Colloidal quantum dots (QDs) stand among the most attractive light-harvesting materials to be exploited for solution-processed optoelectronic applications. To this aim, quantitative replacement of ...the bulky electrically insulating ligands at the QD surface coming from the synthetic procedure is mandatory. Here we present a conceptually novel approach to design light-harvesting nanomaterials demonstrating that QD surface modification with suitable short conjugated organic molecules permits us to drastically enhance light absorption of QDs, while preserving good long-term colloidal stability. Indeed, rational design of the pendant and anchoring moieties, which constitute the replacing ligand framework leads to a broadband increase of the optical absorbance larger than 300% for colloidal PbS QDs also at high energies (>3.1 eV), which could not be predicted by using formalisms derived from effective medium theory. We attribute such a drastic absorbance increase to ground-state ligand/QD orbital mixing, as inferred by density functional theory calculations; in addition, our findings suggest that the optical band gap reduction commonly observed for PbS QD solids treated with thiol-terminating ligands can be prevalently ascribed to 3p orbitals localized on anchoring sulfur atoms, which mix with the highest occupied states of the QDs. More broadly, we provide evidence that organic ligands and inorganic cores are inherently electronically coupled materials thus yielding peculiar chemical species (the colloidal QDs themselves), which display arising (opto)electronic properties that cannot be merely described as the sum of those of the ligand and core components.
Colloidal quantum dots are composed of nanometer‐sized crystallites of inorganic semiconductor materials bearing organic molecules at their surface. The organic/inorganic interface markedly affects ...forms and functions of the quantum dots, therefore its description and control are important for effective application. Herein we demonstrate that archetypal colloidal PbS quantum dots adapt their interface to the surroundings, thus existing in solution phase as equilibrium mixtures with their (metal‐)organic ligand and inorganic core components. The interfacial equilibria are dictated by solvent polarity and concentration, show striking size dependence (leading to more stable ligand/core adducts for larger quantum dots), and selectively involve nanocrystal facets. This notion of ligand/core dynamic equilibrium may open novel synthetic paths and refined nanocrystal surface‐chemistry strategies.
Colloidal quantum dots adapt their composition to their surroundings, existing in the solution phase as equilibrium mixtures with their (metal‐)organic ligand and inorganic core components. The inherently dynamic organic/inorganic interface of colloidal quantum dots may open novel possibilities towards improved synthetic procedures and effective surface‐chemistry strategies.
Phenothiazine-based compounds, PTZ1 and PTZ2, were synthesized through straightforward Buchwald–Hartwig and Suzuki–Miyaura cross-couplings, respectively, by binding the suitable donor groups ...(diarylamine or triarylamine) to a phenothiazine core. Phenothiazine-based structures were proven for the first time as hole-transporting materials in solution-processed lead trihalide perovskite-based solar cells. A dramatic effect exerted by the presence of phenylene spacers was observed on the relevant photovoltaic performances. The power conversion efficiencies measured under AM1.5 sun increase from 2.1% (PTZ1) to a remarkable 17.6% (PTZ2), a value rivaling those obtained with the state-of-the-art Spiro-OMeTAD (17.7%). These results indicate phenothiazine-based compounds as promising candidates to be used as readily available and cost-effective hole-transporting materials in perovskite solar cells.
The electronics era is flourishing and morphing itself into Internet of Everything, IoE. At the same time, questions arise on the issue of electronic materials employed: especially their natural ...availability and low-cost fabrication, their functional stability in devices, and finally their desired biodegradation at the end of their life cycle. Hydrogen bonded pigments and natural dyes like indigo, anthraquinone and acridone are not only biodegradable and of bio-origin but also have functionality robustness and offer versatility in designing electronics and sensors components. With this Perspective, we intend to coalesce all the scattered reports on the above-mentioned classes of hydrogen bonded semiconductors, spanning across several disciplines and many active research groups. The article will comprise both published and unpublished results, on stability during aging, upon electrical, chemical and thermal stress, and will finish with an outlook section related to biological degradation and biological stability of selected hydrogen bonded molecules employed as semiconductors in organic electronic devices. We demonstrate that when the purity, the long-range order and the strength of chemical bonds, are considered, then the Hydrogen bonded organic semiconductors are the privileged class of materials having the potential to compete with inorganic semiconductors. As an experimental historical study of stability, we fabricated and characterized organic transistors from a material batch synthesized in 1932 and compared the results to a fresh material batch.
