Solution Synthesis Research Articles

Towards the Tetrabenzo-Fused Circumazulene via In-Solution and On-Surface Synthesis

The synthesis of circumazulene, a nonalternant isomer of circumnaphthalene, and its π-expanded derivatives poses a considerable challenge due to the lack of a suitable synthetic strategy. In this work, we present our efforts toward achieving tetrabenzo-fused circumazulene (1) through both solution and on-surface syntheses. In the case of in-solution synthesis, we obtained a product (P) with the desired target mass, but the structural verification proved to be challenging owing to the presence of various structural isomers. In the on-surface synthesis approach, a series of unexpected azulene-embedded nanographenes were obtained, including a molecule with an additional pentagonal ring (U1) based on the backbone of 1. Furthermore, theoretical calculations were conducted to shed light on these unexpected structures and to investigate their aromaticity. This work opens a new avenue for the design and synthesis of novel nonalternant graphene nanostructures incorporating circumarene.

Glutathione-Capped Quaternary Ag–(In,Ga)–S Quantum Dots Obtained by Colloidal Synthesis in Aqueous Solutions

Ag–(In,Ga)–S quantum dots (QDs) were obtained by colloidal synthesis from aqueous solutions with different [In]/[Ga] precursor ratios in the presence of glutathione ligands under mild conditions. Size-selected fractions of the colloidal solutions were separated by the repeated centrifuging with addition of 2-propanol. The QD chemical composition determined by X-ray photoelectron spectroscopy is noticeably In-enriched with respect to the precursor ratio. The QD size estimated from the halfwidth of X-ray diffraction peaks for the non-fractioned colloidal solutions is about 2 nm. The synthesized QDs reveal a shift of the absorption edge and the photoluminescence (PL) peak maximum toward higher energies with decreasing the QD size. Experimentally measured Raman spectra of the Ag–(In,Ga)–S QDs are noticeably affected by size-related factors.

Dual solution synthesis of Al doped CuS thin films for optoelectronic and photovoltaic applications

Dual Solution Synthesis (DSS) was used to deposit CuS doped with Al. The Samples were subjected to annealing under varying temperatures of 319K and 373K . The thin films were firmly adherent to the substrates. The optical properties were measured using UV -1800 series double beam spectrophotometer. The transmittance is from 0.3% to 0.6% while the reflectance is between 0.176 to 0.204, as the wavelength ranges from 320nm to 1000nm; the average band gap obtained is 2.6. The thicknesses achieved are 100nm and 124 nm. Other Optical properties were determined for each sample which makes it suitable for applications in optoelectronic, solar energy conversions, solar cells, thin film absorbers, anti- reflective coating, aesthetic windows, UV filter and other uses.

Reframing water demand management: a new co-governance framework coupling supply-side and demand-side solutions toward sustainability

Abstract. Water demand management adopts economic and non-economic measures to reduce human water use. However, it is argued in this study that water use changes may cause idle water supply facilities and revenue losses, thereby challenging the sustainability of water supply systems in the context of climate change. A co-governance framework was established to inspire practical strategies of sustaining water supply systems by re-evaluating the long-term impacts of water demand changes. This framework adopts a broader view of water demand management by integrating the political, financial, and consumptive needs of the government, the market, and the users in the form of a collaborative strategy coupling both supply-side and demand-side solutions. The proposed framework was applied to the analysis of the sustainability of China's South-to-North Water Diversion Project. It is found that the South-to-North Water Diversion Project is not a simple water supply infrastructure but rather a synthesis of supply-side and demand-side water management solutions. Actively releasing water for ecological and cultural purposes is suggested in this study to maintain the socio-ecological benefits of the project in the context of human water use decline. The economic cost of the water supply could be recovered by ongoing revenues that include not only the water fees charged to users but also the benefits gained from cooperative investment in broader water-related businesses by both the state-owned water transfer company and local governments in water-receiving areas. The proposed framework and strategies are valuable for other water utilities around the world, especially those challenged by reduced water demand caused by climate change, high water prices, and economic depression.

Investigation of cerium as a surrogate for tetravalent actinides in monazite-type compounds

The incorporation of tetravalent cerium into the monazite structure via Ca(II)-coupled substitution was investigated using a solid state and a co-precipitation route for the synthesis of the La1-2xCaxCexPO4 solid solution. Based on powder XRD measurements and elemental mappings an optimised synthesis procedure was developed that averts the formation of secondary phases and allows the stabilisation of tetravalent cerium with a ratio of up to 0.21 Ce(IV)/Ce(III). In-situ HERFD-XANES measurements at the Ce L3 edge at up to 800°C were performed to study the cerium oxidation state during the phase transformation from rhabdophane to monazite, revealing an unexpected non-linear behaviour as well as a charge-directing effect of the lanthanum cation.

