Peter J. Skabara

Star-shaped π-conjugated oligomers and their applications in organic electronics and photonics

Strategies for the design and construction of non-linear, 2D and 3D conjugated macromolecules are presented in this critical review. The materials, termed here as star-shaped structures, feature a core unit which may or may not provide conjugated links between arms that radiate like spokes from a central axle. The arms of the macromolecules consist of linear oligomers or irregular conjugated chains lacking a formal repeat unit. The cores range from simple atoms to single or fused aromatic units and can provide a high level of symmetry to the overall structure. The physical properties of the star-shaped materials can be markedly different to their simple, linear conjugated analogues. These differences are highlighted and we report on anomalies in absorption/emission characteristics, electronic energy levels, thermal properties and morphology of thin films. We provide numerous examples for the application of star-shaped conjugated macromolecules in organic semiconductor devices; a comparison of their device performance with those comprising analogous linear systems provides clear evidence that the star-shaped compounds are an important class of material in organic electronics. Moreover, these structures are monodisperse, well-defined, discrete molecules with 100% synthetic reproducibility, and possess high purity and excellent solubility in common organic solvents. They feature many of the attributes of plastic materials (good film-forming properties, thermal stability, flexibility) and are therefore extremely attractive alternatives to conjugated polymers (210 references).

Synthesis and characterization of CdS quantum dots in polystyrene microbeads

Polystyrene microbeads doped with highly luminescent CdS quantum dots (QDs) have been prepared. Polystyrene particles with diameters ranging from 100 nm to 500 µm were prepared by a suspension polymerization method and with different loadings of QDs. The resulting organic–inorganic microspheres have been characterized by FTIR, elemental analysis and SEM. Confocal microscopy and photoluminescence studies proved that the CdS nanoparticles were evenly distributed throughout the polystyrene spheres. The QD-containing composites have similar optical properties to isolated CdS QDs. The thermal decomposition of the hybrid materials occurred at higher temperature than for the parent organic materials.

Low-threshold organic laser based on an oligofluorene truxene with low optical losses

A blue-emitting distributed feedback laser based on a star-shaped oligofluorene truxene molecule is presented. The gain, loss, refractive index, and (lack of) anisotropy are measured by amplified spontaneous emission and variable-angle ellipsometry. The waveguide losses are very low for an organic semiconductor gain medium, particularly for a neat film. The results suggest that truxenes are promising for reducing loss, a key parameter in the operation of organic semiconductor lasers. Distributed feedback lasers fabricated from solution by spin-coating show a low lasing threshold of 270 W/cm2 and broad tunability across 25 nm in the blue part of the spectrum.

Nanoimprinted Organic Semiconductor Laser Pumped by a Light‐Emitting Diode

An organic semiconductor laser, simply fabricated by UV-nanoimprint lithography (UV-NIL), that is pumped with a pulsed InGaN LED is demonstrated. Molecular weight optimization of the polymer gain medium on a nanoimprinted polymer distributed feedback resonator enables the lowest reported UV-NIL laser threshold density of 770 W cm(-2) , establishing the potential for scalable organic laser fabrication compatible with mass-produced LEDs.

The synthesis, X-ray structures and CVD studies of some group 11 complexes of iminobis(diisopropylphosphine selenides) and their use in the deposition of I/III/VI photovoltaic materials

Reaction of NH(PiPr2)2 with elemental selenium in concentrated solvent conditions enables large scale preparation and improved yields of NH(PSeiPr2)2 that may be deprotonated with sodium methoxide to give NaN(PSeiPr2)2. Treatment of the sodium salt with appropriate Group 11 metal salts in methanol yields a range of trinuclear complexes. The protic solvent conditions utilized facilitate the reduction of copper(II) salts resulting in the isolation of copper(I) complexes. These new Group 11 complexes have been characterised by 1H and 31P NMR and IR spectroscopy, APCI mass spectrometry, microanalysis and X-ray crystallography. Thermolytic decomposition of the copper(I) precursors in the presence of the indium precursor, In[(SePiPr2)2N]2Cl, has been carried in the solid state using AA-MOCVD to give copper indium diselenide solid state materials CuInSe2.

Linearly extended tetrathiafulvalene analogues with fused thiophene units as π-conjugated spacers

A new series of linearly extended tetrathiafulvalene analogues with thienothiophene and dithienothiophene π-conjugating spacers has been synthesized. Electronic absorption spectra present a vibronic fine structure typical for rigid conjugated systems. Investigation of the electrochemical behaviour of the new donors by cyclic voltammetry reveals the successive generation of stable radical cation and dication species. The crystallographic structure of a single crystal of a dication salt of TT-TTF(ClO4)2 has been analysed by X-ray diffraction. The dication presents a syn conformation stabilised by S⋯S intramolecular interactions. The quinoid structure expected for the spacer for the +2 oxidation state is clearly revealed by the bond lengths.

An Organic Down‐Converting Material for White‐Light Emission from Hybrid LEDs

A novel BODIPY-containing organic small molecule is synthesized and employed as a down-converting layer on a commercial blue light-emitting diode (LED). The resulting hybrid device demonstrates white-light emission under low-current operation, with color coordinates of (0.34, 0.31) and an efficacy of 13.6 lm/W; four times greater than the parent blue LED.

Conducting nanofibers and organogels derived from the self-assembly of tetrathiafulvalene-appended dipeptides

We demonstrate the nonaqueous self-assembly of a low-molecular-mass organic gelator based on an electroactive p-type tetrathiafulvalene (TTF)-dipeptide bioconjugate. We show that a TTF moiety appended with diphenylalanine amide derivative (TTF-FF-NH2) self-assembles into one-dimensional nanofibers that further lead to the formation of self-supporting organogels in chloroform and ethyl acetate. Upon doping of the gels with electron acceptors (TCNQ/iodine vapor), stable two-component charge transfer gels are produced in chloroform and ethyl acetate. These gels are characterized by various spectroscopy (UV-vis-NIR, FTIR, and CD), microscopy (AFM and TEM), rheology, and cyclic voltammetry techniques. Furthermore, conductivity measurements performed on TTF-FF-NH2 xerogel nanofiber networks formed between gold electrodes on a glass surface indicate that these nanofibers show a remarkable enhancement in the conductivity after doping with TCNQ.

Flexible blue-emitting encapsulated organic semiconductor DFB laser.

Mechanically flexible distributed feedback (DFB) lasers are fabricated by a low-cost approach using soft-lithography from a holographic master grating. The gain material is a star-shaped oligofluorene providing laser emission from 425 to 442 nm with a soft pump threshold at 14.4 μJ/cm (2.7 kW/cm). Encapsulation of the devices enables stable operation in ambient atmosphere at a 1/e degradation energy dosage of 53 J/cm.

Conjugated Microporous Networks on the Basis of 2,3,5,6‐Tetraarylated Diketopyrrolo[3,4‐c]pyrrole

π-Conjugated microporous networks have been prepared from the tetraarylated diketopyrrolo[3,4-c]pyrrole unit as a tetrafunctional building block. The reactions are carried out using microwave-assisted Yamamoto or Sonogashira cross-coupling. Red insoluble powders are obtained, showing intense fluorescence. The polymer networks exhibit a high gas storage capability, with BET surface areas up to about 500 m2 · g−1.