| 1. |
- Schäfer, Clara, 1992, et al.
(författare)
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Room Temperature Dye Glasses: A Guideline Toward the Fabrication of Amorphous Dye Films with Monomeric Absorption and Emission
- 2022
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Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 34:20, s. 9294-9302
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Tidskriftsartikel (refereegranskat)abstract
- The morphology of films containing photoactive materials is crucial for the performance of solid-state dye applications. Organic dyes tend to crystallize due to their usually planar molecular structure and the resulting intermolecular interactions. This leads to inhomogeneous films with crystalline, aggregated, and amorphous regions, decreasing device efficiency and complicating spectral analysis. Improving the glass-forming ability of organic dyes therefore presents a major challenge for solid-state dye applications. Here, we present a guideline to create organic dye glasses using BODIPY as a model dye. The method is based on the strategic design of BODIPY derivatives, equipped with short alkyl chains, in combination with blending of two or more derivatives. Mixing increases the entropy of the liquid state and lowers the thermodynamic driving force for crystallization as well as the kinetic fragility of the system. This enables the fabrication of homogeneous thin films without any additives. In these films, the dye molecules are trapped in a glassy state, featuring monomeric absorption and emission. This strategy leads to a BODIPY material with an amorphous character in thin films, dropcast films, and bulk. Further, the strategy is based on thermodynamics and is therefore expected to be general, enabling the transformation of any dye molecule into a glass former.
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| 2. |
- Yang, Yizhou, 1992, et al.
(författare)
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A Highly Conductive All-Carbon Linked 3D Covalent Organic Framework Film
- 2021
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Ingår i: Small. - : Wiley. - 1613-6810 .- 1613-6829. ; 17:40
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Tidskriftsartikel (refereegranskat)abstract
- Here an all-carbon linked 3D covalent organic framework (COF) is introduced by employing a templated surface reaction in a continuous flow (TSRCF). The presented method of synthesis provides spatial control over the reaction chemistry and allows for the creation of ultrasmooth COF films of desired thickness and significant crystallinity. The films show high electrical conductivity (approximate to 3.4 S m(-1)) after being doped with tetracyanoquinodimethane (TCNQ), setting a new record for 3D COF materials. The concurrence of 3D nanosized channels and high conductivity opens up for a number of hitherto unexplored applications for this class of materials, such as high surface area electrodes, electrochemical transistors, and for electronic sensing.
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| 3. |
- Yang, Yizhou, 1992, et al.
(författare)
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A self-standing three-dimensional covalent organic framework film
- 2023
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723 .- 2041-1723. ; 14:1
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Tidskriftsartikel (refereegranskat)abstract
- Covalent crystals such as diamonds are a class of fascinating materials that are challenging to fabricate in the form of thin films. This is because spatial kinetic control of bond formation is required to create covalently bonded crystal films. Directional crystal growth is commonly achieved by chemical vapor deposition, an approach that is hampered by technical complexity and associated high cost. Here we report on a liquid-liquid interfacial approach based on physical-organic considerations to synthesize an ultrathin covalent crystal film. By distributing reactants into separate phases using hydrophobicity, the chemical reaction is confined to an interface that orients the crystal growth. A molecular-smooth interface combined with in-plane isotropic conditions enables the synthesis of films on a centimeter size scale with a uniform thickness of 13 nm. The film exhibits considerable mechanical robustness enabling a free-standing length of 37 µm, as well as a clearly anisotropic chemical structure and crystal lattice alignment.
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| 4. |
- Yang, Yizhou, 1992, et al.
