Hetero-Substituted αβ-Fused BODIPY

Here, we report the synthesis and properties of heterosubtituted αβ-fused BODIPY fluorophores. The compounds were obtained in good yields by sequential and selective Stille cross-coupling reactions from 2,3,5,6-tetrahalo-BODIPY, allowing the introduction of different substituents at the 3,5 and 2,6 positions of the BODIPY ring. The final fused compounds were synthesized using oxidative cyclisation with ferrous chloride. The fully fused compounds show a strong bathochromically shifted emission along with a hyperchromic shift of the absorption maxima. The fluorescence quantum yields remain relatively large for compounds emitting in this wavelength range. Computational studies have been carried out to fully understand the photophysical behaviour of these dyes.     

An anhydrous precursor approach to BaYF5-based upconverting nanocrystals

With an objective to have easy access to high quality BaYF₅ matrix, we report here new anhydrous precursors of barium and yttrium which show a good compatibility in terms of co-thermal decomposition. These complexes not only fill the void of precursors for Ba-based upconverting (UC) nanomaterials but also provide a way to minimize the –OH concentration around these nanocrystals (NCs) to enhance their UC efficiency without requiring the usual core-shell structure. The precursors and the BaYF₅ NCs co-doped with Yb³⁺/Tm³⁺ ions were thoroughly characterized. The NCs were studied for upconversion properties and preliminary results are presented here. On the basis of these results, a mechanism for the energy transfer in Yb–Tm system is proposed.     

New two-step sequence involving a hetero-Diels-Alder and a nonphenolic oxidative coupling reaction: a convergent access to analogs of steganacin

A new family of analogs of steganacin, an important antimitotic compound, was accessed. It takes advantage of a completely stereoselective sequence of two key steps. The central dihydropyrane core is built by a highly diastereoselective and facially controlled hetero-Diels-Alder reaction. It is followed by a nonphenolic biaryl oxidative coupling with a complete atropo-stereoselectivity. It leads to a quick way to form cyclic biaryl lignans.     

Hydrogen Bonding as a Supramolecular Tool for Robust OFET Devices

In the present study, we demonstrated the effect of hydrogen bonding in the semiconducting behaviour of a small molecule used in organic field-effect transistors (OFETs). For this study, the highly soluble dumbbell-shaped molecule, Boc-TATDPP based on a Boc-protected thiophene-diketopyrrolopyrrole (DPP) and triazatruxene (TAT) moieties was used. The two Boc groups of the molecule were removed by annealing at 200 °C, which created a strong hydrogen-bonded network of NH-TATDPP supported by additional π–π stacking. These were characterised by thermogravimetric analysis (TGA), UV/Vis and IR spectroscopy, XRD and high-resolution (HR)-TEM measurements. FETs were fabricated with the semiconducting channel made of Boc-TATDPP and NH-TATDPP separately. It is worth mentioning that the Boc-TATDPP film can be cast from solution and then annealed to get the other systems with NH-TATDPP. More importantly, NH-TATDPP showed significantly higher hole mobilities compared to Boc-TATDPP. Interestingly, the high hole mobility in the case of NH-TATDPP was unaffected upon blending with [6,6]-phenyl-C71-butyric acid methyl ester (PC₇₁BM). Thus, this robust hydrogen-bonded supramolecular network is likely to be useful in designing efficient and stable organic optoelectronic devices.     

Squalyl Crown Ether Self‐Assembled Conjugates: An Example of Highly Selective Artificial K+ Channels

The natural KcsA K⁺ channel, one of the best‐characterized biological pore structures, conducts K⁺ cations at high rates while excluding Na⁺ cations. The KcsA K⁺ channel is of primordial inspiration for the design of artificial channels. Important progress in improving conduction activity and K⁺/Na⁺ selectivity has been achieved with artificial ion‐channel systems. However, simple artificial systems exhibiting K⁺/Na⁺ selectivity and mimicking the biofunctions of the KcsA K⁺ channel are unknown. Herein, an artificial ion channel formed by H‐bonded stacks of squalyl crown ethers, in which K⁺ conduction is highly preferred to Na⁺ conduction, is reported. The K⁺‐channel behavior is interpreted as arising from discreet stacks of dimers resulting in the formation of oligomeric channels, in which transport of cations occurs through macrocycles mixed with dimeric carriers undergoing dynamic exchange within the bilayer membrane. The present highly K⁺‐selective macrocyclic channel can be regarded as a biomimetic alternative to the KcsA channel.     

Tailoring of Polarizing Agents in the bTurea Series for Cross‐Effect Dynamic Nuclear Polarization in Aqueous Media

A series of 18 nitroxide biradicals derived from bTurea has been prepared, and their enhancement factors ? (¹H) in cross‐effect dynamic nuclear polarization (CE DNP) NMR experiments at 9.4 and 14.1 T and 100 K in a DNP‐optimized glycerol/water matrix (“DNP juice”) have been studied. We observe that ? (¹H) is strongly correlated with the substituents on the polarizing agents, and its trend is discussed in terms of different molecular parameters: solubility, average e–e distance, relative orientation of the nitroxide moieties, and electron spin relaxation times. We show that too short an e–e distance or too long a T_1e can dramatically limit ? (¹H). Our study also shows that the molecular structure of AMUPol is not optimal and its ? (¹H) could be further improved through stronger interaction with the glassy matrix and a better orientation of the TEMPO moieties. A new AMUPol derivative introduced here provides a better ? (¹H) than AMUPol itself (by a factor of ca. 1.2).