Photopatternable electrochromic materials from oxetane precursors

Electrochemical and Optical Properties of D-A-A-A-D Azomethine Triad and Its NIR-Active Polymer

The azomethine TPA-(BTZ)3-TPA with a donor-acceptor-acceptor-acceptor-donor structure has been synthesized and characterized. Azomethine TPA-(BTZ)3-TPA exhibited luminescence properties and a positive solvatochromic effect. Electropolymerization on terminated triphenylamine groups was used to obtain a thin layer of the polyazomethine poly-[TPA-(BTZ)3-TPA]. Further investigation of oxidation/reduction properties of poly-[TPA-(BTZ)3-TPA] via cyclic voltammetry showed that the polymer undergoes two reversible oxidation/reduction processes due to the presence of tetraphenylbenzidine moieties. Electrochromic properties of the polyazomethine poly-[TPA-(BTZ)3-TPA] were investigated via spectroelectrochemistry. It was observed that the polymer in its neutral state is orange, and the color changes to green upon electro-oxidation. The stability of the polymer during multiple oxidation/reduction cycles, response times, and coloration efficiency were also investigated.

Stereoselective Synthesis of Oxetanes Catalyzed by an Engineered Halohydrin Dehalogenase

Although biocatalysis has garnered widespread attention in both industrial and academic realms, the enzymatic synthesis of chiral oxetanes remains an underdeveloped field. Halohydrin dehalogenases (HHDHs) are industrially relevant enzymes that have been engineered to accomplish the reversible transformation of epoxides. In this study, a biocatalytic platform was constructed for the stereoselective kinetic resolution of chiral oxetanes and formation of 1,3-disubstituted alcohols. HheC from Agrobacterium radiobacter AD1 was engineered to identify key variants capable of catalyzing the dehalogenation of γ-haloalcohols (via HheC M1-M3) and ring opening of oxetanes (via HheC M4-M5) to access both (R)- and (S)-configured products with high stereoselectivity and remarkable catalytic activity, yielding up to 49 % with enantioselectivities exceeding 99 % ee and E>200. The current strategy is broadly applicable as demonstrated by expansion of the substrate scope to include up to 18 examples for dehalogenation and 16 examples for ring opening. Additionally, the functionalized products are versatile building blocks for pharmaceutical applications. To shed light on the molecular recognition mechanisms for the relevant variants, molecular dynamic (MD) simulations were performed. The current strategy expands the scope of HHDH-catalyzed chiral oxetane ring construction, offering efficient access to both enantiomers of chiral oxetanes and 1,3-disubstituted alcohols.

On-Substrate Preparation of a Poly(triphenylamino azomethine) for Electrochromic Devices

An electroactive polyazomethine was prepared directly on a transparent electrode by the polycondensation of bis(triphenylamine) dialdehyde and its complementary methoxytriphenylamine diamine. The spray-and-bake method of coating the electrode for preparing electrochromic layers could be upscaled to prepare working devices larger than standard test devices. The film prepared by thermally annealing the complementary monomers was both electroactive and switched its color with an applied potential. The yellow electrochromic polyazomethine could be electrochemically oxidized reversibly to obtain a blue film. The electrochromic test device fabricated from the polyazomethine was operated upwards of 1 h for performance assessment. The electrochromic response times of the electrochromic device were ca. 3.3 and 1.2 s for the coloration and bleaching, respectively. The upscaled device prepared by the straightforward coating approach had consistent metrics with the small-area test device.

A Holistic Review of C = C Crosslinkable Conjugated Molecules in Solution-Processed Organic Electronics: Insights into Stability, Processibility, and Mechanical Properties

Solution-processable organic conjugated molecules (OCMs) consist of a series of aromatic units linked by σ-bonds, which present a relatively freedom intramolecular motion and intermolecular re-arrangement under external stimulation. The cross-linked strategy provides an effective platform to obtain OCMs network, which allows for outstanding optoelectronic, excellent physicochemical properties, and substantial improvement in device fabrication. An unsaturated double carbon-carbon bond (C = C) is universal segment to construct crosslinkable OCMs. In this review, the authors will set C = C cross-linkable units as an example to summarize the development of cross-linkable OCMs for solution-processable optoelectronic applications. First, this review provides a comprehensive overview of the distinctive chemical, physical, and optoelectronic properties arising from the cross-linking strategies employed in OCMs. Second, the methods for probing the C = C cross-linking reaction are also emphasized based on the perturbations of chemical structure and physicochemical property. Third, a series of model C = C cross-linkable units, including styrene, trifluoroethylene, and unsaturated acid ester, are further discussed to design and prepare novel OCMs. Furthermore, a concise overview of the optoelectronic applications associated with this approach is presented, including light-emitting diodes (LEDs), solar cells (SCs), and field-effect transistors (FETs). Lastly, the authors offer a concluding perspective and outlook for the improvement of OCMs and their optoelectronic application via the cross-linking strategy.

End-group functionalization of a conjugated azomethine with ureas for property tailoring

A conjugated azomethine end-capped with phenyl-ureas was prepared by a convergent approach. Hydrogen bonding with the ureas was confirmed and the spectroscopic properties could be enhanced with the supramolecular bonds.

