Electronic structures of organic molecular materials for organic electroluminescent devices studied by ultraviolet photoemission spectroscopy

Abstract

Electronic structures of evaporated films of five organic light-emitting and carrier-injecting materials for organic electroluminescent devices were studied by ultraviolet photoemission spectroscopy. The compounds examined were (i) light-emitting materials tris(8-hydroxyquinolino) aluminum (Alq3) and 1,2,3,4,5-pentaphenylcyclopentadiene, (ii) a hole-injecting material N,N′-bis(3-methylphenyl)-N,N′-diphenyl-[1,1′-biphenyl]-4,4′-diamine, and (iii) electron-injecting materials N,N′-diphenyl-1,4,5,8-naphthyletracarboxyldiimide and 1,3,5-tris(5-phenyl-1,3,4-oxadiazol-2-yl)benzene. The spectral features corresponding to the top parts of the valence states, which dominate the electric properties of the materials, were assigned by the comparison with the simulated density of states obtained from PM3 molecular orbital calculations. Using these calculations, the evolution of the electronic structure of each molecule from those of constituent parts was discussed. The characters of the unoccupied states obtained by these calculations were also presented. Using these data, the correlation between the ionization threshold energies determined by ultraviolet photoemission spectroscopy and the carrier-injecting and light-emitting properties were discussed.

Porphyrin‐Based Molecular Rotors as Fluorescent Probes of Nanoscale Environments

“…This is in agreement with energyminimized structures of N,N′-diphenyl-NDI, [39] and of the related N-phenyl-1,8-naphthalimide, [33,34] that predict that the plane of the N-aryl substituent adopts a near orthogonal conformation relative to the plane of the (di)imide moiety. Calculations at the MP2/6-31G* level on N-phenyl-1,8-naphthalimide suggest that the conformation in which the naphthalimide and the N-phenyl substituent are coplanar is 60.1 kJ mol -1 higher in energy than the orthogonal conformation.…”

Organic/Organic′ Heterojunctions: Organic Light Emitting Diodes and Organic Photovoltaic Devices

“…Comparable studies have been previously conducted on OLED materials. [189,227,[230][231][232] Figure 4 shows representative UPS and OPV data for O/ O 0 heterojunctions based on the donors titanyl phthalocyanine (TiOPc, the ''phase I'' polymorph), [23] or copper phthalocyanine (CuPc) and the acceptor C 60 . [23,208] Starting with thin films of C 60 ( Figure 3B, F) the HOMO photoionization peaks from the fullerene are gradually replaced with those from the Pc with each successive deposition cycle.…”

Metal hybridization and electronic structure of Tris(8-hydroxyquinolato)aluminum (Alq3)

“…Hence the peak "A" is due to the true HOMO and not an interface state as suggested in other studies [6,15]. symbol: , ■-this work; □ [3]; × [4]; ▲ [5]; *,▼ [6]; , • [14];  [16]; | [17]; ○ [18]; +,  [19]; ♦ [20]. With the deposition of Alq 3 on gold, the thin adlayers of Alq 3 are periodic in the direction normal to the surface.…”