Hybrid phthalocyanine/lead sulphide nanocomposite for bistable memory switches

Asimple, one-step method is employed to produce, at room temperature, a single layer of an organicinorganic nanocomposite containing non-aggregated lead sulphide (PbS) quantum dots (QDs) embedded in a 130 nmthick solution processed film of the organic semiconductor 6PcH2 (metal-free, non-peripherally substituted octahexyl phthalocyanine) on indium tin oxide. The mean size of PbS QDs is found from x-ray diffraction and transmission electron microscopy techniques to be much smaller than the Bohr radius. Further evidence of the quantum confinement effect is provided by a blue shift in the absorption spectrum and the increased band gap of 1.95 eV with respect to bulk PbS. The current–voltage characteristics of the hybrid and pristine 6PcH2 films, both in a sandwich configuration with the aluminium top electrode, exhibit bistable switching type hysteresis. The on-off ratio of the nanocomposite device is at least three orders of magnitude higher than that for 6PcH2 organic films, while both devices operate at a very low bias voltage of 0.5 V. The inclusion of the PbS QDs into the 6PcH2 film enhances the conductivity by nearly two orders of magnitude over that of a comparable pristine 6PcH2 film due to the formation of a charge transfer complex with PbS QDs and 6PcH2 acting as acceptors and donors of electrons, respectively

Reconsidering terms for mechanisms of polymer growth: The “Step-Growth” and “Chain-Growth” Dilemma

© 2022 The Authors. Published by Royal Society of Chemistry. This is an open access article available under a Creative Commons licence. The published version can be accessed at the following link on the publisher’s website: https://doi.org/10.1039/D2PY00086EThe terms “step-growth polymerization” and “chain-growth polymerization” are used widely in both written and oral communications to describe the two main mechanisms of polymer growth. As members of the Subcommittee on Polymer Terminology (SPT) in the Polymer Division of the International Union of Pure and Applied Chemistry (IUPAC), we are concerned that these terms are confusing because they do not describe the fundamental differences in the growth of polymers by these methods. For example, both polymerization methods are comprised of a series of steps, and both produce polymer chains. In an effort to recommend comprehensive terms, a 1994 IUPAC Recommendation from the then version of SPT suggested polycondensation and polyaddition as terms for the two variants of “step-growth polymerization”, and similarly chain polymerization and condensative chain polymerization for two variants of “chain-growth polymerization.” However, these terms also have shortcomings. Adding to the confusion, we have identified a wide variety of other terms that are used in textbooks for describing these basic methods of synthesizing polymers from monomers. Beyond these issues with “step-growth” and “chain-growth,” synthesis of polymers one monomer unit at a time presents a related dilemma in that this synthetic strategy is wholly encompassed by neither of the traditional growth mechanisms. One component of the mission of IUPAC is to develop tools for the clear communication of chemical knowledge around the world, of which recommending definitions for terms is an important element. Here we do not endorse specific terms or recommend new ones; instead, we aim to convey our concerns with the basic terms typically used for classifying methods of polymer synthesis, and in this context we welcome dialogue from the broader polymer community in a bid to resolve these issues.We acknowledge IUPAC for support of this work through project 2019-027-1-400. We thank the members of SPT for helpful discussions and critical feedback in the preparation of this manuscript

Beyond “decorative” 2D supramolecular self-assembly: strategies towards functional surfaces for nanotechnology

International audience2D supramolecular self-assembly has emerged as a powerful tool in nanoscience for bottom-up fabrication of well-defined and long range ordered two-dimensional (2D) molecular nanostructures at surfaces. Following an overview of the principles of this distinctive self-assembly process, this review focusses on recent stategies developed to go beyond the surface nanopatterning and to provide functional surfaces. With an emphasis on the chemical engineering of the molecular building-blocks constituting the adlayer, we show that besides supported nanoporous networks the more promising approach lies on up-standing 3D functional build-blocks mounted on the substrate. We highlight the opportunities offered by graphene, a substrate for which the non-covalent functionalization by supramolecular self-assembly represents a way to either control its electronic properties or provide it a new functionality. Finally, future perspectives are addressed

New liquid-crystalline semiconducting (PBTTT)-based polymer : from synthesis to organic field-effect transistor properties

