Selective photoredox direct arylations of aryl bromides in water in a microfluidic reactor.

Carrying out photoredox direct arylation couplings between aryl halides and aryls in aqueous solutions of surfactants enables unprecedented selectivity with respect to the competing dehalogenation process, thanks to the partition coefficient of the selected sacrificial base. The use of a microfluidic reactor dramatically improves the reaction time, without eroding the yields and selectivity. The design of a metal free sensitizer, which also acts as the surfactant, sizeably improves the overall sustainability of arylation reactions and obviates the need for troublesome purification from traces of metal catalysts. The generality of the method is investigated over a range of halides carrying a selection of electron withdrawing and electron donating substituents.

Sustainable Access to π-Conjugated Molecular Materials via Direct (Hetero)Arylation Reactions in Water and under Air.

Direct (hetero)arylation (DHA) is playing a key role in improving the efficiency and atom economy of C-C cross coupling reactions, so has impacts in pharmaceutical and materials chemistry. Current research focuses on further improving the generality, efficiency and selectivity of the method through careful tuning of the reaction conditions and the catalytic system. Comparatively fewer studies are dedicated to the replacement of the high-boiling-point organic solvents dominating the field and affecting the overall sustainability of the method. We show herein that the use of a 9:1 v/v emulsion of an aqueous Kolliphor 2 wt% solution while having toluene as the reaction medium enables the preparation of relevant examples of thiophene-containing π-conjugated building blocks in high yield and purity.

Triplet-triplet annihilation based photon up-conversion in hybrid molecule-semiconductor nanocrystal systems.

Photon up-conversion based on triplet-triplet annihilation (TTA) exploits the annihilation of optically dark triplets of an organic emitter to produce high-energy singlets that generate high energy emission. In recently proposed hybrid systems, the annihilating triplets are indirectly sensitized by light-harvesting semiconductor colloidal nanocrystals via energy transfer from their capping ligands (h-sTTA). Here, we discuss quantitatively the performance of the h-sTTA up-conversion mechanism in a reference nanocrystal/organic emitter pair, by introducing a kinetic model that points out the relationship between the up-conversion yield and the excitation intensity. This model highlights the fundamental properties of the employed moieties that mostly affect the conversion efficiency. We derive a new expression for the excitation threshold specific for h-sTTA up-conversion, which allows us to estimate a priori the material performances from a few key parameters and to point out the most severe bottlenecks. The obtained results demonstrate that the up-conversion yield is mainly limited by ultrafast non-radiative recombinations of the optical excitons created on nanocrystals, which are competitive to the sensitization channel for emitter triplets in solution. Our results suggest that the quenching partially arises from charge transfer interactions between nanocrystals and surface ligands. Improved ligand design and optimized surface functionalization strategies are required to avoid energy losses and enhance the up-conversion performance, thus promoting the application of h-sTTA up-conversion materials in solar technologies.

Suzuki-Miyaura Micellar One-Pot Synthesis of Symmetrical and Unsymmetrical 4,7-Diaryl-5,6-difluoro-2,1,3-benzothiadiazole Luminescent Derivatives in Water and under Air.

The Suzuki-Miyaura cross-coupling reaction of 4,7-dibromo-5,6-difluoro-2,1,3-benzothiadiazole with different arylboronic acids can be efficiently carried out in water and under air by means of micellar coupling. The careful tuning of reaction conditions enables preparation of symmetrically and unsymmetrically substituted derivatives. The moderate to good yields obtained, along with the wide variety of available substitution patterns, makes this sustainable methodology very useful for the preparation of building blocks for luminescent optoelectronic materials.

π-Conjugated zwitterions as paradigm of donor-acceptor building blocks in organic-based materials.

