Manju Rajeswaran

Non-blinking semiconductor nanocrystals

The photoluminescence from a variety of individual molecules and nanometre-sized crystallites is defined by large intensity fluctuations, known as ‘blinking’, whereby their photoluminescence turns ‘on’ and ‘off’ intermittently, even under continuous photoexcitation. For semiconductor nanocrystals, it was originally proposed that these ‘off’ periods corresponded to a nanocrystal with an extra charge. A charged nanocrystal could have its photoluminescence temporarily quenched owing to the high efficiency of non-radiative (for example, Auger) recombination processes between the extra charge and a subsequently excited electron–hole pair; photoluminescence would resume only after the nanocrystal becomes neutralized again. Despite over a decade of research, completely non-blinking nanocrystals have not been synthesized and an understanding of the blinking phenomenon remains elusive. Here we report ternary core/shell CdZnSe/ZnSe semiconductor nanocrystals that individually exhibit continuous, non-blinking photoluminescence. Unexpectedly, these nanocrystals strongly photoluminesce despite being charged, as indicated by a multi-peaked photoluminescence spectral shape and short lifetime. To model the unusual photoluminescence properties of the CdZnSe/ZnSe nanocrystals, we softened the abrupt confinement potential of a typical core/shell nanocrystal, suggesting that the structure is a radially graded alloy of CdZnSe into ZnSe. As photoluminescence blinking severely limits the usefulness of nanocrystals in applications requiring a continuous output of single photons, these non-blinking nanocrystals may enable substantial advances in fields ranging from single-molecule biological labelling to low-threshold lasers.

Coumarin-Based, Electron-Trapping Iridium Complexes as Highly Efficient and Stable Phosphorescent Emitters for Organic Light-Emitting Diodes

A new class of coumarin-based iridium tris-cyclometalated complexes has been developed. These complexes are highly emissive, with emission colors ranging from green to orange-red. Besides modification of ligand structures, color tuning was realized by incorporation of ligands with different electrochemical properties in a heteroleptic structure. The organic light-emitting diodes (OLEDs) using these compounds as emissive dopants are highly efficient and stable. Unlike other Ir(III) phosphorescent dopants, these coumarin-based Ir(III) dopants can effectively trap and transport electrons in the emissive layer.

p-Phenyl­ene­diammonium tetra­chloro­zincate(II)

# 2006 International Union of Crystallography All rights reserved The structure of the title compound, (C6H10N2)[ZnCl4], contains simple ZnCl4 tetrahedra in the bc plane creating alternating layers of organic and inorganic sublattices, a feature that is very common for compounds of this type. The two sublattices are held together by coulombic attraction of the cationic organic sublattice and anionic inorganic sublattice and also by hydrogen bonding. The anions are located on general positions. The cations, however, are located on mirror planes. As a result, there are two half-cations in the asymmetric unit.

Retraction: Non-blinking semiconductor nanocrystals

This corrects the article DOI: 10.1038/nature08072

Tris­(quinolin-8-olato)­indium(III)

The single-crystal structure of the title compound, [In(C9H6NO)3], is described. Quinolinolates of the elements of the group IIIB (denoted by MQ3), Al, Ga, and In, have been of continuous interest to organometallic and physical chemists, in particular, for the last 50 years. Organic light-emitting diodes (OLEDs) utilizing GaQ3 and InQ3, the gallium and indium analogs, respectively, of the most widely used OLED material AlQ3, were first explored in the early 1980s and continue to be the subject of current research. To the best of our knowledge, the structure reported here is the first-ever facial MQ3-type structure, confirmed by single-crystal X-ray crystallography.