(författare)
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Detachable all-carbon-linked 3D covalent organic framework films for semiconductor/COF heterojunctions by continuous flow synthesis
- 2022
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Ingår i: Chem. - : Elsevier BV. - 2451-9308 .- 2451-9294. ; 8:8, s. 2217-2227
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Tidskriftsartikel (refereegranskat)abstract
- New synthetic strategies are ceaselessly being explored to fabricate covalent organic frameworks (COFs) as continuous materials with controlled morphology. However, making substrate detachable thin layers of 3D COFs, which would allow for film-based applications, has turned out to be particularly difficult. Here, we developed a substrate-catalyzed synthesis in a continuous flow method that successfully realized the fabrication of crystalline detachable all-carbon-linked 3D SBFdiyne-COF films. The key element in the method is a highly controlled interfacial reaction between the Cu substrate and a base flowing over the substrate. Benefiting from the detachability and high quality of the fabricated film, an organic semiconductor/COF heterojunction was constructed, showing high current rectification performance of 104 under forward/reverse bias.
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| 5. |
- Yang, Yizhou, 1992, et al.
(författare)
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Electroactive Covalent Organic Framework Enabling Photostimulus-Responsive Devices
- 2022
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 144:35, s. 16093-16100
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Tidskriftsartikel (refereegranskat)abstract
- Two-dimensional covalent organic frameworks (2D COFs) feature graphene-type 2D layered sheets but with a tunable structure, electroactivity, and high porosity. If these traits are well-combined, then 2D COFs can be applied in electronics to realize functions with a high degree of complexity. Here, a highly crystalline electroactive COF, BDFamide-Tp, was designed and synthesized. It shows regularly distributed pores with a width of 1.35 nm. Smooth and successive films of such a COF were fabricated and found to be able to increase the conductivity of an organic semiconductor by 103 by interfacial doping. Upon encapsulation of a photoswitchable molecule (spiropyran) into the voids of the COF layer, the resulted devices respond differently to light of different wavelengths. Specifically, the current output ratio after UV vs Vis illumination reaches 100 times, thus effectively creating on and off states. The respective positive and negative feedbacks are memorized by the device and can be reprogrammed by UV/Vis illumination. The reversible photostimulus responsivity and reliable memory of the device are derived from the combination of electroactivity and porosity of the 2D COF. This work shows the capability of 2D COFs in higher-level electronic functions and extends their possible applications in information storage. © 2022 The Authors. Published by American Chemical Society.
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| 6. |
- Mony, Jürgen, et al.
(författare)
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Interplay between Polaritonic and Molecular Trap States
- 2022
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 126:18, s. 7965-7972
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Tidskriftsartikel (refereegranskat)abstract
- Strong exciton-photon coupling exhibits the possibility to modify the photophysical properties of organic molecules. This is due to the introduction of hybrid light-matter states, called polaritons, which have unique physical and optical properties. Those strongly coupled systems provide altered excited-state dynamics in comparison to the bare molecule case. In this study, we investigate the interplay between polaritonic and molecular trap states, such as excimers. The molecules used in this study show either prompt or delayed emission from trap states. For both cases, a dear dependency on the exciton-photon energy tuning was observed. Polaritonic emission gradually increased with a concurrent removal of aggregation-induced emission when the systems were tuned toward lower energies. For prompt emission, it is not dear whether the experimental results are best explained by a predominant relaxation toward the lower polariton after excitation or by a direct excimer to polariton transition. However, for the delayed emission case, trap states are formed on the initially formed triplet manifold, making it evident that an excimer-to-polariton transition has occurred. These results unveil the possibility to control the trap state population by creating a strongly coupled system, which may form a mitigation strategy to counteract detrimental trap states in photonic applications.
