Phosphate selective binding and sensing by halogen bonding tripodal copper(II) metallo-receptors in aqueous media.

Combining the potency of non-covalent halogen bonding (XB) with metal ion coordination, the synthesis and characterisation of a series of hydrophilic XB tripodal Cu(II) metallo-receptors, strategically designed for tetrahedral anion guest binding and sensing in aqueous media is described. The reported metallo-hosts contain a tripodal C3-symmetric tris-iodotriazole XB donor anion recognition motif terminally functionalised with tri(ethylene glycol) and permethylated ß-cyclodextrin functionalities to impart aqueous solubility. Optical UV-vis anion binding studies in combination with unprecedented quantitative EPR anion titration investigations reveal the XB Cu(II) metallo-receptors exhibit strong and selective phosphate recognition over a range of other monocharged anionic species in competitive aqueous solution containing 40% water, notably outperforming a hydrogen bonding (HB) Cu(II) metallo-receptor counterpart. Electrochemical studies demonstrate further the capability of the metallo-receptors to sense anions via significant cathodic perturbations of the respective Cu(II)/Cu(I) redox couple.

Singlet Fission in Pechmann Dyes: Planar Chromophore Design and Understanding.

Singlet fission in organic chromophores holds the potential for enhancing photovoltaic efficiencies beyond the single-junction limit. The most basic requirement of a singlet fission material is that it has a large energy gap between its first singlet and triplet excited states. Identifying such compounds is not simple and has been accomplished either through computational screening or by subtle modifications of previously known fission materials. Here, we propose an approach that leverages ground and excited-state aromaticity combined with double-bond conformation to establish simple qualitative design rules for predicting fundamental optical properties without the need for computational modeling. By investigating two Pechmann dye isomers, we demonstrate that although their planarity and degree of charge transfer are similar, singlet fission is active in the isomer with a trans-conformation, while the cis-isomer exhibits greater favorability for polaronic processes, experimentally validated using ultrafast and electron spin resonance spectroscopy. Our results offer a new design perspective that provides a rational framework for tailoring optoelectronic systems to specific applications such as singlet fission or triplet-triplet annihilation.

pH-sensitive release of nitric oxide gas using peptide-graphene co-assembled hybrid nanosheets.

Nitric oxide (NO) donating drugs such as organic nitrates have been used to treat cardiovascular diseases for more than a century. These donors primarily produce NO systemically. It is however sometimes desirable to control the amount, location, and time of NO delivery. We present the design of a novel pH-sensitive NO release system that is achieved by the synthesis of dipeptide diphenylalanine (FF) and graphene oxide (GO) co-assembled hybrid nanosheets (termed as FF@GO) through weak molecular interactions. These hybrid nanosheets were characterised by using X-ray diffraction, Raman spectroscopy, Fourier transform infrared spectroscopy, zeta potential measurements, X-ray photoelectron spectroscopy, scanning and transmission electron microscopies. The weak molecular interactions, which include electrostatic, hydrogen bonding and π-π stacking, are pH sensitive due to the presence of carboxylic acid and amine functionalities on GO and the dipeptide building blocks. Herein, we demonstrate that this formulation can be loaded with NO gas with the dipeptide acting as an arresting agent to inhibit NO burst release at neutral pH; however, at acidic pH it is capable of releasing NO at the rate of up to 0.6 µM per minute, comparable to the amount of NO produced by healthy endothelium. In conclusion, the innovative conjugation of dipeptide with graphene can store and release NO gas under physiologically relevant concentrations in a pH-responsive manner. pH responsive NO-releasing organic-inorganic nanohybrids may prove useful for the treatment of cardiovascular diseases and other pathologies.

S-nitrosocysteamine-functionalised porous graphene oxide nanosheets as nitric oxide delivery vehicles for cardiovascular applications.

