Access to dithiophene‐fused oxadiborepins and the first azadiborepins attained via a modular synthesis route are presented. The new compounds emit intense blue light, some of which demonstrate ...fluorescence quantum yields close to unity. Cyclic voltammetry (CV) revealed electrochemically reversible one‐electron reduction processes. The weak aromatic character of the novel 1,2,7‐azadiborepin ring is demonstrated with in‐depth theoretical investigations using nucleus‐independent chemical shift (NICS) scans and anisotropy of the induced current density (ACID) calculations.
Dithienooxa‐ and ‐azadiborepins are accessible in a modular way from a common precursor. These BNB‐doped polycyclic aromatic hydrocarbons (PAHs) are highly efficient blue‐light emitters with quantum yields up to 96 %. In‐depth theoretical studies reveal that the previously unknown azadiborepin ring system is weakly aromatic.
The application of our newly developed B–C coupling method by catalytic Si/B exchange is demonstrated for the synthesis of a series of triarylboranes (1), monodisperse thienyl‐ and furylborane dimers ...(2) and trimers (9), extended oligomers (3) and polymers (3′), as well as mixed (oligo)thienyl‐/furylboranes. The structures of 1 aaTip, 1 bbTip, and 2 bbbMes*, determined by X‐ray crystallography, reveal largely coplanar hetarene rings and BR3 environments, which are most pronounced in the furylborane species. Photophysical investigations, supported by TD‐DFT calculations, revealed pronounced π‐electron delocalization over the hetarene backbones including the boron centers. With an extended series of derivatives of varying chain lengths available, we were able to determine the effective conjugation lengths (ECL) of poly(thienylborane)s and poly(furylborane)s, which have been reached with the highest‐molecular‐weight derivatives of our study. Through variation of the furan‐to‐thiophene ratio, the photophysical properties of these materials are effectively modulated. Significantly, higher furan contents lead to considerably increased fluorescence intensities. Compounds 1 aaTip, 1 bbTip, and 3 aTip showed the ability to bind fluoride anions. The binding process is signaled by a distinct change in their optical absorption characteristics, thus rendering these materials attractive targets for sensory applications.
Ob‐La‐B Ob‐La‐Si: Catalytic Si/B exchange polycondensation provided access to a series of thienyl‐ and furylboranes, monodisperse oligomers, and polymers. The photophysical properties of such species are effectively modulated through variation of the ratio of the heterocycles in the backbone (see scheme).
Fully aromatic, luminescent, and highly robust BNB-doped phenalenyls have been prepared, which are isoelectronic to the phenalenyl cation.
B
-Fluoromesityl-substitution leads to fluorescence in an ...extremely narrow range and significant increase in the reduction potential. Detailed theoretical investigations revealed an intramolecular aromaticity switch upon one-electron reduction.
Fully aromatic, fluorescent, and highly robust BNB-doped phenalenyls were prepared
via
ring expansion, which undergo an aromaticity switch upon reduction.
While certain inorganic main‐group polymers such as silicones (polysiloxanes) are ubiquitous in our everyday life, poly(iminoborane)s have been elusive for a long time. Incorporation of heterocyclic ...building blocks into their backbone has recently enabled access to the first derivatives of this inorganic‐polymer class, as this approach effectively prevents undesired side‐reactions to borazines. Information about the microstructure of these cyclolinear macromolecules, however, has been scarce. Herein, we present the synthesis of a series of monodisperse oligomers with up to 7 boron and 8 nitrogen atoms, representing the longest well‐defined molecular >B=N<x chain to date. We accomplished to characterize six of them structurally in the solid state by single‐crystal X‐ray diffraction, thus providing valuable insight into the microstructure of poly(iminoborane)s. In addition, we report on the synthesis of new poly(iminoborane) derivatives featuring aryl side groups, with an increased content of unsubstituted phenyl groups. The p‐(n‐butyl)phenyl‐substituted species 13 represents the highest‐molecular‐weight sample of this class of inorganic polymers to date.
Aryl‐substituted poly(iminoborane)s and a series of monodisperse oligo(iminoborane)s with increasing number of B=N units in a chain have been prepared – including the highest‐molecular‐weight poly(iminoborane) and the longest molecular >B=N<x chain, so far. X‐ray diffraction studies gave insights into the structures of the oligomers and, hence, into the microstructures of the corresponding polymers.
Conjugated organoboranes have emerged as attractive hybrid materials for optoelectronic applications. Herein, a highly efficient, environmentally benign catalytic B–C bond formation method is ...presented that uses organosilicon compounds, dibromoboranes, and the metal-free organocatalyst Me3SiNTf2. This Si/B exchange approach has been successfully applied to the synthesis of arylborane molecules 4a–c, oligomers 8a,b, and polymers 8a′,b′. Photophysical investigations, supported by TD-DFT calculations, reveal highly effective π-conjugation in thienyl- and furylborane species; the latter are also highly emissive.
