Sequential chiral induction between organic and inorganic supramolecular helical assemblies for the in situ formation of chiral carbon dots.

Self-organised helical bilayers of dicationic gemini surfactants confined in helical silica nanospace were transformed in situ to carbon dots (CDots) via pyrolysis. These water-dispersible CDots exhibit electronic absorption spanning the UV and visible range and possess symmetrical circular dichroism (CD) signals, the sign of which depends on the handedness of the helices.

Redox-active ions unlock substitutional doping in halide perovskites.

Electrical doping of metal halide perovskites (MPHs) is a key step towards the use of this efficient and cost-effective semiconductor class in modern electronics. In this work, we demonstrate n-type doping of methylammonium lead iodide (CH3NH3PbI3) by the post-fabrication introduction of Sm2+. The ionic radius of the latter is similar to that of Pb2+ and can replace it without altering the perovskite crystal lattice. It is demonstrated that once incorporated, Sm2+ can act as a dopant by undergoing oxidation to Sm3+. This results in the release of a negative charge that n-dopes the material, resulting in an increase of conductivity of almost 3 orders of magnitude. Unlike substitution doping with heterovalent ions, furtive dopants do not require counterions to maintain charge neutrality with respect to the ions they replace and are thus more likely to be incorporated into the crystalline structure. The incorporation of the dopant throughout the material is evidenced by XPS and ToF-SIMS, while the XRD pattern shows no phase separation at low and medium doping concentrations. A shift of the Fermi level towards a conduction energy of 0.52 eV confirms the doping to be n-type with a charge carrier density, calculated using the Mott-Schottky method, estimated to be nearly 1017 cm-3 for the most conductive samples. Variable-temperature conductivity experiments show that the dopant is only partially ionized at room temperature due to dopant freeze-out.

Strong circularly polarized luminescence via intramolecular excited-state symmetry-breaking charge separation.

Trans-1,2-di(1-pyrenylamino)cycloxexane was found to display circularly polarized excimer emission (glum = 0.016) both in polar and non-polar solvents that is assigned to charge separation symmetry breaking on the basis of its large transition state dipole moment (12.1 D).

Chiral Binaphthalene Building Blocks for Self-Assembled Nanoscale CPL Emitters.

The introduction of biuret hydrogen-bonding sites onto chiral binaphthalene-based chromophores was investigated as a route to sub-micron-sized, vesicle-like aggregates endowed with chiroptical properties. The synthesis was conducted from the corresponding chiral 4,4'-dibromo-1,1'-bis(2-naphthol) via Suzuki-Miyaura coupling to afford luminescent chromophores whose emission spectrum could be tuned from blue to yellow-green through extension of the conjugation. For all compounds, the spontaneous formation of hollow spheres with a diameter of ca. 200-800 nm was evidenced by scanning electron microscopy, along with strong asymmetry in the circularly polarized absorption spectra. For some compounds, the emission also displayed circular polarization with values of glum = ca. 10-3 which could be increased upon aggregation.

Probing proton diffusion as a guide to environmental stability in powder-engineered FAPbI3 and CsFAPbI3 perovskites.

Formamidinium lead iodide-based solar cells show promising device reliability. The grain imperfection can be further suppressed by developing powder methodology. The water uptake capability is critical for the stability of α-formamidinium lead triiodide (FAPbI3) thin films, and elucidating the migration of hydrogen species is challenging using routine techniques such as imaging or mass spectroscopy. Here, we decipher the proton diffusion to quantify indirect monitoring of H migration by following the N-D vibration using transmission infrared spectroscopy. The technique allows a direct assessment of the perovskite degradation associated with moisture. The inclusion of Cs in FAPbI3, reveals significant differences in proton diffusion rates, attesting to its impact. CsFAPbI3's ability to block the active layer access by water molecules is five times higher than α-FAPbI3, which is significantly higher than methylammonium lead triiodide (MAPbI3). Our protocol directly probes the local environment of the material to identify its intrinsic degradation mechanisms and stability, a key requirement for optoelectronic applications.

Disentangling Excimer Emission from Chiral Induction in Nanoscale Helical Silica Scaffolds Bearing Achiral Chromophores.