Structure and Conformation of 1-β-D-Ribo Furanosyl Pyridin-2-one-5-Carboxamide: An Anti-Inflammatory Agent

The pyrimidine nucleoside, 1-β-D-ribofuranosyl pyridine-2-one-5-carboxamide, is an anti inflammatory agent used in the treatment of adjuvant-induced arthritis. It is the 2-one isomer of 1-β-D-ribofuranosyl pyridine-4-one 5-carboxamide, an unusual nucleoside isolated from the urine of patients with chronic myelogenic leukemia and an important cancer marker. Crystals of 1-β-D-ribofuranosyl pyridine-2-one-5-carboxamide are monoclinic, space group C2, with the cell dimensions a = 31.7920(13), b = 4.6872 (3), c = 16.1838(11), β = 93.071(3)°, V = 2408.2(2) Å3, Dcalc = 1.496 mg/m3 and Z = 8 (two molecules in the asymmetric unit). The structure was obtained by the application of direct methods to diffractometric data and refined to a final R value of 0.050 for 1669 reflections with I ≥ 3σ. The nucleoside exhibits an anti conformation across the glycosidic bond (χCN = −15.5°, −18.9°), a C3 ′- endo C2 ′ -exo [3 2T] ribose pucker and g+ across the C(4 ′)-C(5 ′) exocyclic bond. The amino group of the carboxamide group is distal from the 2-one and lacks the intramolecular hydrogen bonding found in the related 2-one molecule. Nuclear magnetic resonance studies shows also an anti conformation across the glycosidic bond but the solution conformation of the furanose ring is not the same as that found in the solid state.

N,N'-Dicyclo-hexyl-naphthalene-1,8;4:5-dicarboximide.

The title compound, C26H26N2O4, synthesized by the reaction of naphthalene-1,4,5,8-tetracarboxylic acid anhydride and cyclohexylamine, exhibits good n-type semiconducting properties. Accordingly, thin-film transistor devices comprising this compound show n-type behavior with high field-effect electron moblity ca 6 cm2/Vs [Shukla, Nelson, Freeman, Rajeswaran, Ahearn, Meyer & Carey(2008 ▶). Chem. Mater. Submitted]. The asymmetric unit comprises one-quarter of the centrosymmetric molecule in which all but two methylene C atoms of the cyclohexane ring lie on a mirror plane; the point-group symmetry is 2/m. The naphthalenediimide unit is strictly planar, and the cyclohexane rings adopt chair conformations with the diimide unit in an equatorial position on each ring.

P-178: High-Efficiency Long-Lifetime Phosphorescent OLED Devices Based on Electron-Trapping Iridium (III) Complexes

We have developed new iridium (III) complexes having coumarin, including its aza-analogue structure, in their ligands. These Ir complexes are highly emissive with colors ranging from yellow, yellowish-green to green. Electrochemical analysis shows that the reduction and oxidation potentials of these complexes occur at significantly less negative and more positive potentials, respectively, than are found for typical Ir(III) complexes in OLEDs, indicating these complexes are electron trapping instead of hole trapping. Long-lived phosphorescent OLEDs fabricated with these new Ir complexes give external quantum and power efficiencies above 18% and 33 lm/W, respectively.

catena-Poly[[aqua-1κO-μ2-succinimidato-1:2κ2O:N-disilver(I)]-μ3-succinimidato-1:2:1′κ3O:N:O′]

The structure of the title compound, [Ag2(C4H4NO2)2(H2O)]n, exhibits a butterfly-shaped [Ag(C4H4NO2)]2 dimer which contains an eight-membered ring. One of the Ag atoms is four-coordinate having exclusively Ag—O bonds and the other is two-coordinate having exclusively Ag—N bonds.

Bis(2‐methyl­quinolin‐8‐olato‐κ2N,O)(6‐phenyl‐2‐naphtholato‐κO)aluminium(III)

The five-coordinate geometry of the Al atom in the title compound, [Al(C10H8NO)2(C16H11O)], is trigonal–bipyramidal, in which the O-donor atoms of the naphtholate and the two quinolinolate ligands are in the trigonal equatorial plane and the N atoms in the axial positions.