Perovskite-like Liquid-Crystalline Materials Based on Polyfluorinated Imidazolium Cations.

Hybrid Organic-Inorganic Halide Perovskites (HOIHPs) represent an emerging class of semiconducting materials, widely employed in a variety of optoelectronic applications. Despite their skyrocket growth in the last decade, a detailed understanding on their structure-property relationships is still missing. In this communication, we report two unprecedented perovskite-like materials based on polyfluorinated imidazolium cations. The two materials show thermotropic liquid crystalline behavior resulting in the emergence of stable mesophases. The manifold intermolecular F⋅⋅⋅F interactions are shown to be meaningful for the stabilization of both the solid- and liquid-crystalline orders of these perovskite-like materials. Moreover, the structure of the incorporated imidazolium cation was found to tune the properties of the liquid crystalline phase. Collectively, these results may pave the way for the design of a new class of halide perovskite-based soft materials.

Covalently Modified MoS2 Bearing a Hamilton-Type Receptor for Recognizing a Redox-Active Ferrocene-Barbiturate Guest via Multiple H-Bonds.

The covalent modification of the metallic phase of MoS2 with a Hamilton-type ligand is presented, transforming MoS2 to a recognition platform which is able to embrace barbiturate moieties via hydrogen bonding. The successful hydrogen bonding formation is easily monitored by simple electrochemical assessments, if a ferrocene-labeled barbiturate analogue is utilized as a proof of concept. Full spectroscopic, thermal, and electron microscopy imaging characterization is provided for the newly formed recognition system, along with valuable insights concerning the electrochemical sensing. The given methodology expands beyond the sensing applications, confidently entering the territory of supramolecular interactions on the surface of 2D transition metal dichalcogenides. The well-designed host-guest chemistry presented herein, constitutes a guide and an inspiration for hosting customized-structured functional building blocks on MoS2 and its relatives via hydrogen bonding, opening up new opportunities regarding potential applications.

Interfacing Carbon Dots for Charge-Transfer Processes.

Carbon dots (CDs) are a booming material and the most recent incomer in the big family of carbon nanostructures. Specifically, CDs are nanosized fluorescent core-shell nanoparticles with tunable absorption and emission spectra, with high solubility in aqueous media and common organic solvents. Herein, the origins and the development of these unique nanoscale structures are discussed, key synthetic routes are briefly described, and the utilization of CDs in light-induced charge-transfer schemes is mainly focused upon. Beyond the impact of the CD's surface on the photoluminescence properties, functionalization, by covalent or supramolecular means, permits controllable incorporation of new functionalities with novel photophysical properties. Furthermore, the dual nature of CDs as electron donating or electron accepting species, unveiled upon interfacing them with organic chromophores, highlights their potentiality in managing diverse charge-transfer processes. Novel mechanisms, such as symmetry-breaking photoinduced charge-transfer can be activated upon covalent functionalization of CDs with organic dyes. Without a doubt, participation of CDs in energy conversion schemes opens up a wide avenue that may lead to the development of novel prototype devices suitable for technological applications and related to photonics and optoelectronics.

First Synthesis of the Inherently Chiral Trans-4' Bisadduct of C59 N Azafullerene by Using Cyclo-[2]-dodecylmalonate as a Tether.

The multiaddition chemistry of azafullerene C59 N has been scarcely explored, and the isolation of pure bisadducts is in its infancy. Encouraged by the recent regioselective synthesis of the inherently chiral equatorialface bisadduct of C59 N, we focused on the isolation of the first trans-4 bisadduct in a simple two-step approach. The first regioselective synthesis of the trans-4 bisadduct of C59 N by using cyclo-[2]-dodecylmalonate as a tether is now reported. The newly synthesized bisadduct has C1 symmetry, as evidenced by 13 C NMR, while X-ray crystallography validated the trans-4' addition pattern. Furthermore, the inherently chiral trans-4' C59 N bisadduct was enantiomerically resolved, and the mirror-image relation of the two enantiomers was probed by circular dichroism spectroscopy. Finally, UV-Vis and redox assays suggested that the addition pattern has a reflection in the light-harvesting and redox properties of the bisadduct.

Ping-Pong Energy Transfer in Covalently Linked Porphyrin-MoS2 Architectures.

Molybdenum disulfide nanosheets covalently modified with porphyrin were prepared and fully characterized. Neither the porphyrin absorption nor its fluorescence was notably affected by covalent linkage to MoS2 . The use of transient absorption spectroscopy showed that a complex ping-pong energy-transfer mechanism, namely from the porphyrin to MoS2 and back to the porphyrin, operated. This study reveals the potential of transition-metal dichalcogenides in photosensitization processes.