The very peculiar characteristics of zwitterions, as well as a clearand unambiguous definition, have been overlooked in past literature. However, these compounds are particularly important in view of the impact they have had in the recent past and will likely continue to have in the future as components of performing functional organic and hybrid materials. In this Account, we primarily aim to define critically important organic concepts of zwitterions regarding both their design and nomenclature. We will particularly focus on a specific kind of zwitterions we define as π-conjugated zwitterions. These types of zwitterions are systems pertaining to the class ofdonor-acceptor (push-pull) molecules. In the ground state, they are preferentially represented in terms of an electron donor moiety bearing a negative net charge, and electron acceptor one bearing a positive net charge connected by a conjugated bridge. As such, they are possibly the most effective example of push-pull structure, possessing relevant features for applications like nonlinear optics, photovoltaics, imaging, and high capacitance dielectrics. In addition, the interaction between these dipolar compounds and the environment is highly specific and can be exploited in the construction of well-organized nanostructures, both in solution and in the solid state. According to the Gold Book of IUPAC for nomenclature, the distinction between zwitterions and the charged molecule called a betaine is subtle. The betaine is a particular class of zwitterion possessing an onium atom not bearing a hydrogen. The two terms are often considered equivalent, thus generating confusion while retrieving literature. In this Account, we define and describe π-conjugated zwitterions systems that are dipolar in the ground state, admitting resonance limiting structures that are neutral and chargeless. For the purpose of this Account and to the benefit of researchers striving to retrieve materials-related zwitterion literature data, we suggest to use the term π-zwitterions instead of the commonly used plain term "zwitterions". We show that this definition enables the clear identification of a class of compounds having unique properties distinct from "dipolar conjugated compounds." We describe the most common donor and acceptor groups in π-zwitterions. In particular, we focus our attention on the special case of the nitrile functionality, which tends to be contiguous to a negative charge. We also address special emphasis to benzenoid components that are substituted by heteroaromatic units in π-zwitterions, because the HOMO-LUMO energetic consequences are specifically involved in these cases. We make reference to the paradigmatic case of π-zwitterions second order nonlinear optical properties. Here, the value of the first hyperpolarizability ß versus the alternation in bond length turns out to be a measure of the balance of the chargeless and the dipolar contribution to the description of the zwitterion ground state. We also report literature data, collected both from our group and others, concerning π-zwitterions containing heteroaromatic and/or nitrile groups, those based on the most performing acceptors so far described, and merocyanines. With particular reference to merocyanines, we show how π-zwitterions can play a fundamental role in the fast growing field of organic photovoltaics. Finally, we present π-zwitterions made up of heteroaromatic groups that open new scenarios in heteroaromatic chemistry.

Air-Stable Perylene Diimide Trimer Material for N-Type Organic Electrochemical Transistors.

A new method is reported to make air-stable n-type organic mixed ionic-electronic conductor (OMIEC) films for organic electrochemical transistors (OECTs) using a solution-processable small molecule helical perylene diimide trimer, hPDI[3]-C11. Alkyl side chains are attached to the conjugated core for processability and film making, which are then cleaved via thermal annealing. After the sidechains are removed, the hPDI[3] film becomes less hydrophobic, more ordered, and has a deeper lowest unoccupied molecular orbital (LUMO). These features provide improved ionic transport, greater electronic mobility, and increased stability in air and in aqueous solution. Subsequently, hPDI[3]-H is used as the active material in OECTs and a device with a transconductance of 44 mS, volumetric capacitance of ≈250 F cm-3, µC* value of 1 F cm-1 V-1 s-1, and excellent stability (> 5 weeks) is demonstrated. As proof of their practical applications, a hPDI[3]-H-based OECTs as a glucose sensor and electrochemical inverter is utilized. The approach of side chain removal after film formation charts a path to a wide range of molecular semiconductors to be used as stable, mixed ionic-electronic conductors.

Correction: Chitosan-gated organic transistors printed on ethyl cellulose as a versatile platform for edible electronics and bioelectronics.

