Intramolecular Triplet Diffusion Facilitates Triplet Dissociation in a Pentacene Hexamer

Triplet dynamics in singlet fission depend strongly on the strength of the electronic coupling. Covalent systems in solution offer precise control over such couplings. Nonetheless, efficient free triplet generation remains elusive in most systems, as the intermediate triplet pair 1(T1T1) is prone to triplet‐triplet annihilation due to its spatial confinement. In the solid state, entropically driven triplet diffusion assists in the spatial separation of triplets, resulting in higher yields of free triplets. Control over electronic coupling in the solid state is, however, challenging given its sensitivity to molecular packing. We have thus developed a hexameric system (HexPnc) to enable solid‐state‐like triplet diffusion at the molecular scale. This system is realized by covalently tethering three pentacene dimers to a central subphthalocyanine scaffold. Transient absorption spectroscopy, complemented by theoretical structural optimizations and steady‐state spectroscopy, reveals that triplet diffusion is indeed facilitated due to intramolecular cluster formation. The yield of free triplets in HexPnc is increased by a factor of up to 14 compared to the corresponding dimeric reference (DiPnc). Thus, HexPnc establishes crucial design aspects for achieving efficient triplet dissociation in strongly coupled systems by providing avenues for diffusive separation of 1(T1T1), while, concomitantly, retaining strong interchromophore coupling which preserves rapid formation of 1(T1T1).Efficient free triplet generation via singlet fission remains elusive in covalent systems. We have developed a hexameric pentacene system, in which three pentacene dimers are covalently linked to a central subphthalocyanine scaffold. This allows for an entropically driven triplet diffusion, resulting in higher yields of free triplets, and establishes crucial design aspects for achieving efficient triplet dissociation in strongly coupled systems. image Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/50110000165

<i>Base-Catalyzed</i> Bifunctional Addition to Amides and Imides at Low Temperature. A New Pathway for Carbonyl Hydrogenation

Mono- or dideprotonation at the N–H groups of the Noyori ketone hydrogenation catalyst <i>trans</i>-[RuH₂((<i>R</i>)-BINAP)­((<i>R</i>,<i>R</i>)-dpen)] (<b>1a</b>) yields <i>trans</i>-M­[RuH₂((<i>R</i>,<i>R</i>)-HNCH(Ph)CH(Ph)NH₂)­((<i>R</i>)-BINAP)], where M = K⁺ (<b>8-K</b>) or Li⁺ (<b>8-Li</b>), or <i>trans</i>-M₂[RuH₂((<i>R</i>,<i>R</i>)-HNCH(Ph)CH(Ph)NH)­((<i>R</i>)-BINAP)], where M = Li⁺ (<b>8-M′</b>_<b>2</b>), which have unprecedented activity toward the hydrogenation of amide and imide carbonyls at low temperatures in THF-<i>d</i>₈. Details of the origins of the enantioselection for the desymmetrization of <i>meso</i>-cyclic imides by hydrogenation with <b>8-K</b> are also described herein

<i>Base-Catalyzed</i> Bifunctional Addition to Amides and Imides at Low Temperature. A New Pathway for Carbonyl Hydrogenation

Mono- or dideprotonation at the N–H groups of the Noyori ketone hydrogenation catalyst <i>trans</i>-[RuH₂((<i>R</i>)-BINAP)­((<i>R</i>,<i>R</i>)-dpen)] (<b>1a</b>) yields <i>trans</i>-M­[RuH₂((<i>R</i>,<i>R</i>)-HNCH(Ph)CH(Ph)NH₂)­((<i>R</i>)-BINAP)], where M = K⁺ (<b>8-K</b>) or Li⁺ (<b>8-Li</b>), or <i>trans</i>-M₂[RuH₂((<i>R</i>,<i>R</i>)-HNCH(Ph)CH(Ph)NH)­((<i>R</i>)-BINAP)], where M = Li⁺ (<b>8-M′</b>_<b>2</b>), which have unprecedented activity toward the hydrogenation of amide and imide carbonyls at low temperatures in THF-<i>d</i>₈. Details of the origins of the enantioselection for the desymmetrization of <i>meso</i>-cyclic imides by hydrogenation with <b>8-K</b> are also described herein

Nuclear Magnetic Resonance Solution Structures of Lacticin Q and Aureocin A53 Reveal a Structural Motif Conserved among Leaderless Bacteriocins with Broad-Spectrum Activity

Lacticin Q (LnqQ) and aureocin A53 (AucA) are leaderless bacteriocins from <i>Lactococcus lactis</i> QU5 and <i>Staphylococcus aureus</i> A53, respectively. These bacteriocins are characterized by the absence of an N-terminal leader sequence and are active against a broad range of Gram-positive bacteria. LnqQ and AucA consist of 53 and 51 amino acids, respectively, and have 47% identical sequences. In this study, their three-dimensional structures were elucidated using solution nuclear magnetic resonance and were shown to consist of four α-helices that assume a very similar compact, globular overall fold (root-mean-square deviation of 1.7 Å) with a highly cationic surface and a hydrophobic core. The structures of LnqQ and AucA resemble the shorter two-component leaderless bacteriocins, enterocins 7A and 7B, despite having low levels of sequence identity. Homology modeling revealed that the observed structural motif may be shared among leaderless bacteriocins with broad-spectrum activity against Gram-positive organisms. The elucidated structures of LnqQ and AucA also exhibit some resemblance to circular bacteriocins. Despite their similar overall fold, inhibition studies showed that LnqQ and AucA have different antimicrobial potency against the Gram-positive strains tested, suggesting that sequence disparities play a crucial role in their mechanisms of action