to steric effects, the formation of the thermodynamically more stable columnar macrocycle stacks. This work proposes a new design strategy to access 2D supramolecular polymers by means of a single non-covalent interaction motif, which is of great interest for materials development.

Shedding Light on Highly Emissive 1,4-Dihydropyrrolo[3,2-b]pyrrole Derivatives: Synthesis and Aggregate-Dependent Emission

Three tetraaryl-1,4-dihydropyrrolo[3,2-b]pyrrole derivatives containing different number of long alkoxy chains (2, 4 and 6) were synthesized, characterized and applied in Organic Light Emitting Diodes (OLEDs). The compounds showed good emission properties with Photoluminescence Quantum Yields (PLQYs) higher than 80 % in solution and 50 % in solid state (thin film). The solvatochromism results revealed a pronounced vibronic emission in methylcyclohexane and toluene, characterized by two distinct sharp emission peaks and a small redshift in the following order: methylcyclohexane>toluene>dichloromethane>tetrahydrofuran>acetonitrile. Also, the compounds formed aggregates with redshifted emission, which can be attributed to excimer formation. This phenomenon was observed in solutions containing 90 % water and with the concentration variation in methylcyclohexane (MCH). Compounds with a greater number of peripheral chains showed the capacity to keep hexagonal columnar organization in films after fast cooling from liquid state. OLEDs fabricated with these compounds showed turn-on voltages lower than 4.0 V, with luminance higher than 1400 cd m-2 , electroluminescence spectra with Full Width at Half Maximum lower than 70 nm and maximum External Quantum Efficiency between 7.2 % and 4.3 %. Overall, this shows that the 1,4-dihydropyrrolo[3,2-b]pyrrole moiety is promising for applications where luminescence is paramount, as in organic light-emitting devices.

Benzopyrano-Fused Phenanthridine-Based Columnar Mesogens: Synthesis, Self-organization and Charge-Transport Properties

Columnar mesogens constitute a fascinating class of supramolecular nano-architectures owing to the exceptional properties induced by their self-assembling behavior. Extending the π-conjugated core in such systems by incorporating heteroatoms extensively influences their mesomorphic, photophysical properties, etc., presenting them as potential candidates for optoelectronic applications. In the present work, a series of novel nitrogen and oxygen-incorporated chromenonaphthophenanthridine-based elliptical dimers have been synthesized through tandem Pictet-Spengler cyclization followed by ipso-aromatic substitution in one-pot. Mesophase characterization has been carried out by employing POM, DSC, and X-ray diffraction studies. Photophysical properties were investigated using UV-vis and emission spectroscopy. Furthermore, the charge transport properties were analyzed by time-of-flight measurements, and the observed ambipolar mobilities were found to be of the order of 10^-3  cm²  V^-1  s^-1 . The high solubility, excellent thermal stability, self-organizing properties, and ambipolar charge transport characteristics make them promising candidates for applications in organic electronics.

Motoc) S, Visan A, Cretu C, Scarpelli F, Crispini A, Manea F, Szerb EI. Hetero-Bimetallic Ferrocene-Containing Zinc(II)-Terpyridyl-Based Metallomesogen: Structural and Electrochemical Characterization

The synthesis, as well as the mesomorphic and electrochemical properties, of a hetero-bimetallic coordination complex able to self-assemble into a columnar liquid crystalline phase is reported herein. The mesomorphic properties were investigated by polarized optical microscopy (POM), differential scanning calorimetry (DSC) and Powder X-ray diffraction (PXRD) analysis. Electrochemical properties were explored by cyclic voltammetry (CV), relating the hetero-bimetallic complex behaviour to previously reported analogous monometallic Zn(II) compounds. The obtained results highlight how the presence of the second metal centre and the supramolecular arrangement in the condensed state pilot the function and properties of the new hetero-bimetallic Zn/Fe coordination complex.

Self-Assembly of Alkylamido Isophthalic Acids toward the Design of a Supergelator: Phase-Selective Gelation and Dye Adsorption

A new series of 5-alkylamido isophthalic acid (ISA) derivatives with varying single and twin alkyl chain lengths were designed and synthesized as potential supramolecular organogelators. 5-alkylamido ISAs with linear or branched alkyl tail-groups of different lengths were effective gelators for low polarity solvents. In particular, among the presented series, a derivative with a branched, 24 carbon atom tail-group behaves as a “supergelator” with up to twenty organic solvents forming gels that are highly stable over time. The gelation behavior was analyzed using Hansen solubility parameters, and the thermal stability and viscoelastic properties of select gels were characterized. Microscopy, spectroscopy, powder X-ray diffraction, and computer modeling studies were consistent with a hierarchical self-assembly process involving the formation of cyclic H-bonded hexamers via the ISA carboxylic acid groups, which stack into elementary fibers stabilized by H-bonding of the amide linker groups and π–π stacking of the aromatic groups. These new nanomaterials exhibited potential for the phase-selective gelation of oil from oil–water mixtures and dye uptake from contaminated water. The work expands upon the design and synthesis of supramolecular self-assembled nanomaterials and their application in water purification/remediation.