Correction for 'Chitosan-gated organic transistors printed on ethyl cellulose as a versatile platform for edible electronics and bioelectronics' by Alina S. Sharova et al., Nanoscale, 2023, 15, 10808-10819, https://doi.org/10.1039/D3NR01051A.

Nanoactuator for Neuronal Optoporation.

Light-driven modulation of neuronal activity at high spatial-temporal resolution is becoming of high interest in neuroscience. In addition to optogenetics, nongenetic membrane-targeted nanomachines that alter the electrical state of the neuronal membranes are in demand. Here, we engineered and characterized a photoswitchable conjugated compound (BV-1) that spontaneously partitions into the neuronal membrane and undergoes a charge transfer upon light stimulation. The activity of primary neurons is not affected in the dark, whereas millisecond light pulses of cyan light induce a progressive decrease in membrane resistance and an increase in inward current matched to a progressive depolarization and action potential firing. We found that illumination of BV-1 induces oxidation of membrane phospholipids, which is necessary for the electrophysiological effects and is associated with decreased membrane tension and increased membrane fluidity. Time-resolved atomic force microscopy and molecular dynamics simulations performed on planar lipid bilayers revealed that the underlying mechanism is a light-driven formation of pore-like structures across the plasma membrane. Such a phenomenon decreases membrane resistance and increases permeability to monovalent cations, namely, Na+, mimicking the effects of antifungal polyenes. The same effect on membrane resistance was also observed in nonexcitable cells. When sustained light stimulations are applied, neuronal swelling and death occur. The light-controlled pore-forming properties of BV-1 allow performing "on-demand" light-induced membrane poration to rapidly shift from cell-attached to perforated whole-cell patch-clamp configuration. Administration of BV-1 to ex vivo retinal explants or in vivo primary visual cortex elicited neuronal firing in response to short trains of light stimuli, followed by activity silencing upon prolonged light stimulations. BV-1 represents a versatile molecular nanomachine whose properties can be exploited to induce either photostimulation or space-specific cell death, depending on the pattern and duration of light stimulation.

Activation of Solid-State Emission and Photostability through Molecular Confinement: The Case of Triptycene-Fused Quinacridone Dyes.

We report the facile, metal-free convergent synthesis and the characterization of novel quinacridone dyes in which two triptycene units end-cap and sterically confine the quinacridone chromophore. A precise comparison of the confined dyes with their known homologues reveals that the reduction of π-π interactions in triptycene-fused quinacridone dyes compared to classical quinacridone results not only in an increase of solubility and processability but also in an enhancement of fluorescence quantum yield and photostability in the solid state.

Multigram-Scale Synthesis of Luminescent Cesium Lead Halide Perovskite Nanobricks for Plastic Scintillators.

Cesium lead halide perovskite nanocrystals of general formula CsPbX3 are having tremendous impact on a vast array of technologies requiring strong and tunable luminescence across the visible range and solutions processing. The development of plastic scintillators is just one of the many relevant applications. The syntheses are relatively simple but generally unsuitable to produce a large amount of material of reproducible quality required when moving from proof-of-concept scale to industrial applications. Wastes, particularly large amounts of lead-contaminated toxic and flammable organic solvents, are also an open issue. We describe a simple and reproducible procedure enabling the synthesis of luminescent CsPbX3 nanobricks of constant quality on a scale going from 0.12 to 8 g in a single batch. We also show complete recycling of the reaction wastes, leading to dramatically improved efficiency and sustainability.

Green solvents, materials, and lead-free semiconductors for sustainable fabrication of perovskite solar cells.

