One-Shot Synthesis of Expanded Heterohelicene Exhibiting Narrowband Thermally Activated Delayed Fluorescence.

An expanded heterohelicene consisting of three BN2-embedded [4]helicene subunits (V-DABNA-Mes) has been synthesized by one-shot triple borylation. The key to success is the excessive use of boron tribromide in an autoclave. Based on the multiple resonance effect of three boron and six nitrogen atoms, V-DABNA-Mes exhibited a narrowband sky-blue thermally activated delayed fluorescence with a full width at half-maximum of 16 nm. The resonating π-extension minimized the singlet-triplet energy gap and enabled rapid reverse intersystem crossing with a rate constant of 4.4 × 105 s-1. The solution-processed organic light-emitting diode device, employed as an emitter, exhibited a narrowband emission at 480 nm with a high external quantum efficiency of 22.9%.

Solution-Processable Pure Green Thermally Activated Delayed Fluorescence Emitter Based on the Multiple Resonance Effect.

Thermally activated delayed fluorescence (TADF) materials based on the multiple resonance (MR) effect are applied in organic light-emitting diodes (OLEDs), combining high color purity and efficiency. However, they are not fabricated via solution-processing, which is an economical approach toward the mass production of OLED displays. Here, a solution-processable MR-TADF material (OAB-ABP-1), with an extended π-skeleton and bulky substituents, is designed. OAB-ABP-1 is synthesized from commercially available starting materials via a four-step process involving one-shot double borylation. OAB-ABP-1 presents attractive photophysical properties, a narrow emission band, a high photoluminescence quantum yield, a small energy gap between S1 and T1 , and low activation energy for reverse intersystem crossing. These properties are attributed to the alternating localization of the highest occupied and lowest unoccupied molecular orbitals induced by the boron, nitrogen, and oxygen atoms. Furthermore, to facilitate charge recombination, two novel semiconducting polymers with similar ionization potentials to that of OAB-ABP-1 are synthesized for use as interlayer and emissive layer materials. A solution-processed OLED device is fabricated using OAB-ABP-1 and the aforementioned polymers; it exhibits pure green electroluminescence with a small full-width at half-maximum and a high external quantum efficiency with minimum efficiency roll-off.

Hydrogen-bonding-assisted self-doping in tetrathiafulvalene (TTF) conductor.

The synthesis, characterization, and carrier generation mechanism of self-doping in a tetrathiafulvalene (TTF) conductor, ammonium tetrathiafulvalene-2-carboxylate (TTFCOO(-)NH(4)(+)), are described together with molecular orbital characteristics. Insulating TTFCOOH changes into a hole-doped conductor TTFCOO(-)NH(4)(+) with a conductivity of sigma = 2.0 x 10(-4) S/cm (300 K), upon salt formation with NH(3). A radical species, TTF(*+)COO(-)NH(4)(+), is generated via protonation of the TTF moiety as demonstrated by UV-vis, ESR, and (1)H NMR spectra. The X-ray crystallographic structure of TTFCOO(-)NH(4)(+) reveals supramolecular arrays of TTFCOO(-) moieties with short S...S contact, assisted by the one-dimensional hydrogen-bonding network composed of the ammonium and carboxylate ions. Molecular orbital calculations of cluster models show that the singly occupied molecular orbital (SOMO) of TTF(*+)COO(-)NH(4)(+) in the supramolecular array is not at the highest energy level, which is characterized as a quasi-closed-shell state. The ab initio periodic calculation with a one-dimensional boundary condition reveals that TTF(*+)COO(-)NH(4)(+) behaves as a dopant leading to the semiconducting behavior of the stacked TTF moieties assembled by the hydrogen-bonding network. Namely, TTFCOO(-)NH(4)(+) can be described as a "hydrogen-bonding-assisted self-doped conductor". The contribution of the hydrogen-bonding interaction to the electron conduction is experimentally supported by a large isotope effect in the ac conductivity of TTFCOO(-)NH(4)(+) at low temperature.