Highly Efficient Broadband Near‐Infrared Emission in Cr3+‐Activated Organic Hafnium Chlorine for Multi‐Optoelectronic Applications

AbstractCr3+ ions doped broadband emission near‐infrared (NIR) phosphors are pertinent to widespread emerging applications and get rapid developed. However, it remains a challenge to simultaneously achieve highly efficient and broadband near‐infrared emission in Cr3+ ions doped phosphors. Herein, the Cr3+ ions firstly doped into organic–inorganic hafnium chlorine TEA2HfCl6 (TEA = Tetraethylammonium, C8H20N), which show broadband emission at a range of 700–1300 nm, a full width at half maximum (FWHM) of 164 nm, and a high photoluminescence quantum yield (PLQY) of 60%. The organic–inorganic metal halides show huge advantages than traditional inorganic phosphors, like high luminescence efficiency, low temperature solution synthesis progress, and low cost, which provide an efficiency strategy for lighting industry. Based on these advantages, a high power NIR light emitting diode (LED) is fabricated by TEA2HfCl6:Cr3+ with a high‐power 530 nm chip, which is used in food analysis, night vision, and biomedical imaging as a demonstration. This work indicates the feasibility of organic–inorganic metal halides as host materials for developing Cr3+ ions emitting phosphor toward multi‐optoelectronic applications.

Soft yet mechanically robust injectable alginate hydrogels with processing versatility based on alginate/hydroxyapatite hybridization

The salient gelling feature of alginate via forming the egg-box structure with calcium ions has received extensive interests for different applications. Owing to the interfacial incompatibility of rigid inorganic solids with soft polymers, the requirement of overall stereocomplexation with calcium released from uniformly distributed solids in alginate remains a challenge. In this study, a novel alginate-incorporated calcium source was proposed to tackle the intractable dispersion for the preparation of injectable alginate hydrogels. Calcium phosphate synthesis in alginate solution yielded CaP-alginate hybrids as a calcium source. The physicochemical characterization confirmed the CaP-alginate hybrid was a nano-scale alginate-hydroxyapatite complex. The colloidally stable CaP-alginate hybrids were uniformly dispersed in alginate solutions even under centrifugation. The calcium-induced gelling of the CaP-alginate hybrids-loaded alginate solutions formed soft yet tough hydrogels including transparent sheets and knittable threads, confirming the homogeneous gelation of the hydrogel. The gelation time, injectability and mechanical properties of the hydrogels could be adjusted by changing preparation parameters. The prepared hydrogels showed uniform porous structure, excellent swelling, wetting properties and cytocompatibility, showing a great potential for applications in different fields. The present strategy with organic/inorganic hybridization could be exemplarily followed in the future development of functional hydrogels especially associated with the interface integration.

Micropatternable Ink Composed of MAX Phase ZIF-8 for Gas Sensing Applications

This work provides a detailed introduction to the preparation methods, structural characteristics, and various performance tests of the Ti3C2/ZIF-8 composite material. Initially, the composite material is obtained through the synthesis, mixing, and subsequent processing of MXene solution and ZIF-8 nanoparticles. The coating structure and properties were comprehensively characterized using SEM, TEM, and XRD. These analyses revealed the material's layered structure, high crystallinity, and surface activity. BET analysis of Ti3C2/ZIF-8 also shows excellent gas adsorption-desorption performance, having an especially high-efficiency adsorption capacity for VOCs. TGA further demonstrates the thermal stability and chemical stability of Ti3C2/ZIF-8 and its printability was tested indicating widespread application potential in coating preparation through ultrasonic spray technology. Finally, we show methods to regulate and control coating thickness and roughness for precision manufacturing. These analyses together emphasize the application value of Ti3C2/ZIF-8 in fields such as gas-storage, gas-separation, and environmental monitoring.

Continuous and Scalable Synthesis of Prussian Blue Analogues with Tunable Structure and Composition in Surfactant-Free Microreactor for Stable Zinc-Ion Storage.