A tetracoordinated redox couple, made by Cu(2-mesityl-4,7-dimethyl-1,10-phenanthroline)2PF6, 1, and its Cu(II) form Cu(2-mesityl-4,7-dimethyl-1,10-phenanthroline)2PF62, 2, has been synthesized, ...and its electrochemical and photochemical features have been investigated and compared with those of a previously published Cu2+/Cu+ redox shuttle, namely, Cu(2,9-dimethyl-1,10-phenanthroline)2PF6, 3, and its pentacoordinated oxidized form Cu(2,9-dimethyl-1,10-phenanthroline)2ClPF6, 4. The detrimental effect of the fifth Cl– ancillary ligand on the charge transfer kinetics of the redox shuttles has been exhaustively demonstrated. Appropriately balanced Cu-based electrolytes have been then formulated and tested in dye solar cells in combination with a π-extended benzothiadiazole dye. The bis-phenanthroline Cu-complexes, 1 and 2, have been found to provide an overall 4.4% solar energy conversion efficiency, which is more than twice that of the literature benchmark couple, 3 and 4, employing a Cl-coordinated oxidized species and even comparable with the performances of a I–/I3 – electrolyte of analogous concentration. A fast counter-electrode reaction, due to the excellent electrochemical reversibility of 2, and a high electron collection efficiency, allowed through the efficient dye regeneration kinetics exerted by 1, represents two major characteristics of these copper-based electron mediators and may constitute a pivotal step toward the development of a next generation of copper-based efficient iodine-free redox shuttles.
Hydrogen‐bonded pigments are remarkably stable high‐crystal lattice energy organic solids. Here a lesser‐known family of compounds, the epindolidiones, which demonstrates electronic transport with ...extraordinary stability, even in highly demanding aqueous environments, is reported. Hole mobilities in the range 0.05–1 cm2 V–1 s–1 can be achieved, with lower electron mobilities of up to 0.1 cm2 V–1 s–1. To help understand charge transport in epindolidiones, X‐ray diffraction is used to solve the crystal structure of 2,8‐difluoroepindolidione and 2,8‐dichloroepindolidione. Both derivatives crystallize with a linear‐chain H‐bonding lattice featuring two‐dimensional π–π stacking. Powder diffraction indicates that the unsubstituted epindolidione has very similar crystallinity. All types of epindolidiones measured here display strong low‐energy optical emission originating from excimeric states, which coexists with higher‐energy fluorescence. This can be exploited in light‐emitting diodes, which show the same hybrid singlet and low‐energy excimer electroluminescence. Low‐voltage FETs are fabricated with epindolidione, which operate reliably under repeated cyclic tests in different ionic solutions within the pH range 3–10 without degradation. Finally, in order to overcome the insolubility of epindolidiones in organic solvents, a chemical procedure is devised to allow solution‐processing via the introduction of suitable thermolabile solubilizing groups. This work shows the versatile potential of epindolidione pigments for electronics applications.
Epindolidiones are H‐bonded organic pigment semiconductors with excellent operational stability, including in aqueous media. Their crystal structure, electrochemical properties, and photophysics, which are dominated by excimeric effects, are reported. Transistor and light‐emitting devices are demonstrated. Routes for solution processing of epindolidiones using transient solubilizing groups are explored.