The synthesis and characterization of diketopyrrolopyrroles and perylenemonoimidodiesters linked to a substituted benzoic acid in the ortho, meta, and para positions, are reported. Grafting of these dyes on the surface of chiral silica nanohelices is used to probe how the morphology of the platform at the mesoscopic level affects the induction of chiroptical properties onto achiral molecular chromophores. The grafted structures are weakly (diketopyrrolopyrroles) or strongly (perylenemonoimidodiesters) emissive, exhibiting both locally-excited state emission and a broad, structureless emission assigned to excimers. The dissymmetry factors obtained using circular dichroism highlight optimized supramolecular organization between the chromophores for enhancing the chiroptical properties of the system. In the ortho- derivatives, poor organization due to steric hindrance is reflected in a low density of chromophores on walls of the silica-nanostructures (<0.1 vs. >0.3 and up to 0.6 molecules/nm2 for the ortho and meta or para derivatives, respectively) and lower gabs values than in the other derivatives (gabs <2×10-5 vs 6×10-5 for the ortho and para derivatives, respectively). The para derivatives presented a better organization and increased values of gabs . All grafted chromophores evidence varying degrees of excimer emission which was not found to directly correlate to their grafting density.

Chiral Anthranyl Trifluoromethyl Alcohols: Structures, Oxidative Dearomatization and Chiroptical Properties.

Chiral trifluoromethyl alcohol groups were introduced at the hindered ortho positions of 9,10-diphenylanthracenes to investigate their effects on the physical properties and reactivity towards oxidative dearomatization. In such compact structures, the position in different quadrants and the preferred orientation of the -CH(OH)CF3 groups were determined by the relative and absolute configurations of each stereoisomer, respectively. As a consequence, the stereochemistry governs the organization of the H-bonded molecules in single crystals (homochiral dimers vs ribbon), whereas in chlorinated solvents, they all behave as discrete compounds. Concerning their reactivity, the stereospecific dearomative oxidation of these molecules leads to 9,10-bis-spiro-isobenzofuran-anthracenes, when using organic single-electron transfer oxidants. The chiroptical properties of the alcohols and the corresponding dearomatized products were compared and showed an important modulation of the intensity.

Photocatalyzed decarboxylation of oxamic acids under near-infrared conditions.

Photocatalyzed oxidative decarboxylation of oxamic acids under near-infrared irradiation using Os(bptpy)2(PF6)2 as catalyst is reported. The reaction was applied to the synthesis of urethanes and heterocyclic amides. Mechanistic studies and comparative penetration depths between the NIR and the visible light mediated processes are discussed.

A Red-Light-Driven CO-Releasing Complex: Photoreactivities and Excited-State Dynamics of Highly Distorted Tricarbonyl Rhenium Phthalocyanines.

A complex comprising one [Re(CO)3 ]+ unit and a phthalocyanine (Pc) ligand (Re1 Pc) is shown to function as a photo-induced CO-releasing molecule (photoCORM) in the presence of O2 and a coordinative solvent under irradiation with red light, which can deeply penetrate living tissues. Transient absorption spectroscopic measurements indicate very short excited-state lifetimes and ultrafast intersystem crossing for Re1 Pc and Re2 Pc, which contains two [Re(CO)3 ]+ units. The excited-state properties are ascribed to efficient spin-orbit coupling and large Franck-Condon factors originating from the complexes' distorted structures, that is, unsymmetric coordination of [Re(CO)3 ]+ unit(s), one of which was confirmed by single-crystal X-ray analysis of a symmetrically substituted Pc with two [Re(CO)3 ]+ units. Re1 Pc represents a promising red-light-driven photoCORM that can be applied in biological environments or therapeutic applications.

Narcissistic self-sorting of n-acene nano-ribbons yielding energy-transfer and electroluminescence at p-n junctions.