Perovskite materials research has received unprecedented recognition due to its applications in photovoltaics, LEDs, and other large area low-cost electronics. The exceptional improvement in the photovoltaic conversion efficiency of Perovskite solar cells (PSCs) achieved over the last decade has prompted efforts to develop and optimize device fabrication technologies for the industrial and commercial space. However, unstable operation in outdoor environments and toxicity of the employed materials and solvents have hindered this proposition. While their optoelectronic properties are extensively studied, the environmental impacts of the materials and manufacturing methods require further attention. This review summarizes and discusses green and environment-friendly methods for fabricating PSCs, particularly non-toxic solvents, and lead-free alternatives. Greener solvent choices are surveyed for all the solar cell films, (i.e. electron and hole transport, semiconductor, and electrode layers) and their impact on thin film quality, morphology and device performance is explored. We also discuss lead content in perovskites, its environmental impact and sequestration routes, and progress in replacing lead with greener alternatives. This review provides an analysis of sustainable green routes in perovskite solar cell fabrication, discussing the impact of each layer in the device stack, via life cycle analysis.

A membrane intercalating metal-free conjugated organic photosensitizer for bacterial photodynamic inactivation.

Photodynamic inhibition (PDI) of bacteria represents a powerful strategy for dealing with multidrug-resistant pathogens and infections, as it exhibits minimal development of antibiotic resistance. The PDI action stems from the generation of a triplet state in the photosensitizer (PS), which subsequently transfers energy or electrons to molecular oxygen, resulting in the formation of reactive oxygen species (ROS). These ROS are then able to damage cells, eventually causing bacterial eradication. Enhancing the efficacy of PDI includes the introduction of heavy atoms to augment triplet generation in the PS, as well as membrane intercalation to circumvent the problem of the short lifetime of ROS. However, the former approach can pose safety and environmental concerns, while achieving stable membrane partitioning remains challenging due to the complex outer envelope of bacteria. Here, we introduce a novel PS, consisting of a metal-free donor-acceptor thiophene-based conjugate molecule (BV-1). It presents several advantageous features for achieving effective PDI, namely: (i) it exhibits strong light absorption due to the conjugated donor-acceptor moieties; (ii) it exhibits spontaneous and stable membrane partitioning thanks to its amphiphilicity, accompanied by a strong fluorescence turn-on; (iii) it undergoes metal-free intersystem crossing, which occurs preferentially when the molecule resides in the membrane. All these properties, which we rationalized via optical spectroscopies and calculations, enable the effective eradication of Escherichia coli, with an inhibition concentration that is below that of current state-of-the-art treatments. Our approach holds significant potential for the development of new PS for controlling bacterial infections, particularly those caused by Gram-negative bacteria.

Chitosan-gated organic transistors printed on ethyl cellulose as a versatile platform for edible electronics and bioelectronics.

Edible electronics is an emerging research field targeting electronic devices that can be safely ingested and directly digested or metabolized by the human body. As such, it paves the way to a whole new family of applications, ranging from ingestible medical devices and biosensors to smart labelling for food quality monitoring and anti-counterfeiting. Being a newborn research field, many challenges need to be addressed to realize fully edible electronic components. In particular, an extended library of edible electronic materials is required, with suitable electronic properties depending on the target device and compatible with large-area printing processes, to allow scalable and cost-effective manufacturing. In this work, we propose a platform for future low-voltage edible transistors and circuits that comprises an edible chitosan gating medium and inkjet-printed inert gold electrodes, compatible with low thermal budget edible substrates, such as ethylcellulose. We report the compatibility of the platform, characterized by critical channel features as low as 10 µm, with different inkjet-printed carbon-based semiconductors, including biocompatible polymers present in the picogram range per device. A complementary organic inverter is also demonstrated with the same platform as a proof-of-principle logic gate. The presented results offer a promising approach to future low-voltage edible active circuitry, as well as a testbed for non-toxic printable semiconductors.

Ultrafast and Radiation-Hard Lead Halide Perovskite Nanocomposite Scintillators.