The surface chemistry of colloidal cesium lead bromide (CsPbBr
3
) nanocrystals is decisive in determining the stability and the final morphology of this class of materials, characterized by ionic ...structure and a high defect tolerance factor. Here, the high sensitivity of purified colloidal nanocubes of CsPbBr
3
to diverse environmental condition (solvent dilution, ageing, ligands post synthetic treatment) in ambient atmosphere is investigated by means of a comprehensive morphological (electron microscopy), structural (
θ
/2
θ
X-ray diffraction (XRD) and grazing incidence wide angle scattering (GIWAXS)), and spectroscopic chemical (
1
H nuclear magnetic resonance (NMR), nuclear Overhauser effect spectroscopy (NOESY), absorption and emission spectroscopy) characterization. The aging and solvent dilution contribute to modify the nanocrystal morphology, due to a modification of the ligand dynamic. Moreover, we establish the ability of aliphatic carboxylic acids and alkyl amines ligands to induce, even in a post preparative process at room temperature, structural, morphological and spectroscopic variations. Upon post synthesis alkyl amine addition, in particular of oleyl amine and octyl amine, the highly green emitting CsPbBr
3
nanocubes effectively turn into one-dimensional (1D) thin tetragonal nanowires or lead halide deficient rhombohedral zero-dimensional (0D) Cs
4
PbBr
6
structures with a complete loss of fluorescence. The addition of an alkyl carboxylic acid, as oleic and nonanoic acid, produces the transformation of nanocubes into still emitting orthorombic two-dimensional (2D) nanoplates. The acid/base equilibrium between the native and added ligands, the adsorbed/free ligands dynamic in solution and the ligand solubility in non-polar solvent contribute to render CsPbBr
3
particularly sensitive to environmental and processing conditions and, therefore prone to undergo to structural, morphological and, hence spectroscopic, transformations.
The mechanism of the Suzuki–Heck (SuHe) polymerisation of 2,7‐dibromo‐9,9‐di(n‐dodecyl)fluorene (1) with potassium vinyl trifluoroborate (PVTB) for the synthesis of poly(fluorenylene vinylene)s ...(PFVs) has been investigated. In the first stage, a palladium‐catalysed chain‐growth AA/B(C)‐type polycondensation occurs, as evidenced by the linear trend observed when plotting the molecular weights of the polymer formed against the consumption of the monomer. The chain‐growth stage takes place until complete consumption of 1 and allows one to envisage the alternating addition of PVTB (by a Suzuki step) and 1 (by a Heck step) to the growing chain. Such alternating addition seems to proceed through a peculiar catalyst transfer during which the metal is constantly bound to the growing chain, confirmed by MALDI end‐group analysis. On prolonging the reaction after the disappearance of 1, a second stage takes place, leading to higher molecular weight polymers, which are formed by the step‐growth condensation of the fragments generated in the first stage. The molecular weights of the final PFVs depend on the PVTB/1 feed ratio. Thus, by using a PVTB/1 molar ratio of 1.1, the final PFV was characterised by an Mn of 39600 Da, whereas when using a PVTB/1 molar ratio of 2.0, the final PFV was characterised by an Mn of 13200 Da.
Chain growth versus step growth: The first example of a metal‐catalysed polycondensation reaction to obtain poly(arylene vinylene)s through a chain‐growth mechanism followed by a step‐growth process is presented (see figure).
Chemical and biochemical functionalization of nanoparticles (NPs) can lead to an active cellular uptake enhancing their efficacy thanks to the targeted localization in tumors. In the present study ...calcium carbonate nano-crystals (CCNs), stabilized by an alcohol dehydration method, were successfully modified by grafting human serum albumin (HSA) on the surface to obtain a pure protein corona. Two types of CCNs were used: naked CaCO3 and the (3-aminopropyl)triethoxysilane (APTES) modified CaCO3-NH2. The HSA conjugation with naked CCN and amino-functionalized CCN (CCN-NH2) was established through the investigation of modification in size, zeta potential, and morphology by Transmission Electron Microscopy (TEM). The amount of HSA coating on the CCNs surface was assessed by spectrophotometry. Thermogravimetric analysis (TGA) and Differential scanning calorimetry (DSC) confirmed the grafting of APTES to the surface and successive adsorption of HSA. Furthermore, to evaluate the effect of protein complexation of CCNs on cellular behavior, bioavailability, and biological responses, three human model cancer cell lines, breast cancer (MCF7), cervical cancer (HeLa), and colon carcinoma (Caco-2) were selected to characterize the internalization kinetics, localization, and bio-interaction of the protein-enclosed CCNs. To monitor internalization of the various conjugates, chemical modification with fluorescein-isothiocyanate (FITC) was performed, and their stability over time was measured. Confocal microscopy was used to probe the uptake and confirm localization in the perinuclear region of the cancer cells. Flow cytometry assays confirmed that the bio-functionalization influence cellular uptake and the CCNs behavior depends on both cell line and surface features.
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