International audienceπ–Conjugated macromolecules have attracted much attention due particularly to their semi-conducting properties which explain their integration into organic electronic devices, such as organic light-emitting diodes (OLEDs)[1], organic photovoltaic cells (OPVs)[2] and organic field-effect transistors (OFETs)[3]. In this field, one challenge is to improve the device performances, one way being to get higher charge carrier mobility. Such enhancement can be obtained in preparing ordered materials able to form highly organized thin film morphologies from solution processing[4]. On the one hand, Poly(2,5-bis(3-alkylthiophen-2-yl)thieno[3,2-b]thiophenes)(PBTTT) derivatives demonstrated high charge carrier mobilities and are efficient materials for OFET elaboration. On the other hand, triphenylene-based discotic mesogens can spontaneously self-organize to give columnar nanostructures by the stacking of their polyaromatic cores, providing an efficient pathway for a unidirectional charge carrier transport along the column[5]. In this context, herein we designed and prepared a new macromolecular architecture based on PBTTT polymer chain as backbone and triphenylene mesogens as side groups. The obtained polymer (PBTTT-Tri) was characterized by appropriate analytical techniques (1H NMR, 13C NMR and SEC) and its thermal behavior was studied by Polarized Optical Microscopy (POM) and Differential Scanning Calorimetry (DSC). The self-organization property of PBTTT-Tri was investigated by temperature dependent Small-angle X-ray Scattering (SAXS) and Grazing-Incidence Wide-Angle X-ray Scattering (GIWAXS). The results showed that the material presents a lamellar-columnar arrangement that can be oriented on surfaces. Moreover, the preliminary charge transport properties of PBTTT-Tri in thin films were examined in OFET configuration, and a p-type conduction with a hole mobility around 1.2 x 10-5 cm2 V-1 s-1 was observed

Caractérisation optique de l'orientation complète d'une molécule unique en utilisant son absorption triplet-triplet

International audienceProgress in single molecule fluorescence experiments have enabled an in-depth characterization of fluorophores, ranging from their photophysical rates to the orientation of their emission dipole moments in three dimensions. However, one crucial spatial information remains elusive: the molecule orientation relative to its emission dipole moment. One can retrieve the latter only by the use of another non-colinear transition dipole moment. We experimentally demonstrate the optical retrieval of this information for single Terrylene (Tr) molecules in a 30 nm thin para-terphenyl matrix. We show, through second-order correlation measurements at varying excitation power and polarization, that Tr molecules experience an optically induced deshelving of their triplet states, mediated by two orthogonal intra-molecular triplet-triplet absorption dipole moments. We take advantage of these two transition dipole moments to retrieve the full orientation of the Tr molecule, employing a 3-level scheme for the molecule photophysics and analytical calculations for the exciting electric field distribution. This modelling approach enables us to accurately describe both varying power and polarization measurements, giving access to the molecule’s photophysical rates and to its complete orientation in three dimensions. This includes the orientation of the singlet emission dipole moment in the laboratory frame, and the orientation of the molecule plane with respect to the singlet emissiondipole moment.Les progrès réalisés dans les expériences de fluorescence de molécules uniques ont permis une caractérisation approfondie des fluorophores, allant de leurs taux photophysiques à l'orientation de leurs moments dipolaires d'émission en trois dimensions. Cependant, une information spatiale cruciale reste insaisissable : l'orientation de la molécule par rapport à son moment dipolaire d'émission. On ne peut retrouver cette orientation qu'en utilisant un autre moment dipolaire de transition non-colinéaire. Nous démontrons expérimentalement la récupération par l'optique de cette information pour des molécules uniques de Terrylène (Tr) dans une matrice de para-terphényle de 30 nm d'épaisseur. Nous montrons, par des mesures de corrélation du second ordre à des puissances d'excitation et des polarisations variables, que les molécules de Tr subissent une dépopulation optiquement induite de leurs états triplets, impliquant deux moments dipolaires d'absorption triplet-triplet intramoléculaires orthogonaux. Nous tirons parti de ces deux moments dipolaires de transition pour retrouver l'orientation complète de la molécule de Tr, en utilisant un schéma à trois niveaux pour la photophysique de la molécule et des calculs analytiques pour la distribution du champ électrique d'excitation. Cette modélisation nous permet de décrire avec précision les mesures en fonction de la puissance et de la polarisation, en donnant accès aux taux photophysiques de la molécule et à son orientation complète en trois dimensions. Cela inclut l'orientation du moment dipolaire d'émission singulet dans le référentiel du laboratoire et l'orientation du plan de la molécule par rapport au moment dipolaire d'émission singulet

