In situ formation and photo patterning of emissive quantum dots in small organic molecules

Nanostructured composites of inorganic and organic materials are attracting extensive interest for electronic and optoelectronic device applications. Here we report a novel method for the fabrication and patterning of metal selenide nanoparticles in organic semiconductor films that is compatible with solution processable large area device manufacturing. Our approach is based upon the controlled in situ decomposition of a cadmium selenide precursor complex in a film of the electron transporting material 1,3,5-tris(N-phenyl-benzimidazol-2-yl)-benzene (TPBI) by thermal and optical methods. In particular, we show that the photoluminescence quantum yield (PLQY) of the thermally converted CdSe quantum dots (QDs) in the TPBI film is up to 15%. We also show that laser illumination can form the QDs from the precursor. This is an important result as it enables direct laser patterning (DLP) of the QDs. DLP was performed on these nanocomposites using a picosecond laser. Confocal microscopy shows the formation of emissive QDs after laser irradiation. The optical and structural properties of the QDs were also analysed by means of UV-Vis, PL spectroscopy and transmission electron microscopy (TEM). The results show that the QDs are well distributed across the film and their emission can be tuned over a wide range by varying the temperature or irradiated laser power on the blend films. Our findings provide a route to the low cost patterning of hybrid electroluminescent devices

Solubilised bright blue-emitting iridium complexes for solution processed OLEDs

EZ-C acknowledges the University of St Andrews for financial support. IDWS and AKB acknowledge support from EPSRC (EP/J01771X). The authors would like to thank the Engineering and Physical Sciences Research Council for financial support for Adam Henwood: EPSRC DTG Grants: EP/J500549/1; EP/K503162/1; EP/L505097/1.Combining a sterically bulky, electron-deficient 2-(2,4-difluorophenyl)-4-(2,4,6- trimethylphenyl)pyridine (dFMesppy) cyclometalating C^N ligand with an electron rich, highly rigidified 1,1’-(α,α’-o-xylylene)-2,2’-biimidazole (o-xylbiim) N^N ligand gives an iridium complex, [Ir(dFMesppy)2(o-Xylbiim)](PF6), that achieves extraordinarily bright blue emission (ΦPL = 90%; λmax = 459 nm in MeCN) for a cationic iridium complex. This complex is compared with two reference complexes bearing 4,4’-di-tert-butyl-2,2’- bipyridine, and solution-processed organic light emitting diodes (OLEDs) have been fabricated from these materials.Publisher PDFPeer reviewe

pH-Induced transformation of ligated Au 25 to brighter Au 23 nanoclusters

Thiolate-protected gold nanoclusters have recently attracted considerable attention due to their size-dependent luminescence characterized by a long lifetime and large Stokes shift. However, the optimization of nanocluster properties such as the luminescence quantum yield is still a challenge. We report here the transformation of Au25Capt18 (Capt labels captopril) nanoclusters occurring at low pH and yielding a product with a much increased luminescence quantum yield which we have identified as Au23Capt17. We applied a simple method of treatment with HCl to accomplish this transformation and we characterized the absorption and emission of the newly created ligated nanoclusters as well as their morphology. Based on DFT calculations we show which Au nanocluster size transformations can lead to highly luminescent species such as Au23Capt17

Tuning the exciton diffusion coefficient of polyfluorene based semiconducting polymers

The authors acknowledge financial support from FP7 project “Laser Induced Synthesis of Polymeric Nanocomposite Materials and Development of Micro‐patterned Hybrid Light Emitting Diodes (LED) and Transistors (LET)” – LAMP project (G.A. 247928). M.T.S., A.R., and I.D.W.S. acknowledge support from the European Research Council (EXCITON grant 321305). I.D.W.S. acknowledges a Royal Society Wolfson Research Merit Award. The authors are grateful to EPSRC for an equipment grant (EP/L017008/1).Exciton diffusion plays an important role in functional materials used in organic optoelectronic devices, such as solar cells, organic light emitting diodes, and lasers. Here we explore how exciton diffusion can be controlled in highly fluorescent blue‐emitting polyfluorene materials by changing the length and type of side chains. We find that the exciton diffusion coefficient (D) decreases from 1.2 × 10−3 cm2 s−1 to 0.2×10−3 cm2 s−1 when the side chain length is increased from 8 to 12 carbon atoms. Other changes to the side chains led to enhancement of D up to 1.6 × 10−3 cm2 s−1. Our results show that small adjustments to the molecular structure can be helpful for the future development of high‐brightness organic light emitting devices.PostprintPostprintPeer reviewe

Wearable organic optoelectronic sensors for medicine

This work was supported by Engineering and Physical Sciences Research Council Programme Grant “Challenging the limits of photonics: Structured light” (grant number EP/J01771X/1) and MRC.Organic optoelectronic devices that can be used to make compact, wearable sensors for medicine and sports are shown and two examples are given: a tissue-oxygenation sensor and a muscle-contraction sensor. It is demonstrated how the muscle-contraction sensor on a volunteer's arm can successfully control the robot arm.Publisher PDFPeer reviewe

Comparison of hole mobility in thick and thin films of a conjugated polymer

The problem that conventional time of flight (TOF) mobility measurements are made on much thicker films than typically used in organic optoelectronic devices is investigated by comparing the mobility of thick and thin films of the poly(phenylenevinylene) based copolymer "SuperYellow". We report for the first time mobility values perpendicular to the substrate for this widely used material and find them to be of the order of 10(-6)-10(-7) cm(2)/V s for both spin-coated and drop-cast films. A high photoluminescence quantum yield (PLQY) of 60 +/- 5% is measured for both types of films. The results indicate a trade-off between PLQY and charge transport in poly(arylenevinylene) s. The insensitivity of the charge transporting and photophysical properties to the film preparation procedure and thickness is a desirable characteristic that may result from the bulky side groups of "SuperYellow". (C) 2009 Elsevier B.V. All rights reserved.</p

Palladium(0) NHC complexes : a new avenue to highly efficient phosphorescence

We report the first examples of highly luminescent di-coordinated Pd(0) complexes. Five complexes of the form [Pd(L)(L’)] were synthesized, where L = IPr, SIPr or IPr* NHC ligands and L’ = PCy3, or IPr and SIPr NHC ligands. The photophysical properties of these complexes were determined in toluene solution and in solid state and contrasted to the poorly luminescent reference complex [Pd(IPr)(PPh3)]. Organic light-emitting diodes were successfully fabricated but attained external quantum efficiencies of between 0.3 and 0.7%