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Understanding charge transport in networks of 2D crystals is essential for developing reliable applications such as chemiresistors or electromagnetic shields. For this purpose, intra- and inter-flake contributions to the network resistance must be disentangled. MXenes such as Ti3C2Tx, are prime examples of 2D crystals often employed as thin networks of interconnected flakes for functional devices. While a significant number of studies focused on transport in individual MXene flakes, inter-flake transport remains scarcely explored. Here, we demonstrate that charge transport in multi-flake conductive paths of Ti3C2Tx is dominated by interflake junctions and provide quantitative estimates of junction resistances. Scanning probe measurements reveal that in a MXene multi-flake conductive path, individual flakes behave as isopotential domains, since the voltage drop is localized precisely at inter-flake junctions. The chemiresistive response to humidity is further investigated at the single flake, multi-flake and flake network scale, evidencing the crucial impact of junctions on sensing kinetics. These findings underline the dominant role of inter-flake junctions in MXene charge transport and sensing capabilities.

Self-assembly of aromatic oligoamides into multihelical structures is a powerful strategy for developing complex and functional molecular architectures. As the hybridization process is directed by the folded state of the oligomers, inducing changes in the folding can be used to control the self-assembly. As one approach for this, Diels–Alder reactions on diazaanthracene monomers allow site-specific modification of aromatic oligoamides. The reaction leads to a bend in the monomer that, in turn, distorts the structure of the oligomer. Herein, we show that this strategy can be used to control the self-assembly of the oligomers. Using reversible Diels–Alder reactions allows switching between distinct folded states with different self-assembly preferences. This strategy can be applied during oligomer synthesis to prevent self-assembly or postsynthetically to disassemble multihelical structures. In complex systems containing multiple oligomers, we show that the modification can further be used to direct social versus narcissistic self-sorting, allowing for the switch between homomeric and heteromeric double helical assemblies.

Optically addressable molecular spins aim to tackle control and detection of weak magnetic moment when magnetic devices are scaled down to the single-molecule level. To achieve accurate readout of molecular spin states by adjacent luminescent probes, the molecular design must meet the stringent requirements of both high signal-to-noise ratio (SNR) and high sensitivity. Here, we incorporated a naphthalimide-based ratiometric fluorescent (RF) probe with a donor–acceptor (D–A) structure into a spin crossover (SCO) molecule. The probe features dual emission channels arising from a locally excited (LE) state and an intramolecular charge-transfer (ICT) state. The thermochromism associated with SCO spectrally overlaps with the probe’s RF bands, producing a reverse synergistic effect, achieving ratiometric fluorescent thermometers (RFTs) with 1.35% K–1 sensitivity and 66% fluorescence contrast. More importantly, the bright fluorescence thermochromism (∼50% quantum yield) is maintained throughout the entire SCO process, enabling direct visualization of spin-state equilibria with high SNR (>400) and detection resolution (0.0017) even at low concentrations of 10–4 M. This tuning of the single-fluorophore RF against SCO thermochromism provides a new design platform for the accurate readout of spin states of molecules.

 Un siècle après l’hypothèse fondatrice selon laquelle toute particule matérielle possède un comportement ondulatoire, la physique quantique continue de révéler des aspects inattendus.

Retrouvez Matthieu Génévriez sur La Première dans Matin Première pour parler des ordinateurs quantiques. Nos e-mails, nos données bancaires ou encore les secrets de défense pourraient-ils un jour devenir lisibles par tous ? Avec l’essor de l’informatique quantique, cette question n’est plus de la science-fiction. Selon certaines prévisions, comme celles de Saxo Bank, un « Q-Day » pourrait survenir : le jour où les systèmes de chiffrement actuels ne suffiraient plus à protéger nos données numériques. Mais de quoi parle-t-on exactement ? Et faut-il s’inquiéter ?