Browsing by Author "Laskar, IR"

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Electrochemiluminescence studies of the cyclometalated iridium(III) complexes with substituted 2-phenylbenzothiazole ligands
(2004-08-01)
Kapturkiewicz, A
;
Chen, TM
;
Laskar, IR
;
Nowacki, J
;
應用化學系
Electrogenerated chemiluminescence (ECL) studies have been performed for the iridium(III) cyclometalated L2Ir(acac) complexes with substituted 2-phenylbenzothiazole ligand L. Electron transfer (ET) generation of the excited (3)*L2Ir(acac) has been studied using a triple-potential-step technique in acetonitrile-dioxane (1:1) solutions containing 0.1 M (n-C4H9)(4)NPF6 as the supporting electrolyte. ET reactions between electrochemically generated L2Ir(acac)(+) and A(-) (radical anions of aromatic nitriles) species lead to very efficient generation of ECL emission. Extremely high ECL efficiencies (up to 0.40) close to the excited (3)*L2Ir(acac) luminescence yields have been found. (C) 2004 Elsevier B.V. All rights reserved.
Enhanced phosphorescence and electroluminescence in triplet emitters by doping gold into cadmium selenide/zinc sulfide nanoparticles
(2005-10-01)
Liu, HW
;
Laskar, IR
;
Huang, CP
;
Cheng, JA
;
Cheng, SS
Gold-cadmium selenide/zinc sulfide (Au-CdSe/ZnS) nanocomposites (NCs) were synthesized and characterized by transmission electron microscopy (TEM), energy dispersive X-ray (EDX) analysis, ultraviolet-visible (UV-visible) absorption and photoluminescence (PL) emission spectroscopy. The PL intensity in the Au-CdSe/ZnS NCs system was found to be much greater than that of CdSe/ZnS nanoparticles (NPs) alone, because of the surface-enhanced Raman scattering of An NPs. Adding Au-CdSe/ZnS NCs to the cyclometalated iridium(Ill) complex (Ir-complex) greatly enhanced the PL intensity of a triplet emitter. Three double-layered electroluminescence (EL) devices were fabricated where the emitting zone contains the definite mixture of Ir-complex and the NCs [molar concentration of Ir-complex/NCs = 1:0 (Blank, D-1), 1: 1 (D-2) and 1:3 (D-3)] and the device D-2 exhibited optimal EL performances. (c) 2005 Elsevier B.V. All rights reserved.
Highly efficient orange-emitting OLEDs based on phosphorescent platinum(II) complexes
(2005-06-02)
Laskar, IR
;
Hsu, SF
;
Chen, TM
;
應用化學系
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Department of Applied Chemistry
The syntheses, characterisations, photophysical properties and their applications in organic light emitting devices of a series of 2-phenylbenzothiazolato (bt)/substituted 2-phenylbenzothiazolato (X-bt) platinum(II) based square-planar complexes [(X-bt)Pt(acac); acac = acetylacetonate; X = unsubstituted (1), F (2), OMe (3) and CF3 (4)] are discussed. Reaction of K2PtCl4 with btH/X-btH in glacial acetic acid for a few days results in the dinuclear chloro-bridged Pt(II) complex, (bt/X-bt)Pt(mu-Cl)Pt(bt/X-bt) which is cleaved with acetylacetone to give the corresponding mononuclear (bt/X-bt)Pt(acac) complex. The (MeO-bt)Pt(acac) complex has been characterized by X-ray single crystal structure analysis. The packing diagram shows the Pt-Pt distances and the intermolecular spacings are 3.369 and 3.360 angstrom, respectively, which is consistent with excimer formation. It has also been supported by time-resolved photoluminescence (PL) measurements. The nature of the lowest emitting states are the triplet MLCT as well as triplet pi-pi* states and it has been tuned according to the electronic properties of the substituents. The electroluminescent (EL) devices were fabricated by doping platinum complexes 1 and 2 (the corresponding devices denoted as D-1 and D-2, respectively) into the host CBP (4,4'(N,N'-dicarbazole)biphenyl), in the emitting zone with a doping content of 5%, 7% and 9%. The EL performances for these devices are exceptionally high (14.3 and 16.0 cd A(-1) @2 mA cm(-2) and luminances 10 550 and 11320 cd m(-2) @100mA cm(-2) for D-1 and D-2, respectively). (C) 2005 Elsevier Ltd. All rights reserved.