Tether-Directed Regioselective Synthesis of an Equatorialface Bisadduct of Azafullerene Using Cyclo-[2]-octylmalonate.

Bisazafullerene (C59 N)2 has been functionalized under aerobic conditions with cyclo-[2]-octylmalonate through a Mannich-type reaction, furnishing the corresponding monoadduct. A regioselective tether-directed Bingel cyclopropanation reaction was then carried out on the azafullerene core to yield a single bisadduct. Spectroscopic analysis of the formed bisadduct showed it to have a C1 symmetrical structure, making it inherently chiral. Single-crystal X-ray analysis revealed the addition pattern of the azafullerene bisadduct to be equatorialface . Examination of the optical properties showed the evolution of new absorption bands, which can be used as signatures for the characterization of equatorialface bisadducts of C59 N. Finally, redox assays showed that the LUMO level of the equatorialface bisadduct was increased compared to that of the parent (C59 N)2 .

A Long-Lived Azafullerenyl Radical Stabilized by Supramolecular Shielding with a [10]Cycloparaphenylene.

A major handicap towards the exploitation of radicals is their inherent instability. In the paramagnetic azafullerenyl radical C59 N. , the unpaired electron is strongly localized next to the nitrogen atom, which induces dimerization to diamagnetic bis(azafullerene), (C59 N)2 . Conventional stabilization by introducing steric hindrance around the radical is inapplicable here because of the concave fullerene geometry. Instead, we developed an innovative radical shielding approach based on supramolecular complexation, exploiting the protection offered by a [10]cycloparaphenylene ([10]CPP) nanobelt encircling the C59 N. radical. Photoinduced radical generation is increased by a factor of 300. The EPR signal showing characteristic 14 N hyperfine splitting of C59 N. ⊂ [10]CPP was traced even after several weeks, which corresponds to a lifetime increase of >108 . The proposed approach can be generalized by tuning the diameter of the employed nanobelts, opening new avenues for the design and exploitation of radical fullerenes.

Molecular Functionalization of Two-Dimensional MoS2 Nanosheets.

Molybdenum disulfide (MoS2 ) nanosheets have attracted great scientific interest for their remarkable electronic and optical properties. During the last few years significant progress on exfoliation methods of such nanosheets allowed the development of surface functionalization in covalent or noncovalent fashion. Markedly, the chemical modification allows tailoring and tuning the optical and electronic characteristics of MoS2 , opening new avenues for the potentiality of MoS2 -based hybrids in diverse technological fields. Physisorption of organic molecules onto MoS2 through the development of numerous van der Waals interactions is the most widely approach employed for the surface noncovalent immobilization of organic species onto MoS2 nanosheets. Conversely, developed strategies for the edge and in-plane covalent functionalization of MoS2 mainly concern chemistry at S vacancies, direct C-S bond formation, and coordination of S edges at metal centers. Herein, we focus into the most representative molecular doping strategies and material designing of MoS2 -based hybrid nanostructures carrying photo- and/or electro-active components. Key points related with the exfoliation routes, the surface functionalization approaches and their impact on the electronic properties of the functionalized nanosheets are comprehensively discussed, offering a toolbox for scientists of different disciplines interested in putting a step forward in the field of transition-metal dichalcogenide-based materials.

Axially Assembled Photosynthetic Antenna-Reaction Center Mimics Composed of Boron Dipyrromethenes, Aluminum Porphyrin, and Fullerene Derivatives.

Sequential photoinduced energy transfer followed by electron transfer leading to the formation of charge separated states in a newly assembled series of supramolecular triads comprised of boron dipyrromethenes (BODIPY or BDP), aluminum porphyrin (AlTPP) and C60 is demonstrated. In the present strategy, the energy donor (BDP) and electron acceptor (C60) were axially positioned to the plane of AlTPP via the central metal. The structural integrity of the newly synthesized compounds and self-assembled systems were fully established using spectral, electrochemical and computational methods. Thermodynamic feasibility of energy transfer from 1BDP* to AlTPP and subsequent electron transfer from 1AlTPP* to generate BDP-AlTPP•+-C60•- charge separated states was derived from free-energy calculations. Occurrence of ultrafast energy transfer from 1BDP* to AlTPP was established from studies involving steady-state and time-resolved emission, as well as femtosecond transient spectroscopic techniques. The BDP-AlTPP•+-C60•- charge separated states persisted for several nanoseconds prior returning to the ground state.

Individualized p-Doped Carbon Nanohorns.