We represent a segmented flow surfactant-free microfluidic strategy for continuous synthesis of Prussian blue analogues (PBAs) with high dispersity and high crystallization. Representative zinc hexacyanoferrate (ZnHCF) nanocubes were successfully synthesized in a microfluidic reactor within a few minutes via the cooperation method and possessed lower contents of crystal water and Fe(CN)6 3- vacancies than that of synthesis in bulk solution. The nucleation and particle growth process can be precisely controlled by the exploration of different flow rates and reaction temperatures during the formation of ZnHCF nanocubes in segmented flow microfluidic reactors. High crystallinity, low crystal water and vacancies in the ZnHCF structure were presented at relatively high temperatures for the crystal growth process. High-quality ZnHCF with a low content of crystal water showed excellent electrochemical activity and stability towards zinc-ion storage. The continuous and scalable synthesis approach can be extended to the fabrication of other PBAs such as NiHCF, CoHCF, MnHCF, and CuHCF with high dispersity without using any surfactants. The controllable construction of PBAs with tunable properties in microfluidic reactors provides a promising direction to minimize the gap between commercial reality and laboratory research.

New polynuclear compounds based on N-methyliminodipropionic acid: Solution studies, synthesis and X-ray crystal structures

Six new polynuclear coordination compounds based on 3d transition metal ions (Cu(II), Ni(II)) and Zn(II) with the flexible dicarboxylate compound N-methyliminodipropionic acid (H2midp) were prepared and characterized by IR spectroscopy, elemental analysis and single-crystal X-ray diffraction. Four of these compounds are 1D coordination polymers, namely [Cu(midp)(H2O)] (1), [Cu3(midp)2(H2O)4](NO3)2·6H2O (2) [Cu3(midp)2(H2O)4](CF3SO3)2·4H2O (3) and [NaZn(Hmidp)2](CF3SO3) (6). The structural analysis revealed that the chain structure of 1 is composed of [Cu(midp)(H2O)] units connected by the free carboxylato oxygen atom of neighbor units, in an alternate fashion. In 2 and 3, on the other hand, there are two [Cu(midp)H2O] units, connected by a central Cu(II) ion coordinating again to the free oxygen atom of the carboxylato groups. The Zn(II) compound is heteronuclear and the complex adopts a 1D cationic polymeric structure with zinc and sodium ions connected by two Hmidp– anions. The two other compounds are dinuclear, [Cu2(Hmidp)2(μ-H2O)2(H2O)2](CF3SO3)2·6H2O (4) and ([Ni2(midp)2(H2O)4] (5). Additionally, a Co(II) and a Cu(II) coordination compound were obtained with the same ligand and characterized by IR spectroscopy, thermal analysis and elemental analysis including metal quantification. For the copper compound the formula [Cu(Hmidp)](ClO4)·3H2O (7) is proposed while for the Co(II) compound (8) the proposed formula is [Co(midp)(H2O)2]. Solution studies of the ligand–M(II) systems (M(II) = Mn, Fe, Co, Ni, Cu, Zn, Cd and Pb) were also carried out in order to help the selection of the best synthetic conditions and also to complement the structural knowledge in the exploration of the potential formation of coordination polymers in these systems.

Physiological response of Metarhizium rileyi with linoleic acid supplementation

Metarhizium rileyi has a broad biocontrol spectrum but is highly sensitive to abiotic factors. A Colombian isolate M. rileyi Nm017 has shown notorious potential against Helicoverpa zea. However, it has a loss of up to 22 % of its conidial germination after drying, which limits its potential as a biocontrol agent and further commercialization. Conidial desiccation resistance can be enhanced by nutritional supplements, which promotes field adaptability and facilitates technological development as a biopesticide. In this study, the effect of culture medium supplemented with linoleic acid on desiccation tolerance in Nm017 conidia was evaluated. Results showed that using a 2 % linoleic acid-supplemented medium increased the relative germination after drying by 41 % compared to the control treatment, without affecting insecticidal activity on H. zea. Also, the fungus increased the synthesis of trehalose, glucose, and erythritol during drying, independently of linoleic acid use. Ultrastructural analyses of the cell wall-membrane showed a loss of thickness by 22 % and 25 %, in samples obtained from 2 % linoleic acid supplementation and the control, respectively. Regarding its morphological characteristics, conidia inner area from both treatments did not change after drying. However, conidia from the control had a 24 % decrease in length/width ratio, whereas there was no alteration in conidia from acid linoleic. The average value of dry conidia elasticity coefficient from linoleic acid treatment was 200 % above the control. Medium supplementation with linoleic acid is a promising fermentation strategy for obtaining more tolerant conidia without affecting production and biocontrol parameters, compatible solutes synthesis, or modifying its cell configuration.