Strikingly different molecular organization and molecular order of tetracatenar mesogens in columnar mesophases revealed by XRD and 13C NMR

For a successful design of functional mesogens, it is paramount to understand factors that contribute to molecular organisation such as molecular shape, the non-covalent interactions of the constituent moieties as well as nanosegregation of incompatible molecular parts. In this study on four tetracatenar mesogens, we show that by a slight change in the length of the terminal chain, the molecular organization changes from lamellar to columnar phase and that the orientational order experiences profound change between the lamellar, the center rectangular columnar and the hexagonal columnar mesophases. We consider here, mesogens that exhibit lamellar and columnar mesophases with five phenyl rings in the central rod-like core which are subjected to XRD and high resolution solid state ¹³C NMR investigations in their mesophases. The XRD studies indicate that the lower homologs exhibit a lamellar mesophase while the higher homologs show either a centre rectangular columnar phase or a 2D hexagonal columnar mesophase. ¹³C NMR investigations reveal interesting and strikingly different molecular orientations in each of these phases. For example, values of order parameters of one of the phenyl rings in the core region of the mesogens vary from 0.75 and 0.77 for the lamellar mesogens to 0.45 and 0.17 for the centre rectangular columnar and the hexagonal columnar mesogens respectively. While these values indicate that the mesogenic molecules are oriented along the magnetic field as expected in the lamellar phases, the very low order parameter in the hexagonal columnar phase arises due to molecules distributed azimuthally in layers and undergoing motion about the columnar axis which itself is oriented orthogonal to the magnetic field. Such cutting edge information extracted from the combined use of XRD and ¹³C NMR studies on tetracatenar mesogens is expected to be of significant use for the study of π-conjugated polycatenar systems where functional properties depend on the molecular orientation and order.

Preparation and Characterization of Silver(I) Ethylcellulose Thin Films as Potential Food Packaging Materials

Ag(I)-containing ethylcellulose (EC) films suitable as antbacterial packaging materials have been prepared and fully characterized. Different preparation methods, including the use of green casting solvents, are proposed. The Ag(I) acylpyrazolonato complexes, [Ag(Q^py,CF3 )(L)], L=benzylimidazole (Bzim) and L=ethylimidazole (EtimH), used as active additives, display different modes of interactions with EC, depending on their structural features. A thorough investigation of the EC liquid-crystalline lyotropic phase and its changes with the introduction of silver additives, has been conducted, revealing either the inclusion of complex molecules into the inner structure of the EC matrix or their dispersion on its surface. Moreover, the bactericidal activity of the prepared Ag(I) films seems to be related to the interaction between silver additives and the polymeric EC matrix. Indeed, the EC-2b films show a particularly good performance even with a low silver content, with a relative bacterial killing of about 100 %. Tests for Ag(I) migration have been performed by using three food stimulants under two assay conditions. Low values of silver release are recorded, particularly at low concentration of silver content, in the case of all new prepared Ag(I) films.

Ionic-surfactants-based thermotropic liquid crystals

Ionic surfactants can be combined with various functional groups through electrostatic interaction, resulting in a series of thermotropic liquid crystals (TLCs).

High Order in a Self-Assembled Iridium(III) Complex Gelator Towards Nanostructured IrO2 Thin Films

The preparation and characterization of a new metallogelator based on the Ir^III discrete cyclometalated complex [(ppy)₂ Ir(bpy)](CH₃ CH₂ OCH₂ CO₂ ) are reported, where H(ppy) is 2-phenylpiridine and bpy is 2,2'-bipyridine, which is used as an ancillary ligand. The compound is able to self-assemble in water in a range of concentrations between 3 % and 6 % w/w, creating a luminescent ordered supramolecular gel. The gel and xerogel architectures were investigated through polarized optical microscopy (POM), SEM and TEM microscopies coupled with powder X-ray diffraction. The gel supramolecular organization is characterized by columnar tetragonal strands, already present at high dilution conditions, of cations surrounded by counteranions. These strands, in turn, are self-assembled in an oblique columnar cell upon gelification. The xerogel thin films obtained upon complete dehydration maintained the gel supramolecular order and can be used as a precursor for the preparation of nanostructured IrO₂ thin films.