Chiitang Tsai

High Tg blue emitting materials for electroluminescent devices

A series of 2′,7′-di-tert-butyl-9,9′-spirobifluorene derivatives (flu) incorporating arylamines at the 2- and/or 7-positions were synthesized. These compounds possess a high glass transition temperature ranging from 135 to 215 °C. Incorporation of spirobifluorene was found to be beneficial for raising the glass transition temperature (Tg) of the molecules. Most of the compounds are blue emitting with good solution quantum yields. Blue-emitting double-layer devices with narrow full width at half-maximum (fwhm < 68 nm) were constructed using these materials as the hole-transporting and emitting layer, and TPBI (1,3,5-tris(N-phenylbenzimidazol-2-yl)benzene) as the electron-transporting layer (device I). In double-layer devices of the configuration ITO/flu (40 nm)/Alq3 (40 nm)/Mg : Ag (Alq3 = tris(8-hydroxyquinoline)aluminium) (device II), flu functioned mainly as a hole-transporting layer, and the green light characteristic of Alq3 was detected. Two of the devices of type I have very promising performance, and one of them emits pure blue light (CIE (x,y) = (0.15, 0.09)). One of the compounds was found to be an efficient hole-injection material.

High-performance dye-sensitized solar cells based on 5,6-bis-hexyloxy-benzo[2,1,3]thiadiazole

New dipolar compounds containing a 5,6-bis-hexyloxy-benzo[2,1,3]thiadiazole entity in the conjugated spacer between the electron donating arylamine and the electron accepting 2-cyanoacrylic acid have been synthesized. These compounds were used as the sensitizers for efficient dye-sensitized solar cells. Compared to the congeners without the hexyloxy chains, the new dyes effectively suppress the dark currents and significantly improve the cell performance. The best conversion efficiency reached ∼92% of the N719-based standard DSSC fabricated and measured under similar conditions (AM 1.5 irradiation).

Dihydrophenanthrene-based metal-free dyes for highly efficient cosensitized solar cells.

Metal-free dyes (BP-1 to BP-3) containing a 9,10-dihydrophenanthrene unit in the spacer have been synthesized. The dye with the highest cell efficiency, BP-2, was used in combination with SQ2 for cosensitized DSSCs. The cosensitized DSSC in which the ratio of BP-2 and SQ2 is 8:2 (v/v) has a record high efficiency of 8.14% among cosensitized systems using all metal-free sensitizers. Dye distribution along the TiO2 film depth was analyzed by an Auger electron spectroscopy technique.

H-Bonded effects on supramolecular liquid crystalline trimers containing photoluminescent cores

Several series of hydrogen-bonded (H-bonded) liquid crystalline trimers are constructed by complexation of two complementary components containing various bifunctional photoluminescent (PL) acceptor cores and monofunctional proton donors (in a 1∶2 molar ratio). These supramolecular liquid crystalline trimers (i.e. H-bonded trimers 1/3, 1/4, 1/5, 1/6, 2/3, 2/4, 2/5 and 2/6) are, respectively, obtained from bifunctional bis-pyridyl acceptors (containing conjugated benzene and thiophene centers) (1 and 2) complexed with monofunctional carboxylic acids (containing benzene, thiophene or naphthalene) (3–6) in a 1∶2 acceptor–donor group stoichiometry. Though the PL bis-pyridyl acceptors (1 and 2) do not possess any mesophases, the distinct mesomorphism and supramolecular architecture of these H-bonded trimers are confirmed by polarizing optical microscopy (POM), DSC, and powder X-ray diffraction (XRD) experiments. Moreover, the PL properties of the photoluminescent bis-pyridyl cores can be adjusted not only by the central structures of the cores but also by their surrounding non-photoluminescent proton donors. In general, redder shifts occur in PL spectra of H-bonded trimers when proton donors of smaller pKa values are H-bonded to the photoluminescent cores. Significantly, different wavelengths and polarized light of PL emission can be obtained in these supramolecular structures possessing both liquid crstalline and photoluminescent properties.

Preparation of push-pull type chromophores via nitrothiophene induced Michael type reaction of alkynes

Abstract Nitrothiophene activates a neighboring alkyne to undergo Michael addition with dialkylamines and methanol to afford push-pull type chromophores. These compounds exhibit a large positive solvatochromism. The olefinic moiety in (Z)-(((5-nitrothien-2-yl)methylene)-(ferrocenyl)methyl)diethylamine (14) can be converted to an α-diketone.