A facile approach to individualize spherically aggregated pristine carbon nanohorns (pr-CNHs) was established. Specifically, we found that treatment of pr-CNHs with chlorosulfonic acid generates positively charged polarized species, which disintegrate toward individualized carbon nanohorns (in-CNHs). Interestingly, the isolated in-CNHs were revealed to be p-doped owing to the adsorption of chlorosulfonate units. The findings were confirmed by data derived from high-resolution transmission electron microscopy imaging, Raman and ultraviolet photoemission spectroscopy, and additionally supported by theoretical calculations and thermogravimetry.

Oxone-mediated oxidative cleavage of ß-keto esters and 1,3-diketones to α-keto esters and 1,2-diketones in aqueous medium.

A versatile and highly efficient method for the direct synthesis of α-keto esters and 1,2-diketones has been developed. This approach utilizes the oxidative cleavage of a variety of ß-keto esters and 1,3-diketones mediated by an Oxone/aluminum trichloride system. The simple one-step oxidation reaction proceeded selectively in aqueous media to afford products in high yields, short reaction times, and environmentally benign conditions.

One-step covalent hydrophobic/hydrophilic functionalization of chemically exfoliated molybdenum disulfide nanosheets with RAFT derived polymers.

The covalent functionalization of chemically exfoliated molybdenum disulfide (ce-MoS2) with hydrophobic poly(methyl methacrylate) and hydrophilic poly(acrylic acid) polymers, in a single-step without additives, is presented. The nature of chemical modification and the impact on the structure of ce-MoS2 were spectroscopically investigated. Complexation of Eu3+ was accomplished on grafted polycarboxylate chains on MoS2.

Methylammonium Lead Bromide Perovskite Nano-Crystals Grown in a Poly[styrene-co-(2-(dimethylamino)ethyl Methacrylate)] Matrix Immobilized on Exfoliated Graphene Nano-Sheets.

Development of graphene/perovskite heterostructures mediated by polymeric materials may constitute a robust strategy to resolve the environmental instability of metal halide perovskites and provide barrierless charge transport. Herein, a straightforward approach for the growth of perovskite nano-crystals and their electronic communication with graphene is presented. Methylammonium lead bromide (CH3NH3PbBr3) nano-crystals were grown in a poly[styrene-co-(2-(dimethylamino)ethyl methacrylate)], P[St-co-DMAEMA], bi-functional random co-polymer matrix and non-covalently immobilized on graphene. P[St-co-DMAEMA] was selected as a bi-modal polymer capable to stabilize the perovskite nano-crystals via electrostatic interactions between the tri-alkylamine amine sites of the co-polymer and the A-site vacancies of the perovskite and simultaneously enable Van der Waals attractive interactions between the aromatic arene sites of the co-polymer and the surface of graphene. The newly synthesized CH3NH3PbBr3/co-polymer and graphene/CH3NH3PbBr3/co-polymer ensembles were formed by physical mixing of the components in organic media at room temperature. Complementary characterization by dynamic light scattering, microscopy, and energy-dispersive X-ray spectroscopy revealed the formation of uniform spherical perovskite nano-crystals immobilized on the graphene nano-sheets. Complementary photophysical characterization by UV-Vis absorption, steady-state, and time-resolved fluorescence spectroscopy unveiled the photophysical properties of the CH3NH3PbBr3/co-polymer colloid perovskite solution and verified the electronic communication within the graphene/CH3NH3PbBr3/co-polymer ensembles at the ground and excited states.

Functionalized Carbon Nanohorns as Drug Delivery Platforms.

Carbon nanohorns (CNHs) resembling a single-layered graphene sheet wrapped in a conical shape can be chemically modified in order to immobilize, carry, and release biologically active molecules. Here, we describe the major routes for the preparation of CNH-based drug delivery platforms, via covalent coupling and encapsulation, proficient to facilitate the design of sophisticated drug nanocarriers.

An ion-selective crown ether covalently grafted onto chemically exfoliated MoS2 as a biological fluid sensor.

We describe the basal plane functionalization of chemically exfoliated molybdenum disulfide (ce-MoS2) nanosheets with a benzo-15-crown-5 ether (B15C5), promoted by the chemistry of diazonium salts en route to the fabrication and electrochemical assessment of an ion-responsive electrode. The success of the chemical modification of ce-MoS2 nanosheets was investigated by infrared and Raman spectroscopy, and the amount of the incorporated crown ether was estimated by thermogravimetric analysis. Raman spatial mapping at on-resonance excitation allowed us to disclose the structural characteristics of the functionalized B15C5-MoS2 nanosheets and the impact of basal plane functionalization to the stabilization of the 1T phase of ce-MoS2. Morphological investigation of the B15C5-MoS2 hybrid was implemented by atomic force microscopy and high-resolution transmission electron microscopy. Furthermore, fast-Fourier-transform analysis and in situ energy dispersive X-ray spectroscopy revealed the crystal lattice of the modified nanosheets and the presence of crown-ether addends, respectively. Finally, B15C5-MoS2 electrodes were constructed and evaluated as ion-selective electrodes for sodium ions in aqueous solution and an artificial sweat matrix.

