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.