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| 7. |
- Schäfer, Clara, 1992
(författare)
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A Tale of Chaos and Colour Influencing the photophysical properties and glass forming abilities of BODIPY dyes via structural modification
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Organic dyes are everyday contributors in chemistry, physics and biology. BODIPY dyes were used as model dye class in this thesis. They are well-known for their versatility, which mainly originates from the tuneability of their photophysical properties upon changes in their molecular structure. This thesis strives to deepen the knowledge of the structure-to-photophysical properties relationship of those fluorophores. Furthermore, it demonstrates how the intrinsic properties of the dye can be influenced by modifying the molecular structure. Structural homologues of the BODIPY and the aza-BODIPY class were synthesised. The homologues differ only in the bridging atom. Moreover, they are decorated with electron withdrawing and donating groups. The effects of those groups were analysed for each class individually and additionally compared within the two classes. This revealed different behaviours of the two dye classes that were previously unexplored. To strategically decrease the singlet-triplet energy gap, a BODIPY-anthracene dyad, which populates a charge separated state, and can then undergo charge recombination into the triplet state, was oligomerised. Oligomerisation in a non-conjugated fashion mimics a fixed J-aggregate thus facilitating strong exciton coupling. This lowers the singlet state of the oligomers, without having a large effect on the triplet energy. Therefore, the energy gap, which can be described as the energy loss of the system, can be decreased. Furthermore, a new dye material, a room temperature dye glass, was fabricated. BODIPY derivatives equipped with different alkyl chains were synthesised and subsequently mixed. Upon mixing the entropy of the system is increased, leading to a decrease in the materials ability to crystallise and aggregate. The material now forms an amorphous solid state, a glass, which inherits the monomeric optical properties of the dye components. The results presented in this thesis highlight that by modifying the molecular structure of a dye molecule, its intrinsic properties can be governed according to ones needs. This is of great importance for the in vivo design of dyes as well as the fabrication of new materials.
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| 8. |
- Schäfer, Clara, 1992, et al.
(författare)
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Effect of the Aza-N-Bridge and Push-Pull Moieties: A Comparative Study between BODIPYs and Aza-BODIPYs
- 2022
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Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 87:5, s. 2569-2579
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Tidskriftsartikel (refereegranskat)abstract
- In the field of fluorescent dyes, difluoroboron-dipyrromethenes (BODIPY) have a highly respected position. To predict their photophysical properties prior to synthesis and therefore to successfully design molecules specifically for one’s needs, a solid structure-function understanding based on experimental observations is vital. This work delivers a photophysical evaluation of BODIPY and aza-BODIPY derivatives equipped with different electron-withdrawing/-donating substituents. Using combinatorial chemistry, pyrroles substituted with electron-donating/-withdrawing substituents were condensed together in two different manners, thus providing two sets of molecules. The only difference between the two sets is the bridging unit providing a so far lacking comparison between BODIPYs and aza-BODIPYs structural homologues. Replacing the meso-methine bridge with an aza-N bridge results in a red-shifted transition and considerably different, temperature-activated, excited-state relaxation pathways. The effect of electron-donating units on the absorption but not emission for BODIPYs was suppressed compared to aza-BODIPYs. This result could be evident in a substitution pattern-dependent Stokes shift. The outlook of this study is a deeper understanding of the structure-optics relationship of the (aza)-BODIPY-dye class, leading to an improvement in the de novo design of tailor-made molecules for future applications. © 2022 The Authors. Published by American Chemical Society
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| 9. |
- Schäfer, Clara, 1992, et al.
(författare)
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Entropic Mixing Allows Monomeric-Like Absorption in Neat BODIPY Films
- 2020
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Ingår i: Chemistry-a European Journal. - : Wiley. - 0947-6539 .- 1521-3765. ; 26:63, s. 14295-14299
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Tidskriftsartikel (refereegranskat)abstract
- Intermolecular interactions play a crucial role in materials chemistry because they govern thin film morphology. The photophysical properties of films of organic dyes are highly sensitive to the local environment, and a considerable effort has therefore been dedicated to engineering the morphology of organic thin films. Solubilizing side chains can successfully spatially separate chromophores, reducing detrimental intermolecular interactions. However, this strategy is also significantly decreasing achievable dye concentration. Here, five BODIPY derivatives containing small alkyl chains in the alpha-position were synthesized and photophysically characterized. By blending two or more derivatives, the increase in entropy reduces aggregation and therefore produces films with extreme dye concentration and, at the same time almost solution like absorption properties. Such a film was placed inside an optical cavity and the achieved system was demonstrated to reach the strong exciton-photon coupling regime by virtue of the achieved dye concentration and sharp absorption features of the film.
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