Benzo‐extended cyclohepta[def]fluorene derivatives with very low‐lying triplet states

Open-shell non-alternant polycyclic hydrocarbons (PHs) are attracting increasing attention due to their promising applications in organic spintronics and quantum computing. Herein we report the synthesis of three cyclohepta[def]fluorene-based diradicaloids (1–3), by fusion of benzo rings on its periphery for the thermodynamic stabilization, as evidenced by multiple characterization techniques. Remarkably, all of them display a very narrow optical energy gap (Egopt=0.52–0.69 eV) and persistent stability under ambient conditions (t1/2=11.7–33.3 h). More importantly, this new type of diradicaloids possess a low-lying triplet state with an extremely small singlet–triplet energy gap, as low as 0.002 kcal mol−1, with a clear dependence on the molecular size. This family of compounds thus offers a new route to create non-alternant open-shell PHs with high-spin ground states, and opens up novel possibilities and insights into understanding the structure–property relationships

Stoerungspraevention bei Zerlegearbeiten in kerntechnischen Anlagen durch Spannungsmessung Schlussbericht

The dismantling of nuclear facilities is in progress since 20 years in Germany. Practical experiences in decommissioning have shown, that problem can occur during dismantling operations caused by release of residual stresses. In this case cutting parts or cutting tools get jammed if mechanical cutting techniques are used. The aim of this research work was to develop measuring techniques for the determination of the stress state in RPV, to predict the deformation during dismantling operations. This can serve as additional base for improved decommissioning planning and for time optimised dismantling. For determination of the stress state in components two small and inexpensive measuring techniques were new designed, for remote-controlled on-site use in atmosphere and under water. For the nondestructive determination of the directional stress state, based on the magnetostriction and the Harmonic-Analysis of alternating magnetic fields, a new developed rotating sensor is in use with a principal magnetisation direction. Because of the mainly isotropic material properties and the directional stresses, measured Harmonic values are influenced mainly by the stress state in the surface areas. In this way it is possible to determine the stress state qualitatively and the direction of principal stresses in the surface areas of the component. As an alternative to the established wire strain gauge, which remote-controlled application is still not possible under water, a new slot jet cutting strain control technique was designed. This technique detects the deformation in the surface after stresses are cut free by a water jet. So the stress state could be determined quantitatively in the surface and assessed in the depth. With the help of these two measuring techniques it is possible to characterize the stress state along a planned cutting line. The use of an adapted FEM simulation enables to calculate and determine the deformation of the cutting gap beforehand. These information can be used to work out a dismantling strategy that guarantees an undisturbed dismantling. (orig.)SIGLEAvailable from TIB Hannover: F04B1915 / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekBundesministerium fuer Bildung und Forschung (BMBF), Bonn (Germany)DEGerman

An in-depth analysis approach enabling precision single chain nanoparticle design

The synthesis of single chain nanoparticles (SCNPs) is a vibrant field in macromolecular science, enabled by a rich variety of synthetic strategies to induce macromolecular chain folding. Due to the decrease of the hydrodynamic volume upon folding, SCNP formation is typically characterized by a shift towards higher elution volumes in size exclusion chromatography (SEC). However, a step-change in the methodologies for SCNP analysis is required for the in-depth understanding of the nature of intramolecular polymer folding and internal SCNP structure, which is critical to enable their application as catalytic nanoreactors. Herein, we exploit a unique combination of small-angle neutron scattering (SANS), 19F NMR spectroscopy, and quadruple detection SEC to generate an encompassing and systematic view of the folded morphology of poly(tert-butyl acrylate) based-SCNPs as a function of their reactive group density (5, 15, and 30 mol%) and absolute molar mass (20, 50, 100 kDa). In addition to detailed morphological insights, we establish that the primary factor dictating the compaction of SCNPs is their reactive group density, which is ineffective below 5 mol%, reaching maximum compaction close to 30 mol%. The molar mass of the precursor polymers has a minor impact on how an SCNP compacts for molar masses above 20 kDa. This journal is </p

An In-Depth Analysis Approach Enabling Precision Single Chain Nanoparticle Design

The formation of single chain nanoparticles (SCNPs) is typically characterized by a shift towards higher elution volumes in SEC due to size decrease upon folding. However, a step-change in SCNP analysis is required for understanding of the nature of intramolecular SCNP folding. Herein, we exploit a unique combination of SANS, 19F NMR spectroscopy, and multidetection SEC to generate a systematic view of the folded morphology of poly(butyl acrylate) based-SCNPs as a function of their reactive group density and molar mass. In addition to detailed morphological insights, we establish that the primary factor dictating the compaction of SCNPs is their reactive group density, which is ineffective below 5 mol%, reaching maximum compaction close to 30 mol%. Above 20 kDa the molar mass of the precursor polymers has a minor impact on how an SCNP compacts

High molecular weight mechanochromic spiropyran main chain copolymers via reproducible microwave-assisted Suzuki polycondensation

Suzuki-Miyaura polycondensation (SPC) is widely used to prepare a variety of copolymers for a broad range of applications. Although SPC protocols are often used in many instances, the limits of this method and issues of molecular weight reproducibility are not often looked at in detail. By using a spiropyran-based (SP) mechanochromic copolymer, we present an optimized protocol for the microwave-assisted synthesis of a mechanochromic, alternating copolymer P(SP-alt-C-10) via SPC that allows the reproduction of molecular weight distributions. Several parameters such as microwave power, temperature, stoichiometry, and ligand are screened, leading to molecular weights up to M-w similar to 174 kg mol(-1). The process of optimization is guided by NMR end group analysis which shows that dehalogenation, oxidative deborylation and SP cleavage are the limiting factors that impede further increase of molar mass, while other classical side reactions such as protiodeborylation are not observed. Embossing films of P(SP-alt-C-10) yields the colored merocyanine (MC) copolymer P(MC-alt-C-10) that undergoes a thermally facilitated back reaction to P(SP-alt-C-10). DFT suggests that the barrier of the SP -> MC transition has two contributions, with the first one being related to the color change and the second one to internal bond reorganizations. The barrier height is 1.5 eV, which suggests that the ease of the thermally facilitated back reaction is either due to residual energy stored in the deformed polymer matrix, or arises from an MC isomer that is not in the thermodynamically most stable state

Synthesis, Purification, and Characterization of Well-Defined All-Conjugated Diblock Copolymers PF8TBT-<i>b</i>-P3HT

We present the synthesis, purification, and characterization of all-conjugated block copolymers comprising poly­((9,9-dioctylfluorene)-2,7-diyl-<i>alt</i>-[4,7-bis­(3-hexylthien-5-yl)-2,1,3-benzothiadiazole]-2′,2″-diyl) (PF8TBT) and poly­(3-hexylthiophene) (P3HT). Suzuki step-growth polycondensation is used for the synthesis of PF8TBT, which is subsequently terminated via the addition of narrow-distributed, monobrominated P3HT-Br. Purification via preparative GPC is carried out to reduce polydispersity and to remove excess P3HT. Wavelength-dependent GPC and careful NMR end group analysis, assisted by model compounds, reveal pure diblock copolymers of PF8TBT-<i>b</i>-P3HT. Insight into structure formation is given by temperature-dependent UV–vis absorption, DSC, and X-ray scattering. These indicate that PF8TBT-<i>b</i>-P3HT does not microphase-separate within the investigated range of composition and molecular weight. The critical role of introducing sufficient dissimilarity between the segments in all-conjugated block copolymers in order to induce phase separation is discussed, with the conclusion that careful tuning of side chains is crucial for achieving self-organization