Aggregation‐Induced Emission Rotors: Rational Design and Tunable Stimuli Response

A novel molecular design strategy is provided to rationally tune the stimuli response of luminescent materials with aggregation‐induced emission (AIE) characteristics. A series of new AIE‐active molecules (AIE rotors) are prepared by covalently linking different numbers of tetraphenylethene moieties together. Upon gradually increasing the number of rotatable phenyl rings, the sensitivity of the response of the AIE rotors to viscosity and temperature is significantly enhanced. Although the molecular size is further enlarged, the performance is only slightly improved due to slightly increased effective rotors, but with largely increased rotational barriers. Such molecular engineering and experimental results offer more in‐depth insight into the AIE mechanism, namely, restriction of intramolecular rotations. Notably, through this rational design, the AIE rotor with the largest molecular size turns out to be the most viscosensitive luminogen with a viscosity factor of up to 0.98.     

Diarylethene-containing cyclometalated platinum(II) complexes: tunable photochromism via metal coordination and rational ligand design

The synthesis, characterization, electrochemistry, photophysics and photochromic behavior of a new class of cyclometalated platinum(II) complexes [Pt(C(∧)N)(O(∧)O)] (1a-5a and 1b-5b), where C(∧)N is a cyclometalating 2-(2'-thienyl)pyridyl (thpy) or 2-(2'-thienothienyl)pyridyl (tthpy) ligand containing the photochromic dithienylethene (DTE) unit and O(∧)O is a β-diketonato ligand of acetylacetonato (acac) or hexafluoroacetylacetonato (hfac), have been reported. The X-ray crystal structures of five of the complexes have also been determined. The electrochemical studies reveal that the first quasi-reversible reduction couple, and hence the nature of lowest unoccupied molecular orbital (LUMO) of the complexes, is sensitive to the nature of the ancillary O(∧)O ligands. Upon photoexcitation, complexes 1a-3a and 1b-3b exhibit drastic color changes, ascribed to the reversible photochromic behavior, which is found to be sensitive to the substituents on the pyridyl ring and the extent of π-conjugation of the C(∧)N ligand as well as the nature of the ancillary ligand. The thermal bleaching kinetics of complex 1a has been studied in toluene at various temperatures, and the activation barrier for the thermal cycloreversion of the complex has been determined. Density functional theory (DFT) calculations have been performed to provide an insight into the electrochemical, photophysical and photochromic properties.     

DFT and k · p modelling of the phase transitions of lead and tin halide perovskites for photovoltaic cells

3D hybrid organic perovskites, CH₃NH₃PbX₃ (X = halogen), have recently been used to strongly improve the efficiency of dye sensitized solar cells (DSSC) leading to a new class of low‐cost mesoscopic solar cells. CsSnI₃ perovskite can also be used for hole conduction in DSSC. Density functional theory and GW corrections are used to compare lead and tin hybrid and all‐inorganic perovskites. The room temperature optical absorption is associated to electronic transitions between the spin–orbit split‐off band in the conduction band and the valence band. Spin–orbit coupling is about three times smaller for tin. Moreover, the effective mass of relevant band edge hole states is small (0.17). The high temperature phase sequence of CsSnI₃ leading to the room temperature orthorhombic phase and the recently reported phases of CH₃NH₃MI₃ (where M = Pb, Sn) close to the room temperature, are also studied. Tetragonal distortions from the ideal cubic phase are analysed by a k · p perturbation, including spin–orbit effect. In addition, the non‐centrosymmetric phases of CH₃NH₃MI₃ exhibit a splitting of the electronic bands away from the critical point. The present work shows that their physical properties are more similar to conventional semiconductors than to the absorbers used in DSSC. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Non-differentiable variational principles

We develop a calculus of variations for functionals which are defined on a set of non-differentiable curves. We first extend the classical differential calculus in a quantum calculus, which allows us to define a complex operator, called the scale derivative, which is the non-differentiable analogue of the classical derivative. We then define the notion of extremals for our functionals and obtain a characterization in term of a generalized Euler-Lagrange equation. We finally prove that solutions of the Schrödinger equation can be obtained as extremals of a non-differentiable variational principle, leading to an extended Hamilton's principle of least action for quantum mechanics. We compare this approach with the scale relativity theory of Nottale, which assumes a fractal structure of space-time.     

New chemosensory materials based on disubstituted polyacetylene with strong green fluorescence

A new imidazole‐containing disubstituted polyacetylene ( P1 ) with strong green fluorescence was successfully prepared through polymer reaction, which was nearly impossible to be obtained from the direct polymerization of its corresponding monomer. The polymer was soluble in common organic solvents, and its strong green fluorescence could be quenched completely by the Cu²⁺ and Co²⁺ ions, at the concentrations as low as 1.33 and 1.67 × 10⁻⁵ mol/L (0.85 and 0.92 ppm), respectively. Because of the high stability of the complex formed by cyanide and copper ions, the quenched green fluorescence of P1 by copper ions could be turned on upon the addition of trace cyanide (as low as 2.70 × 10⁻⁵ mol/L, 0.70 ppm), making P1 a new sensitive cyanide chemosensor. The results thus provided a new opportunity to develop anion chemosensors based on good cation chemosensors. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 8070–8080, 2008     

Analyse Quantitative par Spectroscopie Infrarouge a Transformee de Fourier de la Partie Minerale de Charbons. Mise au Point et Application de la Technique

Abstract

Nous reportons dans ce mémoire des résultats ?analyses quantitatives de la matière minérale de charbon du bassin minier de Gardanne (France) par spectroscopie infrarouge a Transformée de Fourier.

