James M. Macdonald

Highly Efficient Organic Light‐Emitting Diode Based on a Hidden Thermally Activated Delayed Fluorescence Channel in a Heptazine Derivative

An orange-red organic light-emitting diode containing a heptazine derivative exhibits high performance with a maximum external quantum efficiency of 17.5 ± 1.3% and a peak luminance of 17000 ± 1600 cd m⁻² without any light out-coupling enhancement. The high electroluminescence performance can be ascribed to the presence of an efficient up-conversion channel from the lowest triplet state to the lowest singlet state.

Hierarchical self-assembly of semiconductor functionalized peptide α-helices and optoelectronic properties.

To determine the ability of semiconductors templated by α-helical polypeptides to form higher order structures and the charge carrier properties of the supramolecular assemblies, L-lysine was functionalized with a sexithiophene organic semiconductor unit via iterative Suzuki coupling and the click reaction. The resultant amino acid was incorporated into a homopolypeptide by ring-opening polymerization of an amino acid N-carboxyanhydride. Spectroscopic investigation of the polypeptide revealed that it adopted an α-helical secondary structure in organic solvents that underwent hierarchical self-assembly to form higher order structures. In cyclohexane, the polymer formed organogels at 2% (w/v). Organic photovoltaic and organic field effect transistor devices were fabricated by deposition of the PCBM blended active layer from chlorobenzene at concentrations shown to induce self-assembly of the polymer. Compared with control compounds, these devices showed significantly greater hole mobility, short circuit current, and efficiency. This work establishes the potential of this previously unreported bioinspired motif to increase device performance.

A gram-scale batch and flow total synthesis of perhydrohistrionicotoxin.

The total synthesis of the spiropiperidine alkaloid (-)-perhydrohistrionicotoxin (perhydro-HTX) 2 has been accomplished on a gram scale by employing both conventional batch chemistry as well as microreactor techniques. (S)-(-)-6-Pentyltetrahydro-pyran-2-one 8 underwent nucleophilic ring opening to afford the alcohol 10, which was elaborated to the nitrone 13. Protection of the nitrone as the 1,3-adduct of styrene and side-chain extension to the unsaturated nitrile afforded a precursor 17, which underwent dipolar cycloreversion and 1,3-dipolar cycloaddition to give the core spirocyclic precursor 18 that was converted into perhydro-HTX 2. The principal steps to the spirocycle 18 have successfully been transferred into flow mode by using different types of microreactors and in a telescoped fashion, allowing for a more rapid access to the histrionicotoxins and their analogues by continuous processing.

Total Synthesis of (−)-Histrionicotoxin 285A and (−)-Perhydrohistrionicotoxin

Starting from commercially available ( S)-glycidol, and via a common intermediate, the total synthesis of (-)-histrionicotoxin 285A and (-)-perhydrohistrionicotoxin has been achieved. Key to this synthesis was the efficient construction of a six-membered, chiral, cyclic nitrone.

New blue phosphorescent iridium complexes for OLEDs

— A new class of ligands for complexation with Ir(III) has been developed. Tris-homoleptic complexes derived from these ligands have been found to exhibit highly efficient blue phosphorescence with photoluminescent quantum yields in solution at room temperature of >0.9. These complexes have been applied as the emissive materials in OLEDs to give devices with efficiencies of up to 26 cd/A and an E.Q.E. of 1 7.4% at 1 mA/cm2.

N-Tetrahydrothiochromenoisoxazole-1-carboxamides as selective antagonists of cloned human 5-HT2B

The serendipitous discovery of N-cyclohexyl-8-fluoro-3,3a,4,9b-tetrahydro-1H-thiochromeno[4,3-c]isoxazole-1-carboxamide as a selective human serotonin 5-HT2B antagonist with Ki of 42+/-5 nM is reported herein. A subsequent functional assay indicated little agonist activity compared to 5-HT itself.

Highly Efficient Organic Light-Emitting Diode Based on a Hidden Thermally Activated Delayed Fluorescence Channel in a Heptazine Derivative

Considerable progress in organic light-emitting diodes (OLEDs) has triggered intensive effort to develop efficient solid-state electroluminescent (EL) materials over the past two decades. Among the many classes of materials being investigated, transition metal complexes are highly attractive because phosphorescent OLEDs containing Ir (III), Pt (II) and Os (II) complexes exhibit very high external quantum efficiencies (ηext). This is because such complexes effectively harvest triplet excitons, so their efficiencies are four times higher than that of conventional fluorescent OLEDs. However, phosphorescent OLEDs containing transition metal-based compounds are rather expensive and unsustainable because they contain rare metals. While OLEDs containing Cu (I) complexes that exhibit high ηext comparable to those with transition metal complexes have been examined as an alternative, the relatively low reliability and high driving voltage of such OLED are fundamental problems. Therefore, a novel way to realize high EL efficiency is required. Although fluorescent OLEDs have been assumed to show limited efficiency because of the branching ratio of singlet and triplet excitons of 1:3, the most recent fluorescence-based OLEDs have overcome this limitation using triplet-triplet annihilation and thermally activated delayed fluorescence (TADF) [1-2]. In particular, we have developed promising blue and green TADF materials [3-4]. However, the design of efficient orange or red emitters is inherently difficult because the photoluminescence (PL) quantum efficiency tends to decrease as the emission wavelength increases according to the energy gap law.

P‐165: A New Class of Blue Phosphorescent Iridium Complexes for Organic Electroluminescent Devices

We report a new class of phosphorescent Ir(III) complexes that exhibit highly efficient blue emission. These complexes display an absolute quantum yield of greater than 0.9 in solution at room temperature and have been applied in OLED devices that give an efficiency of 15.7 cd/A at 1000 cd/m2 with CIE coordinates of (0.15, 0.21).