The use of scintillators for the detection of ionizing radiation is a critical aspect in many fields, including medicine, nuclear monitoring, and homeland security. Recently, lead halide perovskite nanocrystals (LHP-NCs) have emerged as promising scintillator materials. However, the difficulty of affordably upscaling synthesis to the multigram level and embedding NCs in optical-grade nanocomposites without compromising their optical properties still limits their widespread use. In addition, fundamental aspects of the scintillation mechanisms are not fully understood, leaving the scientific community without suitable fabrication protocols and rational guidelines for the full exploitation of their potential. In this work, we realize large polyacrylate nanocomposite scintillators based on CsPbBr3 NCs, which are synthesized via a novel room temperature, low waste turbo-emulsification approach, followed by their in situ transformation during the mass polymerization process. The interaction between NCs and polymer chains strengthens the scintillator structure, homogenizes the particle size distribution and passivates NC defects, resulting in nanocomposite prototypes with luminescence efficiency >90%, exceptional radiation hardness, 4800 ph/MeV scintillation yield even at low NC loading, and ultrafast response time, with over 30% of scintillation occurring in the first 80 ps, promising for fast-time applications in precision medicine and high-energy physics. Ultrafast radioluminescence and optical spectroscopy experiments using pulsed synchrotron light further disambiguate the origin of the scintillation kinetics as the result of charged-exciton and multiexciton recombination formed under ionizing excitation. This highlights the role of nonradiative Auger decay, whose potential impact on fast timing applications we anticipate via a kinetic model.

Tuning delocalization in the radical cations of 1,4-bis[4-(diarylamino)styryl]benzenes, 2,5-bis[4-(diarylamino)styryl]thiophenes, and 2,5-bis[4-(diarylamino)styryl]pyrroles through substituent effects.

Radical cations have been generated for 10 bis[4-(diarylamino)styryl]arenes and heteroarenes to investigate the effect of the electron-richness of the terminal groups and of the bridging (hetero)arene on delocalization. The intervalence charge-transfer bands of these radical cations vary from weak broad Gaussians, indicative of localized class-II mixed-valence species, to strong relatively narrow asymmetric bands, characteristic of delocalized class-III bis(diarylamino) species, to narrow symmetric bands in cases where the bridge contribution to the singly occupied molecular orbital is largest. Hush analysis of these bands yields estimates of the electronic coupling varying from 480 cm(-1) (electron-poor bridge, most electron-rich terminal aryl groups) to 1000 cm(-1) (electron-rich bridge, least electron-rich termini) if the diabatic electron-transfer distance, R(ab), is equated to the N-N separation. Computational and electron spin resonance (ESR) evidence for displacement of the diabatic states into the bridge (reduced R(ab)) suggests that these values are underestimates and that even more variation is to be expected through the series. Several dications have also been studied. The vis-NIR absorption of the dication of (E,E)-1,4-bis{4-[bis(4-n-butoxyphenyl)amino]styryl}-2,5-dicyanobenzene is seen at an energy similar to that of the strongest band in the spectrum of the corresponding weakly coupled monocation, with approximately twice the absorptivity, and its ESR spectrum suggests essentially noninteracting radical centers. In contrast, the electronic spectra of class-III monocations show no clear relationship to those of the corresponding dications, which ESR reveals to be singlet species.

NIR emitting ytterbium chelates for colourless luminescent solar concentrators.

A new oxyiminopyrazole-based ytterbium chelate enables NIR emission upon UV excitation in colorless single layer luminescent solar concentrators for building integrated photovoltaics.

Effects of Molecular Encapsulation on the Photophysical and Charge Transport Properties of a Naphthalene Diimide Bithiophene Copolymer.

Engineering the molecular structure of conjugated polymers is key to advancing the field of organic electronics. In this work, we synthesized a molecularly encapsulated version of the naphthalene diimide bithiophene copolymer PNDIT2, which is among the most popular high charge mobility organic semiconductors in n-type field-effect transistors and non-fullerene acceptors in organic photovoltaic blends. The encapsulating macrocycles shield the bithiophene units while leaving the naphthalene diimide units available for intermolecular interactions. With respect to PNDIT2, the encapsulated counterpart displays an increased backbone planarity. Molecular encapsulation prevents preaggregation of the polymer chains in common organic solvents, while it permits π-stacking in the solid state and promotes thin film crystallinity through an intermolecular-lock mechanism. Consequently, n-type semiconducting behavior is retained in field-effect transistors, although charge mobility is lower than in PNDIT2 due to the absence of the fibrillar microstructure that originates from preaggregation in solution. Hence, molecularly encapsulating conjugated polymers represent a promising chemical strategy to tune the molecular interaction in solution and the backbone conformation and to consequently control the nanomorphology of casted films without altering the electronic structure of the core polymer.