Les cendres basse température (LTA) sont analysées par soustractions successives de spectres de minéraux de référence prealablement identifiés par diffraction X.

Une étude préliminaire sur des mélanges de minéraux purs est présentée. Le problème de ?échantillonage et du broyage est clairement posé et montre les possibilités et les limites de la technique IRTF. ?utilisation de minéraux locaux (Argiles grises et dolomite/calcite) permet ?étude des divers sites ?exploitation du bassin de Gardanne.

Cette étude préliminaire permet ?envisager une étude plus complète du site de Gardanne et sera mise en relation avec les procédés de combustion à basse température qui favorisent un piegeage partiel du SO₂ sous forme de sulfate.

We report in this work quantitative analysis results concerning mineral matter in Gardanne coals (France) using FTIR spectroscopy. The low temperature ashes (LTA) are analysed by successive spectral substractions of reference minerals which are before identified by X-ray diffraction.

A preliminary study of several mineral mixtures is reported.

The importance of the samples preparation and of the grinding is clearly shown as the possibilities and the limits of the FTIR method.

The use of local minerals (clays, calcite/dolomite) allow us to analyse various LTA samples of Gardanne coals.

These preliminary results will be useful for a further study of Gardanne coal basin in relation with low temperature combustion process involving partial trapping of SO₂ as sulfate.     

Unusual Through‐Space Interactions between Oxygen Atoms that Mediate Inverse Morphochromism of an AIE Luminogen

We have studied the photophysics of tetrafurylethene, an aggregation‐induced emission luminogen with exceptionally short intramolecular O?O distances of 2.80 Å and a significant red‐shifted morphochromism (27 nm) when going from the aggregate to the crystal. The short O?O distances, which are substantially smaller than the sum of the van der Waals radii (3.04 Å), are due to the fact that the oxygen atoms act as an electronic bridge connecting the furan rings on opposite ends of the central double bond, giving rise to a circular delocalization of the π‐electron density across the rings. In the excited state the O?O distance is further reduced to 2.70 Å; the increased O?O interaction causes a narrowing of the HOMO–LUMO gap, resulting in the red morphochromism of the emission. Our results show the structural origin of the red‐shifted emission lies in close O?O contacts, paving the way for understanding the clusteroluminescence of oxygen‐rich non‐conjugated systems that emit visible light.     

Multifunctional AuI‐based AIEgens: Manipulating Molecular Structures and Boosting Specific Cancer Cell Imaging and Theranostics

Gold(I) N‐heterocyclic carbene (Au^I‐NHC) complexes have emerged as potential anticancer agents owing to their high cytotoxicity and stability. Integration of their above unique functions with customized aggregation‐induced emission (AIE) luminogens to achieve specific bioimaging and efficient theranostics to cancer is highly desirable but is rarely studied. Now, a series of novel Au^I‐NHC compounds were developed with AIE characteristics. A complex with a PPh₃ ligand was selected out as it could achieve both prominent specific imaging of various cancer cells and efficient inhibition of their growth with negligible toxic effects on normal cells due to the targeting binding and strong inhibition towards thioredoxin reductase. This complex could also act as a powerful radiosensitizer to boost the anticancer efficacy with performance superior to that of popularly used auranofin. It holds great potential as a specific and effective theranostic drug in cancer diagnosis and precise therapy.     

New Wine in Old Bottles: Prolonging Room-Temperature Phosphorescence of Crown Ethers by Supramolecular Interactions

Supramolecular macrocyclic hosts have long been used in smart materials. However, their triplet emission and regulation at crystal level is rarely studied. Herein, ultralong and universal room-temperature phosphorescence (RTP) is reported for traditional crown ethers. A supramolecular strategy involving chain length adjustment and morphological locking through complexation with K⁺ was explored as a general method to tune the phosphorescence lifetime in the solid state. A maximum 10-fold increase of lifetime after complex formation accompanied with by invisible to visible phosphorescence was achieved. A deep encryption based on this activated RTP strategy was also facilely fabricated. This work thus opens a new world for supramolecular macrocycles and their intrinsic guest responsiveness offers a new avenue for versatile smart luminescent materials.     

Understanding Quantum Confinement of Charge Carriers in Layered 2D Hybrid Perovskites

Layered hybrid organic perovskites (HOPs) structures are a class of low‐cost two‐dimensional materials that exhibit outstanding optical properties, related to dielectric and quantum confinement effects. Whereas modeling and understanding of quantum confinement are well developed for conventional semiconductors, such knowledge is still lacking for 2D HOPs. In this work, concepts of effective mass and quantum well are carefully investigated and their applicability to 2D HOPs is discussed. For ultrathin layers, the effective‐mass model fails. Absence of superlattice coupling and importance of non‐parabolicity effects prevents the use of simple empirical models based on effective masses and envelope function approximations. An alternative method is suggested in which 2D HOPs are treated as composite materials, and a first‐principles approach to the calculation of band offsets is introduced. These findings might also be relevant for other classes of layered 2D functional materials.