Unveiling Crucial Chemical Processing Parameters Influencing the Performance of Solution-Processed Inorganic Thermoelectric Materials.

Production of thermoelectric materials from solution-processed particles involves the synthesis of particles, their purification and densification into pelletized material. Chemical changes that occur during each one of these steps render them performance determining. Particularly the purification steps, bypassed in conventional solid-state synthesis, are the cause for large discrepancies among similar solution-processed materials. In present work, the investigation focuses on a water-based surfactant free solution synthesis of SnSe, a highly relevant thermoelectric material. We show and rationalize that the number of leaching steps, purification solvent, annealing, and annealing atmosphere have significant influence on the Sn : Se ratio and impurity content in the powder. Such compositional changes that are undetectable by conventional characterization techniques lead to distinct consolidated materials with different types and concentration of defects. Additionally, the profound effect on their transport properties is demonstrated. We emphasize that understanding the chemistry and identifying key chemical species and their role throughout the process is paramount for optimizing material performance. Furthermore, we aim to demonstrate the necessity of comprehensive reporting of these steps as a standard practice to ensure material reproducibility.

Unveiling Crucial Chemical Processing Parameters Influencing the Performance of Solution‐Processed Inorganic Thermoelectric Materials

AbstractProduction of thermoelectric materials from solution‐processed particles involves the synthesis of particles, their purification and densification into pelletized material. Chemical changes that occur during each one of these steps render them performance determining. Particularly the purification steps, bypassed in conventional solid‐state synthesis, are the cause for large discrepancies among similar solution‐processed materials. In present work, the investigation focuses on a water‐based surfactant free solution synthesis of SnSe, a highly relevant thermoelectric material. We show and rationalize that the number of leaching steps, purification solvent, annealing, and annealing atmosphere have significant influence on the Sn : Se ratio and impurity content in the powder. Such compositional changes that are undetectable by conventional characterization techniques lead to distinct consolidated materials with different types and concentration of defects. Additionally, the profound effect on their transport properties is demonstrated. We emphasize that understanding the chemistry and identifying key chemical species and their role throughout the process is paramount for optimizing material performance. Furthermore, we aim to demonstrate the necessity of comprehensive reporting of these steps as a standard practice to ensure material reproducibility.

Visible-light harvesting SrTiO3 solid solutions for photocatalytic hydrogen evolution from water.

The fabrication of solid solutions represents a compelling approach to modulating the physicochemical properties of materials. In this study, we achieved the successful synthesis of solid solutions comprising SrTiO3 and SrTaO2N (denoted as (SrTiO3)1-x-(SrTaO2N)x, 0 ≤ x ≤ 1) using the magnesium powder-assisted nitridation method. The absorption edge of (SrTiO3)1-x-(SrTaO2N)x is tunable from 500 to 600 nm. The conduction band minimum (CBM) of (SrTiO3)1-x-(SrTaO2N)x comprises the Ti 3d orbitals and the Ta 5d orbitals, while the valence band maximum (VBM) consists of the O 2p and N 2p orbitals. The microstructure of the (SrTiO3)1-x‑(SrTaO2N)x consists of small nanoparticles, exhibiting a larger specific surface area than the parent compounds of SrTiO3 and SrTaO2N. In the photocatalytic hydrogen evolution reaction (HER) with sacrificial reagents, the activity of solid solutions is notably superior to that of nitrogen-doped SrTiO3 and SrTaO2N. This superiority is mainly attributed to its broad light absorption range and high charge separation efficiency, which indicates its potential as a promising photocatalytic material. Moreover, the magnesium powder-assisted nitridation method exhibits obvious advantages for the synthesis of oxynitrides and bears instructional significance for the synthesis of other nitrogen-containing compounds and even sulfur-containing compounds.

From Dopant to Host: Solution Synthesis and Light‐Emitting Applications of Organic‐Inorganic Lanthanide‐Based Metal Halides

