Journal of Nonlinear Optical Physics & Materials

We synthesized and characterized novel highly phenyl-substituted spirobifluorene and carbazole derivatives such as 3,6-bis[(2,3,4,5-tetraphenyl)phenyl]-9-ethylcarbazole (BTPEC); 3,6-bis(7,10-diphenyl-fluoranthene)-9-ethylcarbazole (BDFEC); 2,7-Bis[(2,3,4,5-tetraphenyl)phenyl]-9,9′-spirobifluorene (BTPSF); and 3,6-bis(7,10-diphenyl-fluo-ran-thene)-9,9′-spirobifluorene (BDFSF), through Diels–Alder reaction. BDFEC showed sky blue PL spectrum at 481 nm and BTPSF showed ultra-violet PL spectrum at 374 nm in chloroform solution. Also BTPEC and BDFSF exhibited PL spectrum at around the UV region, 390 and 467 nm.

We have synthesized N-alkylated carbazole with a variation of alkyl size such as ethyl, hexyl, dodecyl and octadecyl group and have made thin film by using the spin-coating method. When N-octadecyl carbazole (NOC) film is made on ITO, the surface of the ITO/NOC layer becomes flatter compared to ITO and ITO/other N-alkylated carbazole layer. As the pendent alkyl chain length of carbazole becomes longer, the PL spectrum of the carbazole derivative becomes smooth and the PL maximum value is slightly shifted to long wavelength. ITO/NOC (100 nm)/LiF (1 nm)/Al (200 nm) device showed typical I-V characteristics and very weak blue EL light.

White light emission was obtained from a light-emitting diode prepared from polymer/quantum dot nanocomposites consisting of poly(9,9′-dihexylfluorene-2,7-divinylene-m-phenylenevinylene-stat-p-phenylenevinylene) (PDHFPPV) and CdSe nanoparticles. Blue emission from PDHFPPV and red emission from the nanoparticles, which is triggered by partial excitation energy transfer from PDHFPPV, jointly contribute to white emission of the organic/inorganic hybrid device. Also, the blue-emitting matrix polymer makes the device preparation process simpler due to its high processability. By controlling the blend ratio, we could obtain a pure white color from the hybrid device.

The potential blue-emitting as well as electron-transporting materials, 2,5-bis(3,5-trifluoromethylphenyl)-1,1-dimethyl-3,4-diphenylsilole (silole = silacyclopentadiene) (1) and 2,5-bis(3,5-trifluoromethylphenyl)-1,1-diphenyl-3,4-diphenylsilole (2), were synthesized by the Pd-mediated cross coupling reaction of corresponding bis(pheny-lethynyl)silanes with 1-bromo-3,5-trifluoromethylbenzene via intramolecular reductive cyclization. The structure of 2 was established by single-crystal X-ray diffraction analysis. In crystal structure, the dihedral angle between the functionalized phenyl groups containing CF₃ at 2,5-position and central silole ring is about 48.70(6)°, showing the diminution of effective conjugation. These compounds exhibited high thermal stability without degradation up to 200°C. The absorption and photoluminescent properties, and cyclic voltametry have been evaluated. Compounds 1 and 2 in thin films showed intense blue emissions at 464–473 nm, respectively, in photoluminescence (PL). In electrochemistry, the reduction potential of 1 and 2 were at -1.92 and -1.81 V, respectively. The presence of substituents at 2,5′ — and/or 1,1′ — positions of siloe ring affected the LUMO energy levels through σ*–π* conjugation.

We prepared the photorefractive composite based on organic–inorganic hybrid materials containing charge-transporting molecules, second-order nonlinear optical chromophore, photosensitizer, and plasticizer either as a side chain unit or a guest molecule. New chromophore was synthesized to contain nonlinear optical chromophore and carbazole in one molecule. The functional chromophores were reacted to isocyanatotriethoxysilane to provide the functional precursor molecules. 2,4,7-Trinitrofluorenone (TNF) was added into the sol-gel materials to induce a charge-transfer complex. We also compared the gain coefficient of the photorefractive samples with the change of the concentration of the plasticizer, determined by two-beam coupling technique.

A novel light-emitting aluminum complex (PAl) containing the dihydroxy derivative of trans-1,2-dipyridylethene, α-pyridoin, was synthesized and its electroluminescent (EL) properties characterized. The chemical structure of the complex was elucidated by FT-IR, UV-Vis and XPS. The complex showed thermal stability up to 350°C under nitrogen flow by TGA. The photoluminescence (PL) was measured from PAl cast film on quartz plate. Electroluminescent device having the structure of ITO/TPD/PAl/Al was fabricated by vacuum deposition, where N,N-bis(3-methylphenyl)-N,N′-diphenylbenzidine (TPD) was used as a hole transporting layer. The device emitted blue-green light of around 480 nm. The maximum luminance of 38 cd/m² and current density of 0.09 mA/cm² were observed at 34 V.

The cuplike structure of calix[4]arenes is one of the most attractive features, which has been observed both in the solid state and in solution. The newly synthesized 5,11,17,23-tetrakis(3-mercaptopropyl)calix[4]arene (1) and 25,26,27,28-tetrakis(5-mercaptopenthoxy)calix[4]arene containing aryl sulfide rings (2), have four alkyl thiol linkages, which allow the calixarenes to attach onto the gold surface. Surface plasmon resonance (SPR) spectroscopy allows us to monitor the binding of calixarene derivatives on the gold surface. The 1 and 2 bind very effectively on the gold surface and self-assembled layers of 1 and 2 produce significant change in SPR signals in 30 min. Calixarenes layers are used as platforms for molecular recognition, where complementary binding sites are easily and selectively introduced. The aromatic molecules used in this study are anthracene, pyrene, coronene and rubrene. The host-guest properties of these aromatic molecules and the calixarene cavity exhibit selectivity of these aromatic molecules. The anthracene, pyrene and coronene have moderate binding affinity to the cavity, and the rubrene does not bind at all.