User-Customized, Multicolor, Transparent Electrochemical Displays Based on Oxidatively Tuned Electrochromic Ion Gels

Transparent displays have emerged as a class of cutting-edge electronics. Here, we propose user-customized, design-it-yourself (DIY) transparent displays based on electrochromic (EC) ion gels including viologens. To achieve multiple colors and enhance the functionality of EC displays (ECDs), the incorporation of several EC chromophores is inevitable. However, the issue related to the discrepancy of coloration voltages is inherent due to the different electrochemical characteristics of each material, causing unbalance of the color contrast. To overcome this problem without significantly affecting the performance of ECDs, we suggest a simple but effective strategy by adjusting the oxidation activity of electrolyte-soluble anodic species (i.e., ferrocene (Fc) derivatives) by modifying pendant groups. We systematically investigated the effects of the employed Fc derivatives on the EC behaviors of ECDs in terms of the coloration voltage, maximum transmittance contrast, device dynamics, coloration efficiency, and operational stability. We determine the conditions for implementing red-green-blue (RGB) colors with comparable intensities at similar voltages. Last, we draw images using RGB EC inks for conceptual demonstration of the DIY transparent displays. The fabricated ECDs exhibit transparent bleached states and user-customized images in the colored states. Overall, this result implies that the extremely simple DIY ECDs, which do not require conventional lithography or printing, have great potential as future transparent displays that can be easily customized.

Frequency-Selective Photobleaching as a Route to Chromatic Control in Supramolecular OLED Devices

We report a series of molecules that spontaneously self-organize into small electroluminescent domains of sub-micrometer dimensions when dissolved in tetrahydrofuran. The self-assembled spherical aggregates have an average diameter of 300 nm and exhibit efficient energy transfer from the blue to the green or red component. The aggregates can be chromatically addressed or patterned by selective bleaching of the energy-acceptor component using a laser source. This allows the fabrication of electroluminescence devices by directly photopatterning the active layer without the need of additional steps. Submicron features (700 nm) can be achieved using a collimated light source.

Enhancing the electrochromic performance of conjugated polymers using thermal nanoimprint lithography

Thermal nanoimprinting is employed to create nanopatterned electrochromic conjugated polymer films, giving superior color-changing properties compared to a reference device.

Ambipolar azomethines as potential cathodic color switching materials

The electrochemical oxidation and reduction reversibility along with the electrochemically mediated color change of triad azomethines were contingent on the central aromatic.

Hydrogen-Bond and Supramolecular-Contact Mediated Fluorescence Enhancement of Electrochromic Azomethines

An electronic push-pull fluorophore consisting of an intrinsically fluorescent central fluorene capped with two diaminophenyl groups was prepared. An aminothiophene was conjugated to the two flanking diphenylamines through a fluorescent quenching azomethine bond. X-ray crystallographic analysis confirmed that the fluorophore formed multiple intermolecular supramolecular bonds. It formed two hydrogen bonds involving a terminal amine, resulting in an antiparallel supramolecular dimer. Hydrogen bonding was also confirmed by FTIR and NMR spectroscopic analyses, and further validated theoretically by DFT calculations. Intrinsic fluorescence quenching modes could be reduced by intermolecular supramolecular contacts. These contacts could be engaged at high concentrations and in thin films, resulting in fluorescence enhancement. The fluorescence of the fluorophore could also be restored to an intensity similar to its azomethine-free counterpart with the addition of water in >50 % v/v in tetrahydrofuran (THF), dimethyl sulfoxide (DMSO), and acetonitrile. The fluorophore also exhibited reversible oxidation and its color could be switched between yellow and blue when oxidized. Reversible electrochemically mediated fluorescence turn-off on turn-on was also possible.

Cross-Linkable Fluorene-Diphenylamine Derivatives for Electrochromic Applications

Multicolor electrochromic systems based on heat cross-linkable arylamine-substituted fluorene derivatives, FD and FDOMe, are reported. These derivatives with pendant vinyl groups have been synthesized by the Buchwald-Hartwig amination reaction and were well-characterized using various analytical and spectroscopic techniques such as NMR, ESI-MS, and single-crystal X-ray diffraction analysis. FD and FDOMe exhibited thermally activated cross-linking above their melting temperatures, which was confirmed through absorption, differential scanning calorimetry (DSC), FT-IR, and wide-angle X-ray diffraction (WAXD) techniques. Cross-linked FD films (FD-X) on ITO showed two reversible redox peaks at 0.74 and 0.91 V (versus Ag/AgCl) that correspond to the formation of radical cations and dications, respectively. The corresponding redox peaks were observed at 0.6 and 0.8 V for cross-linked FDOMe films (FDOMe-X). Spectroelectrochemical studies of the electrochromic films on ITO revealed multicolor electrochromism of FD-X (colorless-yellow-dark cyan) and FDOMe-X (colorless-brick red-blue) with a color contrast of ∼44% at 485 nm for FD-X and ∼63% at 500 nm for FDOMe-X and good switching stability between the neutral and oxidized states (>300 cycles) with low switching voltages (<0.9 V for the first oxidation and <1.3 V for the second oxidation). Furthermore, fabrication of electrochromic devices using FD-X and FDOMe-X on FTO substrate with PMMA-based solid electrolyte was demonstrated, where the devices exhibited reasonably low switching time between the redox states (<30 s) with good optical contrast.