Partition of the Reactive Species of the Suzuki-Miyaura Reaction between Aqueous and Micellar Environments.

The Suzuki-Miyaura reaction between the aryl halide (1) and the phenyl boronic acid (2), in the presence of the palladium(0) complex (3) as catalyst, gives the cross-coupling product (4) in quantitative yield when performed in basic aqueous solution of the nonionic surfactant Kolliphor-EL (K-EL). The partition between the aqueous and micellar environments of the species of this reaction has been investigated by means of Molecular Dynamics (MD) simulations. Starting from the K-EL molecules dispersed in water, a micelle model has been generated by MD simulations, adopting the 2016H66 force field. Reagent and product species have been described with the same force field, once the reliability of this force field has been tested comparing the n-octanol/water partition free energies calculated from the MD and Free Energy Perturbation (FEP) method with those obtained from the quantum-mechanical SMD method. The potential of mean force for the transfer process between water and the micellar phase of the different species has been calculated by the MD simulations and the Umbrella Sampling (US) method. The overall picture that emerges from these results confirms that the molecular species involved in this reaction prefers the micellar environment and concentrates in different but close zones of the micelle. This supports the experimental evidence that the use of suitable surfactant agents promotes reactivity, allowing micelles to behave as nanoreactors in which reactive species are solubilized and enhance their local concentration.

Phase Transition toward a Thermodynamically Less Stable Phase: Cross-Nucleation due to Thin Film Growth of a Benzothieno-benzothiophene Derivative.

The molecule 2-decyl-7-phenyl-[1]benzothieno[3,2-b][1]benzothiophene is an organic semiconductor, with outstanding properties in terms of molecular packing and its use in organic electronics. The asymmetric shape of the molecule causes a double layer crystal structure at room temperature. In this work we report its thin film growth by physical vapor deposition starting from the monolayer regime up to thick films. The films are studied in terms of their morphology, crystallographic properties, and thermal stability by atomic force microscopy and X-ray diffraction methods. It is found that the bulk molecular packing of the bilayer is formed at the initial thin film growth stage. After a thickness of one double layer, a transition into a new polymorph is observed which is of metastable character. The new phase represents a single layer phase; the crystal structure could be solved by a combination of X-ray diffraction and molecular dynamics simulations. The observed thin film growth is outstanding in terms of surface crystallization: the formation of a metastable phase is not associated with the initial thin film growth, since the first growth stage represents rather the bulk crystal structure of this molecule. Its formation is associated with cross-nucleation of one polymorph by another, which explains why a metastable phase can be formed on top of a thermodynamically more stable phase.

Cold Crystallization of the Organic n-Type Small Molecule Semiconductor 2-Decyl-7-phenyl-[1]benzothieno[3,2-b][1]benzothiophene S,S,S',S'-Tetraoxide.

The asymmetric n-type Ph-BTBT-C10 derivative 2-decyl-7-phenyl-[1]benzothieno[3,2-b][1]benzothiophene S,S,S',S'-tetraoxide is structurally investigated in the thin film regime. After film preparation by spin coating and physical vapor deposition, a rather disordered structure is observed, with a strong change of its internal degree of order upon heating. At 95 °C, a transition into a layered structure of upright standing molecules without any in-plane order appears, and at 135 °C, crystallization takes place. This phase information is combined with surface morphological studies and charge carrier mobility measurements to describe the structure and thin film transistor applicability of this molecule.