The 2,3-didecyloxy derivative of an n-type anthracene (n-BG) and a p-type tetracene (p-R) have been synthesized and their self-assembly into nano-ribbons studied. Hyperspectral fluorescence imaging revealed their narcissistic self-sorting, leading to separated nanoribbons emitting with very different colors (blue or green for n-BG, depending on the growth solvent, and red for p-R). It is unique that the usual origins of self-sorting, such as specific H-bonding, different growth kinetics, or incompatible steric hindrance can be ruled out. Hence, the narcissistic behaviour is herein proposed to originate from a so-far unconsidered cause: the discrepancy between the quadrupolar character of n-BG and dipolar character of p-R. At the p-n junctions of these nanoribbons, inter-ribbon FRET and electro-luminescence switch-on were observed by fluorescence/luminescence microscopy.

Supramolecular gating of TADF process in self-assembled nano-spheres for high-resolution OLED applications.

Acridine-based donor-acceptor chromophores exhibiting E-type delayed fluorescence were substituted with bis-biuret H-bonding motifs to induce the formation of hollow spheres which can be deposited from solution to form the active component of OLED devices. In solution, the contribution of the delayed component is sensitive to disruption of the aggregates.

Multifunctional Anthracene-Based Ni-MOF with Encapsulated Fullerenes: Polarized Fluorescence Emission and Selective Separation of C70 from C60.

We report an anthracene-based Ni-MOF [Ni(II) metal-organic framework, {[Ni(µ2-L)2Cl2]·x(C6H6)·y(MeOH)}n (1), L = anthracene-9,10-diylbis(methylene)diisonicotinate] whose crystal structure reveals the presence of hexagonal channels with a pore size of 1.4 nm that can accommodate guests such as C60 and C70. Both confocal fluorescence and Raman microscopy results are in agreement with a homogeneous distribution of fullerenes throughout the single crystals of 1. Efficient energy transfer from 1 to the fullerenes was observed, which emitted partially polarized fluorescence emission. Stronger binding between 1 and C70 versus C60 was confirmed from HPLC analysis of the dissolved material and provides a basis for the selective retention of C70 in liquid chromatography columns packed with 1.

Revisiting the mechanism responsible for the light-struck flavor in white wines and Champagnes.

The mechanism responsible for the appearance of the light-struck fault upon exposure of white wines and Champagnes to natural or artificial light is examined in light of new experiments involving methionine analogues. The latter show that the formation of volatile sulfur species upon irradiation of riboflavin in the presence of methionine in model wine solutions at pH 3 is not dependent on the existence of neighboring group stabilization of the sulfur-centered cation radical through a 5- or 6-membered cyclic intermediate. Instead, the formation of a dimer radical cation is proposed in agreement with the formation of oxidation products such as dimethyl disulfide at early reaction times and the observed steric effect upon product distribution. The limiting quantum yield for the release of sulfur atoms from a solution of methionine in model wine solutions at pH 3.5 containing riboflavin was found to be 0.26 (435 nm irradiation). No dependence of the quantum yield or product distribution on the irradiation wavelength was found over the range 365-90 nm.

Deciphering the Orientation of the Aromatic Spacer Cation in Bilayer Perovskite Solar Cells through Spectroscopic Techniques.

Slowing the degradation of perovskite-based solar cells (PSCs) is of substantial interest. We engineered the surface by introducing a hydrophobic overlayer on a three-dimensional (3D) perovskite using fluorinated or nonfluorinated aryl ammonium cation spacers. The placement of a fluoroarene cation allows the formation of a bilayer structure, that is, layered/3D perovskites. By doing so, the surface hydrophobic character increases notably by the virtue of the perfluorinated benzene moiety. The fabricated devices thereof gave higher performance and longevity than control devices in addition to boosting reliability. The fluoro-phenethylammonium iodide (FPEAI)-based devices showed lower nonradiative carrier recombination. To decipher the orientation of the spacer cation in this bilayer structure, we probed the surface by polarization-modulated infrared reflection-absorption spectroscopy and noted substantial differences in the orientation due to the presence of fluorine substitution. We hypothesize that the stronger van der Waals interactions due to the higher electronegativity in FPEAI govern the orientation and performance enhancement and act as a barrier to moisture decomposition.

Comment on "Eppur si Muove: Proton Diffusion in Halide Perovskite Single Crystals": Eppur Non si Muove: A Critical Evaluation of Proton Diffusion in Halide Perovskite Single Crystals.