The rich and unique energy level structure arising from 4fn inner shell configuration of trivalent lanthanide ions (Ln3+) renders them highly attractive for light‐emitting applications. Currently, research primarily focuses on Ln3+ doping in either traditional garnets or the recently developed perovskite phosphors. However, there have been few reports on stable phosphors crystallized with pure lanthanide elements. Herein, a universal solution‐based route to eight Ln3+‐based metal halides from the organic‐inorganic A4LnX7 family is described, where A+ = 4,4‐difluoropiperidinium (DFPD+), Ln3+ = Nd3+, Eu3+, Ho3+, Sm3+, Tm3+, Tb3+, Yb3+, Er3+, and X− = Cl−, Br−. Visible photoluminescence (PL) is observed from Tb3+‐, Eu3+‐, Ho3+‐, and Sm3+‐based compounds with Tb and Eu compositions exhibiting high PL quantum yields of 90–100%; Nd3+‐, Tm3+‐, Yb3+‐, and Er3+‐based crystals show fascinating near‐infrared emission. Light‐emitting diodes (LEDs) fabricated with (DFPD)4TbCl7 yield characteristic emission of Tb3+, representing the first demonstration of electroluminescence from these organic‐inorganic Ln3+‐based metal halides. Moreover, these materials exhibit distinct excitation wavelength‐dependent emission after alloying with different Ln3+ ions, making them interesting for multicolor display and multilevel information encryption applications. It is foreseen that this study will open up the way to a possible design of robust optoelectronic devices based on lanthanide metal halides.

Bifunctional octadentate pseudopeptides as Zirconium-89 chelators for immuno-PET applications

BackgroundPositron emission tomography (PET) is a highly sensitive method that provides fine resolution images, useful in the field of clinical diagnostics. In this context, Zirconium-89 (89Zr)-based imaging agents have represented a great challenge in molecular imaging with immuno-PET, which employs antibodies (mAbs) as biological vectors. Indeed, immuno-PET requires radionuclides that can be attached to the mAb to provide stable in vivo conjugates, and for this purpose, the radioactive element should have a decay half-life compatible with the time needed for the biodistribution of the immunoglobulin. In this regard, 89Zr is an ideal radioisotope for immuno-PET because its half-life perfectly matches the in vivo pharmacokinetics of mAbs.ResultsThe main objective of this work was the design and synthesis of a series of bifunctional octadentate pseudopeptides able to generate stable 89Zr complexes. To achieve this, here we investigated hydroxamate, N-methylhydroxamate and catecholate chelating moieties in complexing radioactive zirconium. N-methylhydroxamate proved to be the most effective 89Zr-chelating group. Furthermore, the increased flexibility and hydrophilicity obtained by using polyoxyethylene groups spacing the hydroxamate units led to chelators capable of rapidly forming (15 min) stable and water-soluble complexes with 89Zr under mild reaction conditions (aqueous environment, room temperature, and physiological pH) that are mandatory for complexation reactions involving biomolecules. Additionally, we report challenge experiments with the competitor ligand EDTA and metal ions such as Fe3+, Zn2+ and Cu2+. In all examined conditions, the chelators demonstrated stability against transmetallation. Finally, a maleimide moiety was introduced to apply one of the most promising ligands in bioconjugation reactions through Thiol-Michael chemistry.ConclusionCombining solid phase and solution synthesis techniques, we identified novel 89Zr-chelating molecules with a peptide scaffold. The adopted chemical design allowed modulation of molecular flexibility, hydrophilicity, as well as the decoration with different zirconium chelating groups. Best results in terms of 89Zr-chelating properties were achieved with the N-methyl hydroxamate moiety. The Zirconium complexes obtained with the most effective compounds were water-soluble, stable to transmetallation, and resistant to peptidases for at least 6 days. Further studies are needed to assess the potential of this novel class of molecules as Zirconium-chelating agents for in vivo applications.

Design, synthesis and Characterization of a novel antiferroelectric solid solution (1-x)PbHfO3-xBiAlO3

Antiferroelectric (AFE) materials are potentially useful for energy storage applications. Lead hafnate (PbHfO3) is one of the prototypical AFE materials. However, its critical field (Ecr) which is needed to induce the AFE to ferroelectric phase transition is close to the dielectric breakdown strength. To reduce Ecr, we prepare the solid solutions of (1-x)PbHfO3–xBiAlO3 (x = 0.00–0.04) via solid state synthesis. The crystal structures, dielectric behaviour, ferroelectric properties, and energy storage properties are investigated. A temperature-composition phase diagram is established. At room temperature, the crystal symmetry of all compositions is orthorhombic with the Pbam space group. Upon heating, the transition to the AFE orthorhombic Imma phase is observed at the temperature TC1, which slightly decreases with increasing x, followed by the transition to the cubic phase at the temperature TC2, which does not depend on x. Distinct dielectric anomalies are observed at TC1 and TC2. It is found that BiAlO3 substitution reduces Ecr and the polarization–electric field relations display characteristic double hysteresis loops. For x = 0.04, at a comparatively small applied field of 130 kV/cm, the values of recoverable energy density (Wrec) and efficiency of 0.24 J/cm3 and 84 %, respectively, are obtained. At 190 °C, a Wrec = 0.75 J/cm3 and a very high efficiency of 92 % are obtained at the field of 50 kV/cm. Thus, the prepared material can potentially be used in high-temperature pulsed power capacitors for energy storage applications within the temperature range from room temperature up to 190 °C.

