Siriporn Jungsuttiwong

Bifunctional anthracene derivatives as non-doped blue emitters and hole-transporters for electroluminescent devices

New highly fluorescent bifunctional anthracenes showed high thermal and electrochemical stability, and great potential as both blue emitters and hole-transporters for OLEDs. Deep-blue and Alq3-based green devices with maximum efficiencies and CIE coordinates of 1.65 and 6.25 cd A(-1), and (0.15, 0.16) and (0.26, 0.49) were achieved, respectively.

Blue light-emitting and hole-transporting materials based on 9,9-bis(4-diphenylaminophenyl)fluorenes for efficient electroluminescent devices

New bifunctional materials namely BTTF, TPTF and BPTF having 9,9-bis(4-diphenylaminophenyl)fluorene as a molecular platform were synthesized and characterized. These molecules showed strong blue emission in both solution and solid state with a solution fluorescence quantum efficiency of up to 74% and were thermally stable amorphous materials with glass transition temperature well above 170 °C. The abilities of these materials as blue light-emitting materials for blue OLEDs and hole-transporting materials for green OLEDs in terms of device performance and thermal property were superior to a commonly used N,N′-diphenyl-N,N′-bis(1-naphthyl)-(1,1′-biphenyl)-4,4′-diamine (NPB). Efficient non-doped blue and Alq3-based green OLEDs with maximum luminance efficiencies and CIE coordinates of 2.06 cd A−1 and (0.15, 0.13), and 4.94 cd A−1 and (0.29, 0.52) were achieved, respectively, with BPTF having two pyrene substituents as the emitting layer and the hole-transporting layer, respectively.

Pyrene-functionalized carbazole derivatives as non-doped blue emitters for highly efficient blue organic light-emitting diodes

A series of pyrene-functionalized carbazole derivatives, namely N-dodecyl-3,6-di(pyren-1-yl)carbazole (CP2), N-dodecyl-1,3,6-tri(pyren-1-yl)carbazole (CP3) and N-dodecyl-1,3,6,8-tetra(pyren-1-yl)carbazole (CP4), are synthesized and characterized as simple non-doped solution processed blue emitters for OLEDs. By multiple substitution of pyrene on the carbazole ring, we are able to retain the high blue emissive ability of pyrene in the solid as well as improve the amorphous stability and solubility of the material. These materials show high solution fluorescence quantum efficiencies (up to 94%) and can form morphologically stable amorphous thin films with Tg as high as 170 °C. Solution processed double-layer OLEDs using these materials as non-doped blue emitters exhibit good device performance with luminance efficiencies up to 2.53 cd A−1. Their multi-layer devices exhibit outstanding performances. The CP2-based device shows a low turn-on voltage (down to 2.6 V) with an excellent blue emission color (λem = 436 nm) and CIE coordinates of (0.16, 0.14), while the CP3 and CP4-based blue devices also display low turn-on voltages (down to 2.7 V) with high luminance (up to 24479 cd m−2) and luminance efficiencies (up to 6.92 cd A−1).

Carbazole-dendrimer-based donor-π-acceptor type organic dyes for dye-sensitized solar cells: effect of the size of the carbazole dendritic donor.

A series of novel D-π-A type organic dyes, namely, GnTA (n = 1-4), containing carbazole dendrons up to fourth generation as a donor, bithiophene as π-linkage, and cyanoacrylic acid as acceptor were synthesized and characterized for applications in dye-sensitized solar cells (DSSCs). The photophysical, thermal, electrochemical, and photovoltaic properties of the new dyes as dye sensitizers were investigated, and the effects of the carbazole dendritic donors on these properties were evaluated. Results demonstrated that increasing the size or generation of the carbazole dendritic donor of the dye molecules enhances their total light absorption abilities and unluckily reduces the amount of dye uptake per unit TiO2 area because of their high molecular volumes. The latter was found to have a strong effect on the power conversion efficiency of DSSCs. Importantly, electrochemical impedance spectroscopy (EIS) revealed that the size or generation of the donor had a significant influence on a charge-transfer resistance for electron recombination at the TiO2/electrolyte interface, causing a difference in open circuit voltage (Voc) of the solar cells. Among them, dye G1TA containing first generation dendron as a donor (having lowest molecular volume) exhibited the highest power conversion efficiency of 5.16% (Jsc = 9.89 mA cm(-2), Voc = 0.72 V, ff = 0.73) under simulated AM 1.5 irradiation (100 mW cm(-2)).

Novel Bis[5-(fluoren-2-yl)thiophen-2-yl]benzothiadiazole End-Capped with Carbazole Dendrons as Highly Efficient Solution-Processed Nondoped Red Emitters for Organic Light-Emitting Diodes

A series of novel red-emitting bis[5-(fluoren-2-yl)thiophen-2-yl]benzothiadiazole-cored dendrimers containing carbazole dendrons up to the third generation are synthesized. Their photophysical, thermal, electrochemical, and electroluminescent properties as nondoped solution-processed red light-emitters for OLEDs are investigated. By using carbazole dendrons as the end caps, we are able to reduce the crystallization and retain the high emissive ability of a planar fluorescent core in the solid state as well as improve the thermal stability of the material. These dendrimers show a bright-red fluorescence and can form morphologically stable amorphous thin films with glass-transition temperatures as high as 283 °C. Simple structured solution-processed OLEDs using these materials as hole-transporting nondoped emitters and BCP as the hole-blocking layer emit a stable red color around 622-645 nm, with high luminance efficiencies (up to 4.80 cd A(-1) at 1.2 mA cm(-2)) and CIE coordinates of (0.65, 0.33), which are close to the pure red color.