Doping of π-conjugated polymers or molecular compounds with trivalent boron atoms has recently emerged as a viable strategy to produce new materials with intriguing properties and functions. The ...combination of boron with furan moieties has been only scarcely explored so far, although the resulting furan-based materials have several notable features, including favorable optoelectronic properties and improved sustainability. Herein, we investigate the doping of α-polyfurans with a varying number of boron atoms. A series of poly(oligofuran boranes) and oligofuran-bridged bisboranes have been prepared via microwave-assisted Stille-type catalytic cross-coupling protocols. In the solid-state structures of the molecular compounds, the furan and the borane moieties exhibit a strictly coplanar arrangement; the derivative with a pentafuran bridge forms a dimeric structure in the solid state. All new compounds show considerable absorption and emission features in the visible range that arise from π–π* transitions in the oligofurylborane backbone. They are highly luminescent with quantum yields between 89 and 97% for the bisboranes and up to 87% for the difuran-bridged polymer PB2F. Their emission colors can be effectively tuned in the visible range from blue to orange via the length of the oligofuran linker. Spectroelectrochemical investigations on the difuran-bridged bisborane BB2F and polymer PB2F revealed fully reversible stepwise reductions to the respective radical anion (polaron), with absorption features in the near-infrared (NIR) region, and subsequently to a dianion (dipolaron). Overall, the doping of α-oligofurans with boron leads to a decrease of the frontier orbital energies, a reduction of the electronic band gap, and the formation of very robust and oxidatively stable materials.
Thermoresponsive polymers are frequently involved in the development of materials for various applications. Here, polymers containing poly(2‐ benzhydryl‐2‐oxazine) (pBhOzi) repeating units are ...described for the first time. The homopolymer pBhOzi and an ABA type amphiphile comprising two flanking hydrophilic A blocks of poly(2‐methyl‐2‐oxazoline) (pMeOx) and the hydrophobic aromatic pBhOzi central B block (pMeOx‐b‐pBhOzi‐b‐pMeOx) are synthesized and the latter is shown to exhibit inverse thermogelling properties at concentrations of 20 wt.% in water. This behavior stands in contrast to a homologue ABA amphiphile consisting of a central poly(2‐benzhydryl‐2‐oxazoline) block (pMeOx‐b‐pBhOx‐b‐pMeOx). No inverse thermogelling is observed with this polymer even at 25 wt.%. For 25 wt.% pMeOx‐b‐pBhOzi‐b‐pMeOx, a surprisingly high storage modulus of ≈22 kPa and high values for the yield and flow points of 480 Pa and 1.3 kPa are obtained. Exceeding the yield point, pronounced shear thinning is observed. Interestingly, only little difference between self‐assemblies of pMeOx‐b‐pBhOzi‐b‐pMeOx and pMeOx‐b‐pBhOx‐b‐pMeOx is observed by dynamic light scattering while transmission electron microscopy images suggest that the micelles of pMeOx‐b‐pBhOzi‐b‐pMeOx interact through their hydrophilic coronas, which is probably decisive for the gel formation. Overall, this study introduces new building blocks for poly(2‐oxazoline) and poly(2‐oxazine)‐based self‐assemblies, but additional studies will be needed to unravel the exact mechanism.
Novel homopolymers and amphiphilic block copolymers comprising the monomers 2‐benzhydryl‐2‐oxazoline and 2‐benzhydryl‐2‐oxazine (BhOzi) are described. While both types of amphiphilic block copolymers form well‐defined spherical micelles in water, only the amphiphilic block copolymer based on BhOzi forms a thermoresponsive hydrogels upon cooling of the aqueous solutions, presumably via increased correlation between the hydrophilic shells of the micelles.
Direct functionalization and Pd-catalyzed cross-coupling of difuryl(supermesityl)borane (1) led to highly emissive organoborane compounds 3 and 4. Photophysical and TD-DFT studies reveal an increase ...of the HOMO levels with higher hetarene content and stabilization of the HOMO and LUMO levels through B-doping, leading to very robust, air-stable electron-accepting materials.
Direct functionalization and Pd-catalyzed cross-coupling of difuryl(supermesityl)borane (
1
) led to highly emissive organoborane compounds
3
and
4
. Photophysical and TD-DFT studies reveal an ...increase of the HOMO levels with higher hetarene content and stabilization of the HOMO and LUMO levels through B-doping, leading to very robust, air-stable electron-accepting materials.
B-Doping of oligo(hetarene)s led to very robust, air-stable π-conjugated materials that are strong electron-acceptors and blue light emitters.
An oligo(iminoborane), depicted on the cover as the dinosaur, was synthesized as part of a series of monodisperse oligo(iminoborane)s with increasing number of B=N units in the chain. Herein, the ...number of backbone atoms could be extended to 7 boron and 8 nitrogen atoms. This oligomer represents the longest well‐defined molecular >B=N<x chain reported so far. The structures of the oligomers were studied by X‐ray diffractometry, also providing insight into the microstructure of poly(iminoborane)s (PIBs). In their Research Article, H. Helten and co‐workers describe PIBs with increased aromatic content, including the PIB with the highest molecular weight known to date. The meteorite collision visualizes TGA measurements of the polymers which lead to the formation of boron nitride. The authors would like to thank Tina Schneider for creating the cover artwork.
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