Robust coherent spin centers from stable azafullerene radicals entrapped in cycloparaphenylene rings.

Molecular entities with robust spin-1/2 are natural two-level quantum systems for realizing qubits and are key ingredients of emerging quantum technologies such as quantum computing. Here we show that robust and abundant spin-1/2 species can be created in situ in the solid state from spin-active azafullerene C59N cages supramolecularly hosted in crystals of [10]cycloparaphenylene ([10]CPP) nanohoops. This is achieved via a two-stage thermally-assisted homolysis of the parent diamagnetic [10]CPP⊃(C59N)2⊂[10]CPP supramolecular complex. Upon cooling, the otherwise unstable C59N˙ radical is remarkably persistent with a measured radical lifetime of several years. Additionally, pulsed electron paramagnetic resonance measurements show long coherence times, fulfilling a basic condition for any qubit manipulation, and observed Rabi oscillations demonstrate single qubit operation. These findings together with rapid recent advances on the synthesis of carbon nanohoops offer the potential to fabricate tailored cycloparaphenylene networks hosting C59N˙ centers, providing a promising platform for building complex qubit circuits.

Solution-phase molecular recognition of an azafullerene-quinoline dyad by a face-to-face porphyrin-dimer tweezer.

A face-to-face porphyrin dimer, (H2P)2 "porphyrin tweezer", was explored as a photo- and redox-responsive host for the molecular recognition of an azafullerene (C59N) derivative bearing an amphoteric pentafluoroquinoline (FQ) domain. The intramolecular electronic coupling between the FQ substituent and the C59N cage, within the newly synthesized C59N-FQ dyad was evaluated, while the neutral and protonated form of the covalently attached FQ moiety were utilized as recognition motifs for the (H2P)2 tweezer. Complementary photophysical and electrochemical techniques were applied to investigate the electronic communication between the porphyrin-dimer (H2P)2 tweezer and the azafullerene cage as mediated by the FQ unit.

Boosting perovskite nanomorphology and charge transport properties via a functional D-π-A organic layer at the absorber/hole transporter interface.

The photovoltaic efficiency and stability challenges encountered in perovskite solar cells (PSCs) were addressed by an innovative interface engineering approach involving the utilization of the organic chromophore (E)-3-(5-(4-(bis(2',4'-dibutoxy-[1,1'-biphenyl]-4-yl)amino)phenyl)thiophen-2-yl)-2-cyanoacrylic acid (D35) as an interlayer between the perovskite absorber and the hole transporter (HTM) of mesoporous PSCs. The organic D-π-A interlayer primarily improves the perovskite's crystallinity and creates a smoother perovskite/HTM interface, while reducing the grain boundary defects and inducing an energy level alignment with the adjacent layers. Champion power conversion efficiencies (PCE) as high as 18.5% were obtained, clearly outperforming the reference devices. Interestingly, the D35-based solar cells present superior stability since they preserved 83% of their initial efficiency after 37 days of storage under dark and open circuit (OC) conditions. The obtained results consolidate the multifunctional role of organic D-π-A molecules as perovskite interface modifiers towards performance enhancement and scale-up fabrication of robust PSCs.

(Photo)electrocatalysis of molecular oxygen reduction by S-doped graphene decorated with a star-shaped oligothiophene.

Heteroatom-doped graphene-based materials attract great interest as non-metal electrocatalysts for the oxygen reduction reaction (ORR). In this work, a straightforward approach was described to prepare nanoensembles of star-shaped oligothiophene 1 supramolecularly immobilized on sulfur-doped graphene sheets (SG). The 1/SG ensemble was comprehensively characterized by Raman and IR spectroscopy and morphologically imaged by HR-TEM, while the loading of 1 onto SG was estimated by TGA under an inert atmosphere. Based on detailed electrochemical and electrocatalytic assays, 1/SG was proved to be a highly efficient and stable electrocatalyst toward the ORR. The high catalytic activity of 1/SG was attributed to the (a) presence of chemical defects, induced by the insertion of electron rich sulfur within the lattice of SG, (b) existence of structural defects, due to the generation of vacancies along the carbon lattice in SG, and (c) high and homogeneous coverage of the SG surface by the sulfur-rich star-shaped oligothiophene 1. In addition, the optical properties of 1/SG were screened by UV-Vis and steady-state and time-resolved PL and the development of strong photoinduced intra-ensemble electronic interactions within the ensemble was revealed. Exploiting the latter, by photoirradiating 1/SG, a significantly improved photoelectrocatalytic activity towards the ORR was observed.