Browsing by Author "Reddy, DS"

Now showing 1 - 5 of 5

Novel oxadiazole-containing polyfluorene with efficient blue electroluminescence
(2003-01-14)
Wu, FI
;
Reddy, DS
;
Shu, CF
;
Liu, MS
;
Jen, AKY
A novel oxdiazole-containing polyfluorene copolymer (PF-OXD) was synthesized by attaching two electron-deficient, 4-tent-butylphenyl-1,3,4-oxadiazole groups onto the C-9 position of the alternating fluorene unit to form a 3-D cardo-structure. This polymer possesses a very high glass transition temperature (T-g: 213 degreesC) and very good thermal stability due to its rigid cardo-linkage. The results from the photoluminescence measurements of the isothermally heated PF-OXD thin film (150 degreesC for 20 h) show that the commonly observed aggregate/excimer formation in polyfluorenes is very effectively suppressed in this polymer due to its 3-D structure and high T-g. A double-layer LED device using this polymer as the emitting layer shows a bright blue emission with a low turn-on voltage at 5.3 V and a high brightness of 2770 cd/m(2) at a drive voltage of 10.8 V. The maximum external quantum efficiency is 0.52% at 537 cd/m(2) with a bias of 7.4 V. The improved device performance over that of poly(9,9-dioctylfluorene) (POF) may be due to better electron injection and transport in PF-OXD and the efficient energy transfer from the OXD side chain to the polyfluorene main chains.
Synthesis and characterization of soluble poly(ether imide)s based on 2,2 '-bis(4-aminophenoxy)-9,9 '-spirobifluorene
(2003-02-01)
Reddy, DS
;
Chou, CH
;
Shu, CF
;
Lee, GH
;
應用化學系
A series of aromatic poly(ether imide)s containing 9,9'-spirobifluorene moieties in the main chain have been synthesized via the polycondensation of 2,2'-bis(4-aminophenoxy)-9,9'-spirobifluorene with a variety of aromatic dianhydrides. In the diamine monomer, the two aminophenoxyfluorene entities are orthogonally arranged and are connected through an sp(3) carbon atom (the spiro center). The resulting poly(ether imide)s have a polymer backbone which is periodically twisted with an angle of 90degrees at each spiro center. This structural feature, which restricts the close packing of the polymer chains and reduces inter-chain interactions, leads to amorphous poly(ether imide)s with good solubility in common organic solvents. In addition, the rigidity of the main chain of these polymers appears to be preserved due to the spiro-structure. As a result, these poly(ether imide)s exhibit a high T-g and excellent thermal stability. (C) 2002 Elsevier Science Ltd. All rights reserved.
Synthesis and characterization of soluble polyimides derived from 2,2 '-bis(3,4-dicarboxyphenoxy)-9,9 '-spirobifluorene dianhydride
(2002-01-15)
Reddy, DS
;
Shu, CF
;
Wu, FI
;
應用化學系
;
Department of Applied Chemistry
The synthesis of aromatic poly(ether imide)s containing spirobifluorene units in the polymer backbone is described. 2,2'-Bis(3,4-dicarboxyphenoxy)-9,9'-spirobifluorene dianhydride, which was used as a new monomer, was synthesized with 2,2'-dihydroxy-9,9'-spirobifluorene as the starting material. In the spiro-segment, the rings of the connected bifluorene were orthogonally arranged. This bis(ether anhydride) monomer was employed in reactions with a variety of aromatic diamines to furnish poly(ether imide)s, involving an initial ring-opening polycondensation and subsequent chemically induced cyclodehydration. Excellent solubility in common organic solvents at room temperature, good optical transparency, and high thermal stability are the prominent characteristic features of these new polymers, which can be attributed to the presence of spiro-fused orthogonal bifluorene segments along the polymer chain. The glass-transition temperatures of the polyimides were 240-293 degreesC, and the 5% weight-loss temperatures were greater than 500 degreesC. (C) 2001 John Wiley & Sons, Inc.
Synthesis and characterization of spiro-linked poly(terfluorene): a blue-emitting polymer with controlled conjugated length
(2002)
Wu, FI
;
Dodda, R
;
Reddy, DS
;
Shu, CF
;
應用化學系
The synthesis and characterization of a fluorene-spirobifluorene alternating copolymer, P(OF-SBF), are described. In the case of the spiro-segment, the two fluorene rings are orthogonally arranged and connected through a tetrahedral bonding carbon atom ( the spiro center). As a consequence, the polymer chain periodically zigzags, with an angle of 90degrees at each spiro center. This structural feature not only preserves the rigidity of the polymer chain but also prevents the pi-stacking of the polymer backbone, resulting in an improvement in both thermal and spectroscopic stabilities. Comparing the absorption and emission spectra of P(OF-SBF) and of a terfluorene model compound, it was revealed that P(OF-SBF) possesses a well-defined conjugation length. The polymer can serve as a host matrix to effectively transfer its excitation energy to a derivatized perylene dopant, yielding an efficient blue-light-emitting layer.
Synthesis and characterization of spirobifluorene-based polyimides
(2002-11-01)
Chou, CH
;
Reddy, DS
;
Shu, CF
;
應用化學系
;
Department of Applied Chemistry
The synthesis and properties of organosoluble aromatic polyimides, containing spiro-skeletal units in the polymer backbone on the basis of the spiro-diamine monomer, 2,2'-diamino-9,9'-spirobifluorene, are described. In the case of the Spiro segment, the two fluorene rings are orthogonally arranged and connected through a tetrahedral bonding carbon atom, the Spiro center. As a consequence, the polymer chain is periodically zigzagged with a 90degrees angle at each Spiro center. This structural feature minimizes interchain interactions and restricts the close packing of the polymer chains, resulting in amorphous polyimides that have good solubility in organic solvents. Compared with their fluorene-based cardo analogues, the spirobifluorene-based polyimides have an improved solubility. Furthermore, the main-chain rigidity of the polyimide appears to be preserved because of the presence of the spiro structure, which restricts the free segmental mobility. As a result, these polyimides exhibit a high glass-transition temperature (T-g's) and good thermal stability. The T-g's of these polyimides were in the range of 287-374 degreesC, and the decomposition temperatures in nitrogen for a 10% weight loss occurred at temperatures above 570 degreesC. (C) 2002 Wiley Periodicals, Inc. J Polym, Sci Part A: Polym Chem 40: 3615-3621, 2002.