A recent report by Cahen and co-workers is examined that finds the diffusion constant for proton migration in methylammonium lead triiodide single crystals to be 2 × 105 -fold greater than that previously reported by Sadhu et al. By comparing the conversion of single crystals versus microcrystalline samples, it is concluded that proton diffusion in macroscopic single crystals is accelerated by the presence of defects acting as high-diffusivity paths.

Chirality induction to achiral molecules by silica-coated chiral molecular assemblies.

Hybrid silica-organic nanohelices are used to organize a large variety of nonchiral small organic molecules or inorganic anions to nanometer-sized assemblies. Such chiral organization of achiral molecules induces chiroptical properties as detected by vibrational or electronic circular dichroism (CD), as well as from circularly polarized luminescence (CPL).

Sensing a binding event through charge transport variations using an aromatic oligoamide capsule.

The selective binding properties of a 13-mer oligoamide foldamer capsule composed of 4 different aromatic subunits are reported. The capsule was designed to recognize dicarboxylic acids through multiple-point interactions owing to a combination of protonation/deprotonation events, H-bonding, and geometrical constraints imparted by the rigidity of the foldamer backbone. Compared to tartaric acid, binding of 2,2-difluorosuccinic acid or 2,2,3,3-tetrafluorosuccinic acid resulted in symmetry breaking due to deprotonation of only one of the two carboxylic acid groups of the encapsulated species as shown by NMR studies in solution and by single-crystal X-ray diffraction in the solid state. An analogous 14-mer foldamer capsule terminated with a thiol anchoring group was used to probe the complexation event in self-assembled monolayers on Au substrates. Ellipsometry and polarization-modulation infrared absorption-reflection spectroscopy studies were consistent with the formation of a single molecule layer of the foldamer capsule oriented vertically with respect to the surface. The latter underwent smooth complexation of 2,2-difluorosuccinic acid with deprotonation of one of the two carboxylic acid groups. A significant (80-fold) difference in the charge transport properties of the monolayer upon encapsulation of the dicarboxylic acid was evidenced from conducting-AFM measurements (S = 1.1 × 10-9 vs. 1.4 × 10-11 ohm-1 for the empty and complexed capsule, respectively). The modulation in conductivity was assigned to protonation of the aromatic foldamer backbone.

Loading Linear Arrays of CuII Inside Aromatic Amide Helices.

The very stable helices of 8-amino-2-quinolinecarboxylic acid oligoamides are shown to uptake CuII ions in their cavity through deprotonation of their amide functions with minimal alteration of their shape, unlike most metallo-organic structures which generally differ from their organic precursors. The outcome is the formation of intramolecular linear arrays of a defined number of CuII centers (up to sixteen in this study) at a 3 Šdistance, forming a molecular mimic of a metal wire completely surrounded by an organic sheath. The helices pack in the solid state so that the arrays of CuII extend intermolecularly. Conductive-AFM and cyclic voltammetry suggest that electrons are transported throughout the metal-loaded helices in contrast with hole transport observed for analogous foldamers devoid of metal ions.

Supramolecular Ladder Assemblies as a Model for Probing Electronic Interactions between Multiple Stacked π-Conjugated Systems.

A series of mono-, di-, and tri-topic receptors in which H-bonding sites, complementary to those of barbituric acid (BA), are fused is used to induce the supramolecular assembly of n×m ladders containing 1, 2, or 3 triphenylenevinylene units appended with BA. The topological constraint enforced by the architectures induces through-space interactions between the electroactive moieties that are reflected in the electronic absorption and emission spectrum. The n=2, m=2 or m=3 architectures undergo two single electron oxidation events, indicative of the formation of the corresponding mono- and di-radical cation species with comproportionation constants of 340 and 70, respectively. Comparison of the electrochemical potentials suggests that the charges are delocalized over the electroactive units in the assembly.

Correction: Supramolecular gels derived from nucleoside based bolaamphiphiles as a light-sensitive soft material.

Correction for 'Supramolecular gels derived from nucleoside based bolaamphiphiles as a light-sensitive soft material' by Julie Baillet et al., Chem. Commun., 2020, 56, 3397-3400, DOI: 10.1039/D0CC00336K.