Mustafa Tavasli

White polymeric light-emitting diode based on a fluorene polymer∕Ir complex blend system

Efficient white-polymeric light-emitting diodes (PLED) were fabricated as a single active layer containing blue-emitting poly(9,9-bis(2-ethylhexyl)fluorene-2,7-diyl) endcapped with bis(4-methylphenyl)phenylamine; (PF2∕6am4), and yellow-orange-emitting iridium [tri-fluorenyl] pyridine complex [Ir(Fl3Py)3]. The fluorene-like ligands in the blended device prevent phase segregation and also enhance energy transfer from the polymer host to the guest due to efficient overlap of wave function (Dexter process) and host singlet emission and guest absorption bands (Forster process) which reduces the loading level required to produce white emission. The two emitted colors complement each other and doping levels of 2%–3% produce white emission. Above a certain current density, depending on the doping level, the device Commission Internationale de L’Eclairage (CIE) coordinates become bias independent and a stabilized white emission can be obtained. A white-emitting PLED (coordinates 0.348, 0.367) of peak external quan...

Colour tuning from green to red by substituent effects in phosphorescent tris-cyclometalated iridium(III) complexes of carbazole-based ligands: synthetic, photophysical, computational and high efficiency OLED studies

Two series of fac-tris-cyclometalated iridium(III) complexes, series 1 from the 2-(carbazol-3′-yl)-pyridine ligands, and series 2 from the isomeric 2-(carbazol-2′-yl)-pyridine ligands, have been characterised. The photoluminescence and electroluminescence from series 2 complexes are red shifted compared to series 1 complexes, due to the increased electron donating ability of the carbazole unit in series 2. The attachment of trifluoromethyl and methoxy substituents to the pyridyl ring in these complexes results in colour tuning of phosphorescence energy maxima over the range 494–637 nm (green to red). These complexes possess predominantly 3MLCT (metal-to-ligand-charge transfer) excited states. DFT/TD-DFT computations correctly predict the phosphorescence emission maxima and show that the HOMOs in these complexes contain mixed iridium and carbazolyl character. The carbazolyl ligand contributions to the excited states increase in series 2 compared to series 1. Complexes of series 1 exhibit high phosphorescence quantum yields whereas complexes of series 2 show lower quantum yields. Solution processed organic light emitting devices (OLEDs) with series 1 complexes using the high triplet poly(9-vinylcarbazole) (PVK) as the host polymer exhibit very high performances of up to 40 cd A−1 and external quantum efficiency of 12%. For series 2 the highest current efficiency is 10.3 cd A−1 and external quantum efficiency of 5.6%.

A short synthesis of (S)-2-(diphenylmethyl)pyrrolidine, a chiral solvating agent for NMR analysis

Abstract A three step synthesis of (S)-2(diphenylmethyl)pyrrolidine 4 is described which allows its preparation on a large scale. The C2 symmetric diamines 5 and 6 have been prepared from 4 and are attractive as potential ligands for asymmetric transformations. Pyrrolidine 4 has been assessed as a chiral solvating agent for the NMR analysis of chiral compounds. It emerges as a good CSA for carboxylic acids and some secondary alcohols.

Bridged diiridium complexes for electrophosphorescent OLEDs: synthesis, X-ray crystal structures, photophysics, and devices

Results are presented which challenge the accepted view that dinuclear transition metal–ligand complexes are unsuitable for organic light-emitting device (OLED) applications due to their low luminescence quantum efficiencies. We establish for the first time that halo- and pseudo-halo-bridged diiridium(III) species are viable electrophosphorescent dopants in OLEDs. New cyclometalated chloro- and isocyanate-bridged diiridium(III) complexes, viz. tetrakis[9,9-dihexyl-2-(pyridin-2-yl)fluorene-C2,N′]-bis(μ-chloro)diiridium(III) [Ir(flpy)2Cl]2 (complex 3) and tetrakis[9,9-dihexyl-2-(pyridin-2-yl)fluorene-C2,N′]-bis(μ-isocyanate)diiridim(III) [Ir(flpy)2NCO]2 (complex 4) were obtained in high yield from the 9,9-dihexyl-2-(pyridin-2-yl)fluorene (flpyH) ligand 1. The X-ray crystal structures are described for 3 and the monomeric complex Ir(flpy)2NCO(DMSO) (5) which was obtained from 4. The solution-state photophysical properties of complexes 3 and 4 are characterised by emission from mixed 3π–π*/3MLCT states at ∼545–550 nm. Complex 4 displays a solution-state photoluminescence quantum yield which is five times that of the dichloro-bridged analogue 3. This is ascribed to an increase in the ligand-LUMO/metal eg gap which reduces the probability of non-radiative decay processes. Spin-coated organic light emitting devices (OLEDs) made from the host polymer poly(9,9-bis-2-ethylhexylfluorene-2,7-diyl) (PF2/6) end-capped with bis-(4-methylphenyl)phenylamine (PF2/6am4) doped with 12.5 wt% of the complexes 3 and 4 show good stability: turn-on voltages are low (<4 V) with maximum EL intensities of ∼1300 and 13 000 cd m−2, and peak external quantum efficiencies (EQE) of 0.1 and 0.8%, at ca. 400 and 60 mA cm−2, respectively.