Hydrogen-bonded frameworks based on hetero-trimers and -tetramers of octahedral cluster unit [Ta6Cl12(CN)6]3− and Mn complexes

Octahedral tantalum chlorido-cyanido cluster units, [Ta6Cl12(CN)6]4- and [Ta6Cl12(CN)6]3-, were synthesized from Ta6Cl14⋅8H2O via solution syntheses, yielding [Me4N]4[Ta6Cl12(CN)6] (1) and [Na3(MeCN)2(H2O)4][Ta6Cl12(CN)6] (2). 1 and 2 reacted with two distinct [MnIII(SB)]+ complexes (SB: a Schiff-base ligand) to produce [Me4N]{[Mn(H2O)(salen)]2[Ta6Cl12(CN)6]} ·2H2O (3) (salen2-= bis(salicylidene)ethylenediamine) and [Mn(acen)(H2O)]3[Ta6Cl12(CN)6]· 4EtOH·2H2O (4) (acen2- = bis(acetylacetonato)ethylenediamine). Single-crystal X-ray diffraction (SCXRD) and PXRD analyses confirmed the structures of all compounds. 1 is an ionic compound built of [Me4N]+ and [Ta6Cl12(CN)6]4-. 2 exhibits a neutral three-dimensional (3D) Prussian-blue structure composed of trinuclear [Na3(MeCN)2(H2O)4]3+ and hexanuclear [Ta6Cl12(CN)6]3- interconnected by CN–. 3 features a 3D hydrogen-bonded framework comprising heterotrimers {[Mn(H2O)(salen)]2[Ta6Cl12(CN)6]}- balanced by [Me4N]+. 4 possesses a 1D hydrogen-bonded structure formed by neutral heterotetramers {[Mn(acen)(H2O)]3[Ta6Cl12 (CN)6]}. Their UV–Vis, IR, thermal behaviors are discussed.

Titanium Dioxide Nanomaterial Ink Production Through Laser Ablation Synthesis in Solution for Printed Electronics Applications

Flexible and printed electronics have become increasingly popular as they make possible the production of flexible, low‐cost, multifunction devices that are unachievable through traditional manufacturing methods. The printed films are significantly impacted and thus limited by the existing ink production process. Herein, an alternate technique of generating high‐quality titanium dioxide (TiO2) nanoparticle ink compatible with aerosol jet printing using laser ablation synthesis in solution (LASiS) is showcased. Dynamic light scattering data and transmission electron microscopy confirm the particle size distribution. UV–vis measurements are performed, and the Beer–Lambert relationship is used to determine the concentration of the generated ink. The inks generated at two different repetition rates are compared: 200 kHz and 1 MHz. X‐Ray diffraction analysis of the aerosol jet printed thin film post‐thermal sintering confirms the grain size and phase purity of the printed thin films. This work demonstrates the effectiveness of the LASiS technique in producing printable nanoparticle inks with little‐to‐no postprocessing.

Robust Red-Absorbing Donor-Acceptor Stenhouse Adduct Photoswitches.

Donor-Acceptor Stenhouse Adduct (DASA), a class of push-pull negative photochrome, has received large interest lately owing to its versatile synthesis, modularity and excellent photoswitching in solutions. From a technological perspective, it is imperative for this class of photoswitches to work robustly in solid state, e. g. thin films. We feature a molecular framework for the optimized design of DASAs by introducing a new thioindoline donor (D3) and assessing its performance against known 2nd generation indoline-based donors. The systematic structure-function investigations suggest that to achieve robust reversible photoswitching, a ground state with low charge separation is desired. DASAs with stronger electron donors and a larger charge separation in the ground state result in a low population of the photothermalstationary state (PTSS) and reduced photostability. The DASA with thioindoline donor (D3A3) seems to be a special case among the donor series as it causes a red shift (ca. 15 nm), however with less polarization of the ground state and marginally better photostability as compared to the unsubstituted 2-methyl indoline (D1A3). We also emphasize the consideration of the key additional factors that can modulate the red-light photoswitching properties of DASA chromophores in polymer thin films, which might not be dominant in homogenous solution state.