ABSTRACT:The relationships between the color intensities of polyimide films and the electronic properties of their source materials-aromatic diamines and aromatic tetracarboxylic dianhydrides-are discussed. The arrangement of the diamine moieties in order of color intensity of polyimides shows fairly good agreement with the order of the electron-donating properties of the diamines estimated from 15 N NMR chemical shifts (bN). On the other hand, the arrangement of the dianhydrides moieties in order of color intensity of polyimides agrees with the order of the electron-accepting properties of the dianhydrides estimated from experimental and calculated electron affinity (EA) although systematic inconsistencies are observed for the dianhydrides having-CF 3 groups and a benzophenone carbonyl group. These results are consistent with the formation of charge transfer complex (CTC) and indicate that the electron-donating properties of diamines and electron-accepting properties of dianhydrides are retained to a significant extent even in polyimide molecular chains. KEY WORDSPolyimide / Coloration / Charge Transfer Complex / Dianhydride / Diamine / Nuclear Megnetic Resonance Chemical Shift / MNDO-PM3 / Optical transparency of polyimide films is of special importance in some applications such as flexible solar radiation protectors, 1 orientation films in liquid crystal display devices, 2 optical waveguides for communication interconnects, 3 and optical half-waveplates for planar lightwave circuits. 4 However, most of the conventional polyimide films always show considerable coloration ranging from pale yellow to deep brown. Rogers 5 first reported that optically transparent and colorless polyimides can be synthesized from a dianhydride and a diamine that have hexafluoroisopropyridene (-C(CF 3 ) 2-) groups. We have reported that the fluorinated polyimides derived from 2,2' -bis(trifluoromethyl)-4,4'-diaminobiphenyl (TFDB) exhibit excellent properties needed for optical applications. 6 In particular, the polyimide derived from 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) and TFDB show no color, high transparency in the visible region, and low optical transmission losses in the near-infrared region as well as low dielectric constants, low refractive indices, and low water absorption. The idea that fluorination of dianhydride and diamine moieties give colorless polyimides are widely accepted. On the other hand, we have recently reported the first synthesis of perfluorinated polyimides that have very high optical transparency over the entire range of optical communication wavelengths (1.0--1.7 µm) and high glass transition temperatures over 300°C. 7 • 8 Despite the high fluorination of the diamine and dianhydride, the perfluorinated polyimides show considerable coloration ranging from orange to brown. This fact indicates that the fluorination of source materials does not necessarily lead to colorless polyimides. If the coloration of polyimide films can be predicted from the properties of their source materia...

Novel pi-electron systems with trifluoromethylphenyl groups and/or a thiazolothiazole unit were developed as n-type semiconductors for OFETs. They showed excellent n-type performances with high electron mobilities. The trifluoromethylphenyl group was found to be very effective in inducing n-type behavior. The thiazolothiazole unit was favorable for forming stacking structures leading to efficient intermolecular pi-pi interactions.

Novel thiazole oligomers and thiazole/thiophene co-oligomers with trifluoromethylphenyl groups were developed as n-type semiconductors for OFETs. They showed excellent n-type performances with high electron mobilities. A 5,5'-bithiazole with trifluoromethylphenyl groups forms a closely packed two-dimensional columnar structure leading to a high performance n-type FET. The electron mobility was enhanced to 1.83 cm2/Vs on the OTS-treated substrate.

Helices have long attracted the attention of chemists, both for their inherent chiral structure and their potential for applications such as the separation of chiral compounds or the construction of molecular machines. As a result of steric forces, polymeric o-phenylenes adopt a tight helical conformation in which the densely packed phenylene units create a highly condensed π-cloud. Here, we show an oligomeric o-phenylene that undergoes a redox-responsive dynamic motion. In solution, the helices undergo a rapid inversion. During crystallization, however, a chiral symmetry-breaking phenomenon is observed in which each crystal contains only one enantiomeric form. Crystals of both handedness are obtained, but in a non-racemic mixture. Furthermore, in solution, the dynamic motion of the helical oligomer is dramatically suppressed by one-electron oxidation. X-ray crystallography of both the neutral and oxidized forms indicated that a hole, generated upon oxidation, is shared by the repeating o-phenylene units. This enables conformational locking of the helix, and represents a long-lasting chiroptical memory.

A series of inorganic/organic composite films exhibiting high thermal stability and high thermal diffusivity was prepared from five different grades of flake-shaped hexagonal boron nitride (hBN) and aromatic polyimides (PIs). Thermal diffusivities along the out-of-plane (D(perpendicular)) and in-plane (D//) directions of hBN/PI films were separately measured and analyzed in terms of particle size, shape, concentration, and orientation, as well as molecular structures of rigid and flexible PI matrices. hBN/PI films filled with large flake-shaped particles exhibited a large anisotropy in D(perpendicular) and D// due to the strong in-plane orientation of heat-conducting basal plane of hBN, while smaller anisotropy was observed in composites with small flakes and aggregates which tend to orient less in the in-plane direction during film processing. The anisotropic thermal diffusion property observed in hBN/PI films exhibited strong correlation with the orientation of hBN particles estimated using scanning electron micrographs (SEM) and wide-angle X-ray diffraction. Moreover, composites of hBN with a rigid-rod PI matrix exhibited much larger anisotropy in D(perpendicular) and D// than flexible PI-composites, reflecting the effect of the rigid and densely packed PI chains preferentially orienting parallel to the film plane. The thermal conductivities of the hBN/rigid-rod PI films were estimated as 5.4 and 17.5 W/m·K along the out-of-plane and in-plane directions, respectively, which is one of the largest values ever reported.