Studies on the formulation of photosensitive paste for transparent soft mold press (TSMP) method have been performed. With the optimum formulation of the photosensitive paste the box-type barrier rib with good flexibility and high solvent resistance was fabricated, suitable for the panel material of the electrophoretic display. Cationically-charged white particles were prepared by using TiO₂ nanoparticles, silane coupling agent with amino groups, dispersant and acetic acid. The cationically charged TiO₂ particles exhibited 74.09 mV of zeta potential and 3.11 × 10^-5 cm²/Vs of mobility. Electrophoretic display fabricated with the charged TiO₂ particles exhibited 10 V of low driving voltage and maximum contrast ratio (5.3/1) at 30 V.

Phosphorescent materials, IR-FPPA1, IR-PPA1 and IR-TPA1 as emission dopants for electroluminescent (EL) devices were synthesized. Three types of devices such as ITO/ NPD/IR-FPPA1 (6%), IR-PPA1 (6%) and IR-TPA1 (6%) in CBP/BCP/Alq/LiF/Al were fabricated. IR-FPPA1, IR-PPA1 and IR-TPA1 exhibited 540 Cd/m², 6600 Cd/m² and 590 Cd/m² with their external quantum efficiency of 1.2%, 8.9% and 3.0% in current densities of 20 mA/cm², respectively. EL spectra of the IR-FPPA1, IR-PPA1, and IR-TPA1 devices had the band maxima at 490 nm, 535 nm and 615 nm, respectively.

A new blue electroluminescent conjugated polymer, poly(BP-alt-BCV), was prepared by Hornor–Emmons polycondensation of [5-carbazol-9-yl-3-(diethoxy-phosphorylmethyl)-2-(2-ethyl-hexyloxy)-benzyl]-phosphonic acid diethyl ester (PHBP) and 4,4′-biphenyldicarboxaldehyde (BPCA) in the presence of tert-BuOK in THF. UV-visible absorption maximum (λ_max,UV, π-π* transition) of poly(BP-alt-BCV) was measured at 340 nm. PL maximum (λ_max,PL) values of poly(BP-alt-BCV) were obtained at 406 and 430 nm, when excited at its own λ_max,UV. It was found that double layer [ITO/poly(BP-alt-BCV)/Alq₃ (50 Å)/Al] PLED exhibited maximum EL peak at 440 nm and blue emission (x = 0.1794, y = 0.1878), similar to the NTSC standard blue (x = 0.14, y = 0.08).

Polyazomethine-type conjugated polymers were synthesized by Schiff-base reaction. One was poly(PZ-PBI) with alternating phenothiazine (PZ) and azomethine units (-C = N-), and the other was poly(CZ-PBI) comprising alternating carbazole (CZ) and azomethine groups. Conjugated polymers exhibited improved solubility in common organic solvents due to alkyl side chains on phenothiazine and carbazole rings as well as polar azomethine groups in main chains. Single- and double-layer PLEDs were fabricated. Their electroluminescent properties were studied from the viewpoint of polymer structure vs. emission color and efficiency.

We have designed and developed novel lanthanide(III)-cored supramolecular systems with light-harvesting dendritic arrays for advanced photonics applications such as planar waveguide amplifiers, plastic lasers, and light-emitting diodes. The supramolecular ligands, such as naphthalenes and metalloporphyrins, were specially designed and synthesized in order to provide enough coordination sites to form stable lanthanide(III)-chelated complexes. The energy levels of the supramolecular ligands were tailored to maintain the effective energy transfer process from supramolecular ligands to lanthanide(III) ions for getting a higher optical amplification gain. Also, efficient energy transfer pathways for the sensitization of lanthanide ions by supramolecular ligands were investigated, for the first time to the best our knowledge. Furthermore, to enhance the optophysical properties of novel supramolecular systems, aryl ether-functionalized dendrons as photon antennas have been incorporated into lanthanide-cored supramolecular systems, yielding novel lanthanide-cored dendritic materials with efficient site-isolation effect.

We have designed and synthesized novel thermally stable perfluorinated polyimides with pendant perfluorinated aromatic unit for photonic applications. At first, we developed a new synthetic route to a perfluorinated aromatic diamine by protecting-deprotecting as well as by nucleophilic bromine displacement reactions, affording a new diamine with a pendant perfluorinated aromatic unit. Its chemical structure was identified by ¹H-, ¹⁹F- and ¹³C-NMR spectroscopies as well as mass spectrometry. Novel fluorinated polyimides were prepared by condensation polymerization of the present fluorinated diamine with various dianhydrides. The resultant polyimides are thermally stable over 400°C. The refractive index and birefringence of the resultant polyimides are 1.5844 ~ 1.5040 and 0.01 ~ 0.03 at 633 nm, respectively.

Poly(9,9-dipropargylfluorene) [PDPF] was prepared via oxidative coupling reaction of dipropargylfluorene in the presence of (PPh₃)₂PdCl₂/CuI without oxygen in high yield. The polymer structure was characterized by the instrumental methods such as NMR, IR, and UV-visible spectroscopies to have the designed chemical structure. PDPF showed characteristic UV-visible absorption band at 338 nm and blue PL spectrum at 417 nm corresponding to the photon energy of 2.98 eV under the excitation wavelength of 350 nm. The bandgap energy of this material was estimated to be 3.67 eV from the analysis of the absorption edge.