Processing-Dependent Lamellar Polymorphism of Hyperbranched Liquid-Crystalline Polymer with Variable Light Emission

Abstract

Controlling polymorphism in ordered molecular solids through manipulation of processing method has been rarely addressed despite its significance in creating assembled molecular materials with desired functions. We here report a hyperbranched liquid-crystalline polymer that showed variable lamellar smectic phases, depending on the processing methods by regulation of the kinetics involved assembly process to control the molecular packing arrangement in different lamellar arrays. The processing-dependent polymorphism enabled multicolored light emission of the liquid-crystalline polymer including cyan, green, and yellow light, showing variant degree of bathochromic shift with respect to the blue fluorescence in highly dilute solution. With a good correlation between the processing methods, hierarchically assembled structures, and light emission properties of the hyperbranched liquid crystalline polymer, it would have broad implications in pathwaydependent supramolecular self-assembly and provide a guidance for the development of adaptive functional materials in different situations.

Perylene Bisimide-Based Luminescent Liquid Crystals with Tunable Solid-State Light Emission

“…The absorption spectrum in the solid state became broader and less structured, and the absorption maximum was around 505 nm, showing a hypsochromatic shift of about 18 nm with respect to that in the diluted solution. These spectrum features suggested the H-type aggregate behavior in the LC state by referring to the interpretation for similar spectra observed for PBI chromophores in organic solvents. ,, In comparison to the well-resolved emission spectrum in solution, the solid-state fluorescence exhibited a broad emission band between 530 and 850 nm, showing a significant bathochromic shift resulting from the electronic coupling between PBI chromophores in the ordered LC state (Figure b). − The solid-state maximum emission was nearly 647 nm with a relatively high Φ F of 10%. This emission is in the deep-red region, which has rarely been reported in LC materials and is highly desirable for many advanced applications. , This result seems to contrast the common perception that the fluorescence of H-aggregates is strongly quenched; however, such strong fluorescence in H-type aggregation has also been reported in some cases. − The unexpected fluorescence in H-aggregates is accounted for the excimer species or due to a slight rotation of the two coupled molecules in the excited state. , …”

“…The MPBI compound was synthesized by using known procedures from the commercially available perylene-3,4,9,10-tetracarboxylicdianhydride . The TCS compound was designed and prepared according to our experience on the cyanostilbene-based LC compounds and polymers, − and the obtained compound was confirmed by 1 H and 13 C nuclear magnetic resonance (NMR) spectroscopy, mass spectrometry, and elemental analysis. Note that the as-prepared TCS compound was identified to adopt a thermodynamically stable all-trans Z , Z , Z -TCS form and can transform into another Z , Z , E -TCS isomer (Figure b) as discussed in detail later.…”

Positional Isomerism-Mediated Copolymerization Realizing the Continuous Luminescence Color-Tuning of Liquid-Crystalline Polymers

“…As expected, 1 H and 13 C nuclear magnetic resonance, mass spectrometry, and rotational frame nuclear Overhauser effect spectroscopy experiments (Figures S29–S32) unambiguously confirmed the occurrence of photoinduced [2 + 2] cycloaddition into the anti head-to-head cyclobutane (Figure c). In contrast to photoinduced trans – cis isomerization for CS-containing polymers, ,, [2 + 2] cycloaddition has often been observed in the bulk state. ,,, The ordered packing ability of the CS moieties possibly accounted for the strong tendency for the occurrence of [2 + 2] cycloaddition instead of trans – cis isomerization. It was also interesting that photostimulation with a different wavelength could reverse the [2 + 2] cycloaddition process for the polymers.…”

“…Light-emitting liquid crystals have recently attracted considerable interest because of the advantageous combination of unique anisotropic self-organization properties − and solid-state light emissions, − which have shown great potential for applications in a variety of fields, including polarized light emissions, information storage, multichromic fluorescence sensors, and particularly emissive liquid crystal displays. − For both basic research and practical use, it is of great interest to construct multicolor light-emitting liquid-crystalline (LC) materials for which the emission color can be precisely engineered in a simple manner. − However, the color-tuning in liquid crystals primarily depends on the derivatization of mesogenic fluorophores, − which usually limits the diversity of the emission and is largely restricted to the static fluorescence switching between several specific colors. Besides, the emission color may be changed by external stimulation upon regulating the molecular conformation or packing structure, − but the strong dependence of fluorescence output on the aggregation structure usually causes unpredictable properties in the emissions. Therefore, it is of great interest but remains challenging to develop a versatile strategy to obtain multicolor light-emitting LC materials that can be fine-tuned regarding their emission colors.…”

Functional Hyperbranched Polythioamides Synthesized from Catalyst‐free Multicomponent Polymerization of Elemental Sulfur†

“…Hyperbranched polymers with unique three dimensional topological structures, large number of branching sites and terminal groups, generally show different solubility, [ 1 ] viscosity, [ 2 ] mechanical properties, [ 3 ] ionic conductivity, [ 4‐5 ] and self‐assembly properties, [ 6 ] compared with the corresponding linear polymers, and are of great potential in the applications such as coating, [ 7‐8 ] lubricating, [ 9 ] light‐harvesting, [ 10 ] drug sustained release agents and membranes, [ 11‐14 ] polyelectrolytes, [ 4‐5 ] and luminescent materials. [ 6,15‐18 ] On the other hand, sulfur‐containing polymers including polythioethers, [ 19‐20 ] polythioesters, [ 21‐22 ] poly(monothiocarbonate)s, [ 23 ] polytrithiocarbonates, [ 24 ] polythioureas, [ 25 ] polythioamides, [ 26 ] polythiophenes, [ 27 ] and others, which generally enjoy high refractive indices, [ 28 ] excellent metal coordination ability, [ 25,29‐30 ] self‐repairing performance, [ 31 ] electrical conductivity, [ 27,32‐33 ] and degradability, [ 34‐36 ] have attracted much attention as advanced materials in the applications including optical materials, [ 37 ] sewage treatment materials, [ 30,38 ] self‐healing materials [ 31 ] and dielectric materials. [ 32,33 ] However, limited examples about sulfur‐containing hyperbranched polymers such as disulfide‐containing hyperbranched poly(amido amine)s with controllable bioreducibility and stimuli‐responsive property were developed, [ 39‐44 ] due to the lack of efficient synthetic approaches, and current methods generally involve sulfur‐bearing smelly and toxic monomers or byproducts.…”