A new series of star‐shaped bipolar host molecules, tris(4′‐(1‐phenyl‐1H‐benzimidazol‐2‐yl)biphen‐yl‐4‐yl) amine (TIBN), tris(2′‐methyl‐4′‐(1‐phenyl‐1H‐benzimida zol‐2‐yl)biphenyl‐4‐yl)amine (Me‐TIBN), and tris(2,2′‐dimethyl‐4′‐(1‐phenyl‐1H‐benzimidazol‐2‐yl)biphenyl‐4‐yl)amine (DM‐TIBN), that contain hole‐transporting triphenylamine and electron‐transporting benzimidazole moieties are designed based on calculations using density functional theory and successfully prepared. The theoretical calculation of energy levels of TIBN derivatives affords helpful ideas to design molecules with a favorable localization of highest occupied/lowest unoccupied molecular orbital (HOMO/LUMO) levels and a predefined enhancement of the triplet energy gap. The TIBN derivatives are employed as hosts to fabricate phosphorescent organic light‐emitting diodes (OLEDs) by the two methods of spin‐coating and vacuum deposition. Notably, the spin‐coated Me‐TIBN and DM‐TIBN devices exhibit a much better performance than the vacuum‐deposited ones, in which the spin‐coated DM‐TIBN device (47 500 cd m−2, 27.3 cd A−1, 7.3 lm W−1) is outstanding with respect to other seminal work for solution‐processed OLEDs. More importantly, the new concept of localizing HOMO and LUMO levels for bipolar molecules is illustrated, and a facile strategy to tailor the energy levels by breaking the conjugation of hole‐ and electron‐transporting moieties is demonstrated.

High refractive aromatic polyimides (PIs) containing a thianthrene-2,7-disulfanyl moiety in their main chain have been developed. The PIs were prepared from a newly developed aromatic diamine 2,7-bis(4-aminophenylenesulfanyl)thianthrene (APTT) and several aromatic dianhydrides by a two-step polycondensation procedure. The relationships between the structures and the thermal, mechanical, and optical properties of the flexible, tough, transparent, and amorphous PI films were established. Introduction of the thianthrene-2,7-disulfanyl group endowed the PIs with good combined properties, including high thermal stability with 10% weight loss temperatures (T 10%) higher than 500 °C in nitrogen and the glass transition temperatures (T gs) higher than 200 °C, good transparency with transmittances higher than 80% at 500 nm, and refractive indices higher than 1.73 at 632.8 nm. Because of higher sulfur content, the refractive indices of the PIs we synthesized are higher than those of PIs derived from the other sulfur-containing diamines such as 4,4‘-(p-phenylenedisulfanyl)dianiline (2SPDA) and 4,4‘-thiobis[(p-phenylenesulfanyl)aniline] (3SDA). The PI derived from APTT and 4,4‘-[p-thiobis(phenylenesulfanyl)]diphthalic anhydride (3SDEA) has the highest sulfur content (23.2%) in its repeating units, and hence, it exhibits the highest refractive index, i.e., 1.7600.

A series of semialicyclic polyimides (PIs) have been successfully prepared by the polycondensation of two alicyclic dianhydrides, 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA) and 1,2,4,5-cyclohexanetetracarboxylic dianhydride (CHDA) with two sulfur-containing aromatic diamines, 4,4′-thiobis [(pphenylenesulfanyl)aniline] (3SDA) and 2,7-bis(4-aminophenylenesulfanyl)thianthrene (APTT), respectively, by a two-step polymerization procedure via the soluble poly(amic acid) (PAA) precursors. Flexible and tough PI films were obtained with a tensile strength greater than 82 MPa and elongation at breaks higher than 12%. The films showed good thermal and thermal-oxidative stability without significant weight loss up to 400 °C, both in air and nitrogen. The glass-transition temperatures of the PIs ranged from 236.5 to 274.1 °C. Good optical transparency, including the cutoff wavelengths lower than 350 nm and transmittances higher than 80% at 400 nm, was achieved for all the PI films. The refractive indices of the PI films were in the range of 1.6799-1.7130 measured at 632.8 nm, which agreed well with the values calculated by the time-dependent density functional theory (TD-DFT). In addition, PAA-II a (CHDA-3SDA) showed a good affinity with silica-modified TiO 2 nanoparticles. The hybrid system with 45 wt % load of TiO 2 nanoparticles, combined with the photobase generator N-{ [(4,5-dimethoxy-2-nitrobenzyl)oxy]carbonyl}2,6-dimethylpiperidine (DNCDP) exhibited good photolithographic characteristics. A fine negative pattern with a resolution of approximately 4 µm was successfully printed on the hybrid film. The cured PI-II a -TiO 2 hybrid film exhibited a refractive index of 1.8100 at 632.8 nm.