Multilayer organic electroluminescent devices (OELDs) were fabricated with highly pure 2-(2-hydroxyphenyl)benzoxazolato lithium (LiPBO), which was obtained through stepwise purification process, as a blue emission layer. The ionization potential of the carefully purified LiPBO was ∼5.82 eV. The multilayer OELD with a hole-blocking layer (HBL) emitted almost pure blue light with the CIE color coordinate of x=0.15 and y=0.08. However, the emission color was redshifted when an electron-transporting layer (ETL) was introduced instead of the HBL. The device with both the HBL and the ETL showed stable and bright blue emission above 14 000 cd/m2 with the color coordinate of x=0.15 and y=0.11, even though the color purity was slightly poorer than that with only the HBL.

A novel hole injecting and transporting polymer, poly[N,N ‘-diphenyl-N,N ‘-bis(4-aminobiphenyl)-(1,1‘-biphenyl)-4,4‘-diamine pyromellitimide] (PMDA-DBABBD PI), was obtained by thermal imidization from its poly(amic acid) (PAA) made by the reaction of pyromellitic dianhydride with the DBABBD that was chemically reduced from N,N ‘-diphenyl-N,N ‘-bis(4-nitrobiphenyl)-(1,1‘-biphenyl)-4,4‘-diamine synthesized through the palladium-catalyzed amination. The materials were characterized by using 1H NMR, 13C NMR, FT-IR, HR GC-MS, EA, and DSC. The characteristics of the PAA or PI thin films were investigated with XPS and an impedance spectroscopy. The hybrid light-emitting devices (HOLEDs) with the PAA and PI thin films were fabricated to examine the performance of the polymeric thin films as a hole injecting and transporting layer. The PI thin film having the glass transition temperature of 200 °C showed stable characteristics in the application for the HOLED whereas the PAA thin film seemed to be unstable. The power efficiency of the HOLED with the PI thin film was 0.23 cd/A at 4000 cd/m2.

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Spectroscopic, redox, computational, and electron transfer reactions of the covalently linked zinc porphyrin-triphenylamine-fulleropyrrolidine system are investigated in solvents of varying polarity. An appreciable interaction between triphenylamine and the porphyrin pi system is revealed by steady-state absorption and emission, redox, and computational studies. Free-energy calculations suggest that the light-induced processes via the singlet-excited porphyrin are exothermic in benzonitrile, dichlorobenzene, toluene, and benzene. The occurrence of fast and efficient charge-separation processes ( approximately 10(12) s(-1)) via the singlet-excited porphyrin is confirmed by femtosecond transient absorption measurements in solvents with dielectric constants ranging from 25.2 (benzonitrile) to 2.2 (benzene). The rates of the charge separation processes are much less solvent-dependent, which suggests that the charge-separation processes occur at the top region of the Marcus parabola. The lifetimes of the singlet radical-ion pair (70-3000 ps at room temperature) decrease substantially in more polar solvents, which suggests that the charge-recombination process is occurring in the Marcus inverted region. Interestingly, by utilizing the nanosecond transient absorption spectral technique we can obtain clear evidence about the existence of triplet radical-ion pairs with relatively long lifetimes of 0.71 mus (in benzonitrile) and 2.2 mus (in o-dichlorobenzene), but not in toluene and benzene due to energetic considerations. From the point of view of mechanistic information, the synthesized zinc porphyrin-triphenylamine-fulleropyrrolidine system has the advantage that both the lifetimes of the singlet and triplet radical-ion pair can be determined.

A novel method for understanding the alignment mechanism was motivated by the texture observation of a nematic liquid crystal (LC) contacted with a photoaligned layer after rubbing. Reorientation of director occurs by subsequent photoalignment to different direction from that forced by rubbing. Moreover, it was found by polarized absorption spectra that the preferential average main chain axis over whole the alignment layer does not change, indicating that the orientation change by photoalignment occurs only at very top surfaces. This experiment without changing surface morphology indicates that the alignment priority for the nematic LC is mainly governed by the anisotropic short-range intermolecular interaction between alignment films and LC molecules and the effect of microgrooves plays a minor role.

Director tilting of liquid crystal (LC) molecules on photosensitive alignment layers has been investigated. The layers, polyimides with photoisomerizable groups in their main chains, were irradiated with unpolarized near-UV (UPUV) light at oblique incidence. The irradiated film was found to align LC molecules homogeneously with a negligible pretilt angle. It was found that the pretilt angle can be generated successfully by introducing surfactant lecithin and decreasing the incidence angle of the UPUV light. The LC alignment and electro-optical properties of the LC cells with the photoalignment layers were demonstrated to be suitable for twisted nematic LC, vertical alignment LC, and surface-stabilized ferroelectric LC devices.

The high-electric-field technique was used to measure the out-of-plane (polar) anchoring strength at the interface between a nematic liquid crystal, pentylcyanobiphenyl (5CB), and a photosensitive polyimide (PI) alignment layer possessing an azo group in the main chain. The anchoring energy of the photoaligned state was found to be rather strong, on the order of 0.1 mJ/m2, being at least half of the anchoring energy on the rubbed surface of the same azo PI. The anchoring energy exhibited a conspicuous peak near the clearing temperature of 5CB, particularly in the photoaligned system, indicating a significant role of molecular motion in anchoring behavior.