ABSTRACT
New BN-heterocyclic compounds have been found to undergo double arene photoelimination, forming rare yellow fluorescent BN-pyrenes that contain two BN units. Most significant is the discovery that the double arene elimination can also be driven by excitons generated electrically within electroluminescent (EL) devices, enabling the in situ solid-state conversion of BN-heterocycles to BN-pyrenes and the use of BN-pyrenes as emitters for EL devices. The inâ situ exciton-driven elimination (EDE) phenomenon has also been observed for other BN-heterocycles.
ABSTRACT
An exciton-stimulated molecular transformation in an organic light-emitting diode (OLED) on a time scale of a few seconds under electrical bias is shown to reach nearly 100% under standard operating conditions, leading to color switching. It is reversible in both a thin film and an OLED when sufficient thermal energy is supplied. Such an exciton-stimulated molecular transformation suggests a new process which may be exploited for applications such as electrochromic and memory devices.
ABSTRACT
The synthesis of highly luminescent, colloidally-stable and organically-capped silicon nanocrystals (ncSi) and their incorporation into a visible wavelength organic light-emitting diode (OLED) is reported. By substituting decyl chains with aromatic allylbenzene capping ligands and size-selecting visible emitting ncSi, superior packing density, enhanced charge transport, and an improved photoluminescence absolute quantum yield of the ncSi is obtained in the active layer of an OLED.
ABSTRACT
The first examples of BMes(2)-functionalized NHC chelate ligands have been achieved. Their Pt(II) acetylacetonate complexes have been synthesized and fully characterized. These NHC-chelate Pt(II) compounds display highly efficient blue or blue-green phosphorescence in solution (Φ = 0.41-0.87) and the solid state (Φ = 0.86-0.90). Highly efficient electroluminescent devices based on these new Pt(II) compounds have also been fabricated.
ABSTRACT
New phosphorescent Pt(II) compounds based on dimesitylboron (BMes(2))-functionalized 2-phenylpyridyl (ppy) N,C-chelate ligands and an acetylacetonato ancillary ligand have been achieved. We have found that BMes(2) substitution at the 4'-position of the phenyl ring can blue-shift the phosphorescent emission energy of the Pt(II) compound by approximately 50 nm, compared to the 5'-BMes(2) substituted analogue, without substantial loss of luminescent quantum efficiencies. The emission color of the 4'-BMes(2) substituted Pt(II) compound, Pt(Bppy)(acac) (1) can be further tuned by the introduction of a substituent group at the 3'-position of the phenyl ring. A methyl substituent red-shifts the emission energy of 1 by approximately 10 nm whereas a fluoro substituent blue-shifts the emission energy by about 6 nm. Using this strategy, three bright blue-green phosphorescent Pt(II) compounds 1, 2 and 3 with emission energy at 481, 492, and 475 nm and Φ(PL)=0.43, 0.26 and 0.25, respectively, have been achieved. In addition, we have examined the impact of BMes(2) substitution on 3,5-dipyridylbenzene (dpb) N,C,N-chelate Pt(II) compounds by synthesizing compound 4, Pt(Bdpb)Cl, which has a BMes(2) group at the 4'-position of the benzene ring. Compound 4 has a phosphorescent emission band at 485 nm and Φ(PL)=0.70. Highly efficient blue-green electroluminescent (EL) devices with a double-layer structure and compounds 1, 3 or 4 as the phosphorescent dopant have been fabricated. At 100 cd m(-2) luminance, EL devices based on 1, 3 and 4 with an external quantum efficiency of 4.7, 6.5 and 13.4%, respectively, have been achieved.
ABSTRACT
We have performed a detailed investigation of the molecular beam epitaxial growth and characterization of InN nanowires spontaneously formed on Si(111) substrates under nitrogen rich conditions. By employing an in situ deposited thin (approximately 0.5 nm) In seeding layer prior to growth initiation, we have achieved, for the first time, non-tapered epitaxial InN nanowires, which exhibit record narrow spectral linewidths of 14 and 40 meV at 5 K and 300 K, respectively. Detailed studies confirm that the wires are nearly free of dislocations and stacking faults. The achievement of non-tapered, nearly homogeneous InN nanowires also enables, for the first time, the derivation of the band gap of InN directly from PL spectroscopy in the temperature range of 5-300 K.