Investigating photoluminescence and electroluminescence of iridium(III)-based blue-emitting phosphors
(2006-03-27)
Laskar, IR
;
Hsu, SF
;
Chen, TM
;
應用化學系
;
Department of Applied Chemistry
The syntheses of two new cyclometalated ligands [2-(2',4'-difluorophenyl)-4-tert-butylpyridine (F(2)(t)Buppy) and 2-(2',4'-difluorophenyl)-4-oxyhexylpyridine (F(2)HexOppy)] were carried out. Blue-light emitting iridium(III) complex dopants [Ir(F(2)Buppy)(2)(acac/pic)] (acac = acetylacetone; pic = picolinic acid) and [Ir(F(2)HeXOppy)(2)(acac/pic)] were prepared using these cyclometalated ligands with acetylacetone and picolinic acid as their ancillary ligands. The structure of the complexes, [Ir(F(2)(t)Buppy)(2)(acac)] and [Ir(F(2)(t)Buppy)(2)(pic)] were authenticated by X-ray single-crystal structure analysis and showed an octahedral geometry. Comparative absorption and emission spectra of thin-films as well as their solution samples were studied. The variation of the lowest emitting states to their corresponding unsubstituted complexes, [Ir(F(2)ppy)(2)(acac/pic)] was also discussed. The electroluminescent (EL) device was fabricated using [Ir(F(2)(t)Buppy)(2)(pic)] as the dopant (D-I) into the emitting layer and compared with two other EL devices where [Ir(F(2)MeOppy)(2)(acac)] (D-II) and FIrpic (D-III) dopants were used in the same device structure. The lower driving voltages obtained for D-I with respect to D-II and D-III devices were rationalized. The exceptional lowering of the luminance yield of the substituted dopants containing devices, D-I and D-II, to that of D-III which contains the unsubstituted dopant was also investigated. (c) 2005 Elsevier Ltd. All rights reserved.
Observing enhanced phosphorescence and electroluminescence from triplet emitter by quantum dot doping
(2005)
Laskar, IR
;
Liu, HW
;
Huang, CP
;
Cheng, JA
;
Chen, TM
Luminescent CdSe/ZnS core-shell-type quantum dots (QDs) were synthesized by chemical colloidal methods. The photoluminescence (PL) intensity of a triplet emitter [bis(4-trifluoromethyl)-2-phenylbenzothiazolatoacetylacetonate-iridium(III) (Ir complex 1) and bis(4-methyl)-2-phenylbenzothiazolatoacetylacetonate-iridium(III) (Ir-complex 2)] was dramatically enhanced when bluish-green emitting CdSe/ZnS QDs were incorporated into these compounds. Experimental results indicate that the emissive region of QDs substantially overlaps with the low-energy absorption bands of Ir-complexes, indicating that the photons were absorbed by both the QDs and the Ir-complexes and that the energy absorbed by the QDs was transferred efficiently to the Ir-complex triplet emitter, resulting in the observed enhancement of PL intensity. A slow quenching of QDs emission was observed in a prepared set of solutions with gradual increasing of Ir complex concentration at a fixed QDs concentration in thin film PMMA matrix, which supports the energy transfer from Ir complex to QDs. In the fabricated double-layer electroluminescent (EL) devices, the emitting layer contained either only Ir-complex or a mixture of Ir-complex and CdSe/ZnS QDs with a specific molar ratio [Ir-complex/QDs = 1/0 (D-I); 1/0.5 (D-II),..., 1/10 (D-V)]. The EL intensity and the luminance efficiency for D-II were higher (luminescence yield = 19.3cd A(-1)) than those of the other devices. The PL and EL enhancement of the triplet emitter were also strongly supported by using ZnSe QDs rather than CdSe/ZnS QDs.