Theoretical investigation of novel carbazole-fluorene based D-π-A conjugated organic dyes as dye-sensitizer in dye-sensitized solar cells (DSCs).

The ground state structure and frontier molecular orbital of newly synthesized carbazole‐fluorene based D‐π‐A organic dyes, CFP1A, CFP2A, CFP1CA, and CFP2CA, were theoretically investigated using density functional theory (DFT) at B3LYP/6‐31G(d,p) level. These dye molecules have been constructed based on carbazole‐fluorene as the electron‐donating moiety while introducing benzene units as π‐spacer connected to different anchor groups, such as acrylic acid and cyanoacrylic acid, as acceptors. The electronic vertical excitation energies and absorption wavelength were carried out using time‐dependent DFT (TD‐DFT). Furthermore, the adsorptions of phenylacrylic acid and phenylcyanoacrylic acid on the TiO2 anatase (101) surface were carried out by means of quantum‐chemical periodic calculations employing periodic PBE functional with DNP basis set. The results promise that anchor dyes with strong withdrawing CN group have easier injected electron to the conduction band of semiconductor implying that CFP1CA and CFP2CA show better performance among four dyes. Additionally, the intramolecular charge transfers (ICT) from electron donor group to anchoring group of CFP1CA and CFP2CA have shown better performance. The calculated results provide the efficiency trend of our new dyes as CFP1CA ≈ CFP2CA > CFP1A ≈ CFP2A which are excellently agree with experimental observation.

Adsorption of carbon monoxide in H-ZSM-5 and Li-ZSM-5 zeolites: an embedded ab initio cluster study

The absorption of carbon monoxide with H-ZSM-5 and metal-substituted Li-ZSM-5 zeolites has been investigated by . using both cluster and embedded cluster approaches at the HFr6-31G d,p level of theory. For the H-ZSM-5 zeolite, the binding energy of CO on a 3T quantum cluster is predicted to be 2.25 kcalrmol for the C-bound complex. The O-bound complex was found to be less stable by about 0.84 kcalrmol. Inclusion of the Madelung potential was found to increase the acidity of the Bronsted acidic site and the CO-binding energy to 4.95 kcalrmol, consequently, it leads better agreement with experimental observation. Similar results were also obtained for the Li-ZSM-5rCO complex. The Madelung potential field from the zeolite framework was found to reverse the order of relative stability of C-bound and O-bound adducts in comparison to the Li q -CO system. q 2000 Elsevier Science B.V. All rights reserved.

Bis(carbazol-9-ylphenyl)aniline end-capped oligoarylenes as solution-processed nondoped emitters for full-emission color tuning organic light-emitting diodes.

A series of bis(3,6-di-tert-butylcarbazol-9-ylphenyl)aniline end-capped oligoarylenes, BCPA-Ars, are synthesized by double palladium-catalyzed cross-coupling reactions. By using this bis(carbazol-9-yl)triphenylamine moiety as an end-cap, we are able to reduce the crystallization and retain the high-emission ability of these planar fluorescent oligoarylene cores in the solid state, as well as improve the amorphous stability and solubility of the materials. The results of optical and electrochemical studies show that their HOMOs, LUMOs, and energy gaps can be easily modified or fine-tuned by either varying the degree of π-conjugation or using electron affinities of the aryl cores which include fluorene, oligothiophenes, 2,1,3-benzothiadiazole, 4,7-diphenyl-4-yl-2,1,3-benzothiadiazole, and 4,7-dithien-2-yl-2,1,3-benzothiadiazole. As a result, their emission spectra measured in solution and thin films can cover the full UV-vis spectrum (426-644 nm). Remarkably, solution-processed nondoped BCPA-Ars-based OLEDs could show moderate to excellent device performance with emission colors spanning the whole visible spectrum (deep blue to red). Particularly, the RGB (red, green, blue) OLEDs exhibit good color purity close to the pure RGB colors. This report offers a practical approach for both decorating the highly efficient but planar fluorophores and tuning their emission colors to be suitable for applications in nondoped and solution-processable full-color emission OLEDs.

An efficient solution processed non-doped red emitter based on carbazole–triphenylamine end-capped di(thiophen-2-yl)benzothiadiazole for pure red organic light-emitting diodes

New carbazole-triphenylamine end-capped di(thiophen-2-yl)benzothiadiazole showed high thermal and electrochemical stability, and great potential as a solution processed hole-transporting non-doped red emitter for OLEDs. A pure red device with CIE coordinates and a high luminance efficiency of (0.66, 0.33) and 3.97 cd A(-1), respectively, was achieved.

Linearly π-conjugated oligothiophenes as simple metal-free sensitizers for dye-sensitized solar cells

Four linear oligothiophenes containing 4, 5 and 7 thiophene rings substituted by a variable number of octyl chains attached at the beta-position of some of the thiophene rings and possessing a terminal cyanoacrylic acid anchoring group have been synthesized. Results of UV-Vis absorption spectroscopy and cyclic voltammetry show that as expected the extension of the π-conjugated system leads to a decrease of the optical gap with an increase of the HOMO level. The four compounds have been evaluated as sensitizers in dye-sensitized solar cells (DSSCs) using a iodide/triiodide liquid electrolyte and the results are discussed in terms of the structure–property relationship with regard to the extension of the conjugated system and the number and position of the octyl side chains using N719 as the reference system. A power conversion efficiency of ∼7.30% corresponding to 90% of the value given by N719 under identical conditions has been obtained with one of the heptamers.