New TADF emitters based on pyridazine for OLEDs applications

National audienceAs a new kind of a flat emitting technology, organic light-emitting diodes (OLEDs) show many improvements over liquid crystal displays (LCDs) with impressive advantages. In this context, compounds with thermally activated delayed fluorescence (TADF) properties are outstanding from their special emitting mechanism which can harvest excitons of triplet state to obtain high photoluminescence quantum yield (PLQY). Due to its advantages of heavy metal free, high efficiency, long lifetime, TADF materials have triggered a new insight into third generation organic semiconductors for OLED application.Regarding this work, several molecules of the Donor-Acceptor (DA) and / or DAD type incorporating various electro-deficient nitrogenous hearts (pyridazine, pyridine, bipyridine, bipyridazine) have been successfully prepared, their design being designed with the aim of obtaining TADF (Thermally Activated Delayed Fluorescence) emitters. Among them, pyridazine based chemical structures have been characterized by nuclear magnetic resonance (NMR) and high-resolution mass spectroscopy (HRMS). Their photophysical properties have been studied in solution and in the solid state. In these structures, intramolecular charge transfer is produced via intermolecular interactions between the D and A groups, and their study revealed that some of them exhibit a TADF character. The electroluminescence properties of the most promising compounds have also been studied in OLED configuration

Improved synthesis of non-peripherally alkyl-substituted tetrabenzotriazaporphyrins

International audienc

Phthalocyanine analogues: Unexpectedly facile access to non-peripherally substituted octaalkyl tetrabenzotriazaporphyrins, tetrabenzodiazaporphyrins, tetrabenzomonoazaporphyrins and tetrabenzoporphyrins

Controlled syntheses of phthalocyanine/benzoporphyrin hybrid structures have been achieved. We report a simple means for obtaining non-peripherally octaalkyl-substituted derivatives of tetrabenzotriazaporphyrin (TBTAP), tetrabenzodiazaporphyrin (TBDAP), tetrabenzomonoazaporphyrin (TBMAP) and tetrabenzoporphyrin (TBP) macrocycles by treating 3,6-dialkyl phthalonitriles with differing amounts of the Grignard reagent MeMgBr. This range of macrocyclic products is not obtained from corresponding reactions of a Grignard reagent with 4-substituted phthalonitriles, reported previously, or reaction of MeMgBr with a 4,5-dialkyl phthaloni-trile. Attempts to form a meso-substituted TBTAP from 3,6-dialkyl phthalonitriles by reaction with benzyl and long-chain alkyl Grignard reagents unexpectedly gave only the parent macrocycle unsubstituted at the meso position. The synthetic protocols are by far the most straightforward and convenient means to access these interesting, but scarcely studied, classes of material. The new series of substituted macrocyclic compounds, obtained as the metal-free and magnesium-and copper(II)-metallated derivatives, show trends in the UV/Vis spectra consistent with those predicted elsewhere by Kobayashi. Characterisation of the new families allows further trends to be identified as meso-nitrogen atoms are sequentially replaced by methine bridges, for example, the compounds provide novel examples of macrocyclic structures that show columnar mesophase behaviour. Single-crystal X-ray structure determinations have been obtained for three magnesium-metallated derivatives bearing eight hexyl substituents and constitute the first set of structural data obtained for such a series

Synthesis and characterization of lead metallated non-peripherally substituted octa-octyl tetrabenzo(aza)porphyrins showing face-to-face columnar stacking in the crystal phase

The full range of porphyrin-phthalocyanine hybrids can be synthesised by treatment of 1,4-dioctylphthalonitrile with varying equivalents of MeMgBr to produce mixtures favouring specific hybrid structures and the tetrabenzoporphyrin in the extreme case. The individual macrocycles can be isolated in pure form as their magnesium derivatives, and subsequently demetallated to give the parent metal-free compounds. Insertion of lead proceeded smoothly with all hybrids using lead (II) acetate. In the case of monoaza- and triaza-hybrids, the resulting materials could be recrystallised to give crystals suitable for X-ray diffraction. The crystal structures are distinctive from previously reported examples of non-peripherally substituted octaalkyl phthalocyanines and hybrids (metal-free and metallated, including with lead) and they each present infinite stacks of cofacial macrocycles linked through bridging lead ions which, as expected, lie outside of the macrocycle plane