Observing enhanced phosphorescence and electroluminescence from triplet emitter by quantum dot doping
(2005-01-01)
Laskar, IR
;
Liu, HW
;
Huang, CP
;
Cheng, JA
;
Chen, TM
Luminescent CdSe/ZnS core-shell-type quantum dots (QDs) were synthesized by chemical colloidal methods. The photoluminescence (PL) intensity of a triplet emitter [bis(4-trifluoromethyl)-2-phenylbenzothiazolatoacetylacetonate-iridium(III) (Ir complex 1) and bis(4-methyl)-2-phenylbenzothiazolatoacetylacetonate-iridium(III) (Ir-complex 2)] was dramatically enhanced when bluish-green emitting CdSe/ZnS QDs were incorporated into these compounds. Experimental results indicate that the emissive region of QDs substantially overlaps with the low-energy absorption bands of Ir-complexes, indicating that the photons were absorbed by both the QDs and the Ir-complexes and that the energy absorbed by the QDs was transferred efficiently to the Ir-complex triplet emitter, resulting in the observed enhancement of PL intensity. A slow quenching of QDs emission was observed in a prepared set of solutions with gradual increasing of Ir complex concentration at a fixed QDs concentration in thin film PMMA matrix, which supports the energy transfer from Ir complex to QDs. In the fabricated double-layer electroluminescent (EL) devices, the emitting layer contained either only Ir-complex or a mixture of Ir-complex and CdSe/ZnS QDs with a specific molar ratio [Ir-complex/QDs = 1/0 (D-I); 1/0.5 (D-II),..., 1/10 (D-V)]. The EL intensity and the luminance efficiency for D-II were higher (luminescence yield = 19.3cd A(-1)) than those of the other devices. The PL and EL enhancement of the triplet emitter were also strongly supported by using ZnSe QDs rather than CdSe/ZnS QDs.
Syntheses, photoluminescence and electroluminescence of some new blue-emitting phosphorescent iridium(III)-based materials
(2005-01-27)
Laskar, IR
;
Hsu, SF
;
Chen, TM
;
應用化學系
;
Department of Applied Chemistry
The cyclometallated ligand 2-(4',6-difluorophenyl)-4-methoxypyridine (F(2)MeOppyH), whose complexes with iridium(III) emit bright blue to green light, was synthesized in five separate steps. Ir(F(2)MeOppy)(2)(acac), (acacH = 2,4-pentanedione), Ir(F(2)MeOppy)(2)(pic) (picH = 2-picolinic acid), fac-Ir(F(2)MeOppy)(3) and mer-lr(F(2)MeOppy)(3) complexes were synthesized from solution and fully characterized. The structures of Ir(F(2)MeOppy)(2)(acac) and fac-Ir(F(2)MeOppy)(3) were authenticated by X-ray single crystal structure analysis. fec-Ir(F(2)MeOppy)(3) showed a much higher solution photoluminescence (PL) quantum efficiency and blue-shifted emission compared to its counter mer-isomer. All of the complexes showed reversible oxidations between 0.3 and 0.7 V versus the ferrocene/ferrocenium ion. The relative thermodynamic stability of the mer versus fac isomer was investigated and correlated to their corresponding redox and PL properties. Two electroluminescent (EL) devices (D-1 and D-2) were fabricated using the same blue Ir(F(2)MeOppy)(2)(acac) complex as a a dopant but with two different hole blockers, BCP and BAlq, and consequently BCP proved itself a good hole blocker for this type of system. The fabrication of another EL device (D-3) was carried out by using the same dopant, only replacing the host CBP by a wider band gap host, mCP which showed improved luminance, luminance yield and power efficiency (D-2: 133 cd m(-2) 0.66 cd A(-1), 0.22 lm W-1; D-3: 326 cd m(-2); 1.63 cd A(-1); 0.26 lm W-1). (C) 2004 Elsevier Ltd. All rights reserved.
Tuning of wavelengths: Synthesis and photophysical studies of iridium complexes and their applications in organic light emitting devices
(2004-01-13)
Laskar, IR
;
Chen, TM
;
應用化學系
;
Department of Applied Chemistry
We have prepared and characterized a series of substituted 2-phenylbenzthiazole (4-CF3, 4-Me, 4-OMe, 4-F, 4-CN, and 3-F) ligands. The intermediate di-irrido and the six-coordinated mononuclear iridium(III) dopants of the above ligands have been synthesized and characterized. These complexes are thermally stable between 275 and 300 degreesC depending upon the types and volatility of substituents. They emit bright yellow to orange light. The peak emission wavelengths of the dopants can be finely tuned depending upon the electronic properties of the substituents as well as their positions in the ring. In the absorption spectra, the (MLCT)-M-1 and (MLCT)-M-3 transitions have been resolved in the range of 385-450 nm. The long tail toward lower energies are assigned to (MLCT)-M-3 and (3)pi-pi(*) transitions, which gains intensity by mixing with the higher lying (MLCT)-M-1 state through the spin-orbit coupling of iridium(III). All complexes exhibit one electron oxidation and the oxidation potential values can be correlated with the Hammett substituent constants. The electroluminescent characteristics for the substituted and the unsubstituted complexes have been compared and discussed.