Nitric oxide (NO) is a key signalling molecule released by vascular endothelial cells that is essential for vascular health. Low NO bioactivity is associated with cardiovascular diseases, such as hypertension, atherosclerosis, and heart failure and NO donors are a mainstay of drug treatment. However, many NO donors are associated with the development of tolerance and adverse effects, so new formulations for controlled and targeted release of NO would be advantageous. Herein, we describe the design and characterisation of a novel NO delivery system via the reaction of acidified sodium nitrite with thiol groups that had been introduced by cysteamine conjugation to porous graphene oxide nanosheets, thereby generating S-nitrosated nanosheets. An NO electrode, ozone-based chemiluminescence and electron paramagnetic resonance spectroscopy were used to measure NO released from various graphene formulations, which was sustained at >5 × 10-10 mol cm-2 min-1 for at least 3 h, compared with healthy endothelium (cf. 0.5-4 × 10-10 mol cm-2 min-1). Single cell Raman micro-spectroscopy showed that vascular endothelial and smooth muscle cells (SMCs) took up graphene nanostructures, with intracellular NO release detected via a fluorescent NO-specific probe. Functionalised graphene had a dose-dependent effect to promote proliferation in endothelial cells and to inhibit growth in SMCs, which was associated with cGMP release indicating intracellular activation of canonical NO signalling. Chemiluminescence detected negligible production of toxic N-nitrosamines. Our findings demonstrate the utility of porous graphene oxide as a NO delivery vehicle to release physiologically relevant amounts of NO in vitro, thereby highlighting the potential of these formulations as a strategy for the treatment of cardiovascular diseases.

Excited-State Engineering Enables Efficient Deep-Blue Light-Emitting Diodes Exhibiting BT.2020 Color Gamut.

Organic luminescent materials that exhibit thermally activated delayed fluorescence (TADF) can convert non-emissive triplet excitons into emissive singlet states through a reverse intersystem crossing (RISC) process. Therefore, they have tremendous potential for applications in organic light-emitting diodes (OLEDs). However, with the development of ultra-high definition 4K/8K display technologies, designing efficient deep-blue TADF materials to achieve the Commission Internationale de l'Éclairage (CIE) coordinates fulfilling BT.2020 remains a significant challenge. Here, an effective approach is proposed to design deep-blue TADF molecules based on hybrid long- and short-range charge-transfer by incorporation of multiple donor moieties into organoboron multiple resonance acceptors. The resulting TADF molecule exhibits deep-blue emission at 414 nm with a full width at half maximum (FWHM) of 29 nm, together with a thousand-fold increase in RISC rate. OLEDs based on the champion material achieve a record maximum external quantum efficiency (EQE) of 22.8% with CIE coordinates of (0.163, 0.046), approaching the coordinates of the BT.2020 blue standard. Moreover, TADF-assisted fluorescence devices employing the designed material as a sensitizer exhibit an exceptional EQE of 33.1%. This work thus provides a blueprint for future development of efficient deep-blue TADF emitters, representing an important milestone towards meeting the blue color gamut standard of BT.2020.

Bis(Aluminyl)Magnesium: A Source of Nucleophilic or Radical Aluminium-Centred Reactivity.

The homoleptic magnesium bis(aluminyl) compound Mg[Al(NON)]2 (NON=4,5-bis(2,6-diisopropylanilido)-2,7-di-tert-butyl-9,9-dimethylxanthene) can be accessed from K2[Al(NON)]2 and MgI2 and shown to possess a non-linear geometry (∠Al-Mg-Al=164.8(1)°) primarily due to the influence of dispersion interactions. This compound acts a four-electron reservoir in the reductive de-fluorination of SF6, and reacts thermally with polar substrates such as MeI via nucleophilic attack through aluminium, consistent with the QT-AIM charges calculated for the metal centres, and a formal description as a Al(I)-Mg(II)-Al(I) trimetallic. On the other hand, under photolytic activation, the reaction with 1,5-cyclooctadiene leads to the stereo-selective generation of transannular cycloaddition products consistent with radical based chemistry, emphasizing the covalent nature of the Mg-Al bonds and a description as a Al(II)-Mg(0)-Al(II) synthon. Consistently, photolysis of Mg[Al(NON)]2 in hexane in the absence of COD generates [Al(NON)]2 together with magnesium metal.