Oligo(fluorenyl)pyridine ligands and their tris-cyclometalated iridium(III) complexes: synthesis, photophysical properties and electrophosphorescent devices

The new extended tri- and penta-fluorenylpyridine ligands Fl3Py 2 and Fl5Py 3 and their tris-cyclometalated iridium(III) complexes Ir[Fl3Py]35 and Ir[Fl5Py]36 have been synthesised and their properties compared with the known iridium(III) complex Ir[Fl1Py]34. The lowest energy (emissive) excited states of the complexes 4–6 are dominated by ligand centred (LC) π→π* triplet states, as observed for their uncomplexed ligands 1–3. The emission maximum of complex 4 is ∼546 nm with a triplet lifetime of 2.8 µs. For complexes 5 and 6 the emission maxima are both ∼566 nm with triplet lifetimes of 7.4 µs and 7.8 µs, respectively. Devices made from poly(9,9′-spirobifluorene) (PSF) as the host and doped with complexes 4–6 show good stability; the EL spectra are unchanged after repeated operation over several days. Devices containing complexes 5 and 6 exhibit higher external quantum efficiency (EQE) values. Turn-on voltages of ∼3 V, giving an EQE of 2.8% at a current density of 30 mA cm−2, with a power efficiency of 4.3 lm W−1 and electroluminescence (EL) intensity of 25 000 cd m−2 at 550 mA cm−2 were observed for ITO/PEDOT ∶ PSS/PSF ∶ 6/Ca/Al devices.

Molecular Bridging of Silicon Nanogaps

The highly doped electrodes of a vertical silicon nanogap device have been bridged by a 5.85 nm long molecular wire, which was synthesized in situ by grafting 4-ethynylbenzaldehyde via C-Si links to the top and bottom electrodes and thereafter by coupling an amino-terminated fluorene unit to the aldehyde groups of the activated electrode surfaces. The number of bridging molecules is constrained by relying on surface roughness to match the 5.85 nm length with an electrode gap that is nominally 1 nm wider and may be controlled by varying the reaction time: the device current increases from ≤1 pA at 1 V following the initial grafting step to 10-100 nA at 1 V when reacted for 5-15 min with the amino-terminated linker and 10 μA when reacted for 16-53 h. It is the first time that both ends of a molecular wire have been directly grafted to silicon electrodes, and these molecule-induced changes are reversible. The bridges detach when the device is rinsed with dilute acid solution, which breaks the imine links of the in situ formed wire and causes the current to revert to the subpicoampere leakage value of the 4-ethynylbenzaldehyde-grafted nanogap structure.

A short synthesis of (S)-α-(diphenylmethyl)alkyl amines from amino acids

Abstract A range of ( S )-α-(diphenylmethyl)alkyl amines were prepared from the corresponding ( S )-α-amino acid ester hydrochlorides. These amines were derived by direct hydrogenation of their precursor oxazolidinones.

A synthesis of (S)-α-(fluorodiphenylmethyl)alkylamines by HF–pyridine treatment of 4-alkyl-5,5-diphenyl-oxazolidinones

Abstract Treatment of enantiomerically pure (S)-4-alkyl-5,5-diphenyl-oxazolidinones, themselves derived from appropriate amino acids, with HF–pyridine (Olahs reagent) generated a range of (S)-α-(fluorodiphenylmethyl)alkylamines. These compounds represent a novel range of fluorinated chiral amines.

White polymeric light-emitting diode based on a fluorene polymer/Ir complex blend system

New extended fluorenylpyridine ligands FlnPy (n=1,3,5) and their triscyclometalated iridium (III) complexes Ir[FlnPy]3 3, 4, and 5 have been synthesised and their photophysical properties have been studied. The lowest energy (emissive) excited state of the complexes 3-5 is dominated by ligand centered 3(π→π*) triplet states, as observed in their ligands. Efficient white-polymeric light-emitting diodes (PLED) were fabricated as a single active layer containing blue emitting poly (9,9-bis(2-ethylhexyl)fluorine-2,7- diyl) endcapped with bis(4-methylphenyl)phenylamine (PF2/6am4), and yellow-orange emitting from Iridium complex 4. The fluorene-like ligands in the blended device prevent phase segregation and also enhance energy transfer from the polymer host to the guest due to efficient overlap of wavefunction (Dexter process) and host singlet emission and guest absorption bands (F&diaero;rster process) which reduces the loading level required to produce white emission. The two emitted colours complement each other and doping levels between 2% to 3% produce white emission. Above a certain current density depending on the doping level the device CIE coordinates become bias independent and a stabilised white emission can be obtained. A white emission PLED (coordinate (0. 348, 0.367) of peak external quantum efficiency (EQE) of 2.8 %, and luminance of 16000 cd/m2) at applied voltage of 5V (ie. 4.57 cd/A) was obtained. device CIE coordinates become bias independent and a stabilised white emission can be obtained. A white emission PLED (coordinate (0. 3477, 0.3667) of peak external quantum efficiency (EQE) of 2.8 %, and luminance of 16000 cd/m2 at applied voltage of 5V (ie. 4.57 cd/A) was obtained.

The synthesis, conformation and antimuscarinic properties of ketone analogues of tropane esters

A synthesis of the ketone analogues of three naturally occurring tropane esters has been developed and one of the ketones has been evaluated for its efficacy as a muscarinic acetylcholine receptor (mAChR) antagonist in guinea-pig ileum. The ketone analogue of apoatropine displayed an IC50 value in the micromolar range when compared to atropine, which has antagonist activity in the nanomolar range. The conformational change in replacing the bridging oxygen of the ester moiety by CH2 has been assessed by X-ray structure analysis of one of the compounds and has been evaluated more widely in a Cambridge Crystallographic Database survey. The structural data reveals that both the tropane esters and tropane ketones adopt similar conformations.