Yusuke Kamura

Effect of Pressure on the Absorption Spectra of Oriented and Amorphous Organic Films

Abstract The absorption spectra of oriented and amorphous naphthacene and pentacene film have been measured at high pressure. The Davydov splitting of 0–0 band in oriented films increase with increasing pressure at the rate of 37 cm−1/kbar for naphthacene and 70 cm−1/kbar for pentacene. The 0–2 vibronic bands of both oriented films show the large red shifts compared with the 0–1 vibronic band. For amorphous films the Davydov splitting is not observed at atmospheric pressure. The pressure induced spectral red shifts in the amorphous state are slightly larger than those in the crystalline-state.

Near and vacuum ultraviolet absorption spectra of polycrystalline and amorphous evaporated films of naphthacene, pentacene, perylene and coronene

Abstract The near- and vacuum-ultraviolet absorption spectra of polycrystalline and amorphous films of naphthacene, pentacene, perylene evaporated on substrate at room and low temperatures have been measured at room temperature. The changes in the spectra are explained in terms of the loss of molecular orientation and the change in Davydov splitting. The spectra for coronene evaporated at room temperature are also reported.

High photo-response organic materials: tetrabenzo-[a,cd,j,lm]perylene and diphenanthra[4,5,6-abcd, 4,5,6-jklm]perylene

Abstract The photoconductivity of evaporated thin films of tetrabenzo[ a,cd,j,lm ] perylene and diphenanthra[4,5,6- abcd , 4,5,6- jklm ]perylene were observed. These compounds, particularly the latter, were found to show a very high photo-response even under a high vacuum. The time response of the photocurrent is very sharp under a high vacuum, so that the reliable spectral response of the photocurrent could be observed. The photocurrents increase successively by exposing the films to oxygen, but no effect is observed by exposing them to nitrogen and sulphur hexafluoride (SF 6 ).

Electrical conductivity, photoemission and absorption spectrum of tetraselenonaphthacene, C18H8Se4

Abstract The electrical conductivity, the photoemission and the absorption spectrum of tetraselenonaphthacene (TSN) evaporated film were studied. The conductivity of TSN film in a vacuum of 1.6 × 10−8 torr was 7.7 × 10−7 Ω−1 cm−1. When the film was exposed to air at atmospheric pressure, the value of the conductivity was found to be 1.1 × 10−4 Ω−1 cm−1. The ionization potential of the film estimated from its electron spectroscopy energy distribution curve was 4.45 eV. The absorption band at 15 400 cm−1 was insensitive to the pressure; on the contrary the band at 11 900 cm−1 showed a large red-shift at the rate of 120 cm−1/kbar. The remarkable difference in the pressure shift of the absorption bands in TSN film may arise from the Davydov splitting.

Electrical conductivity of hexaiodobenzene and tetrahalo-p-benzoquinone under very high pressures

Abstract The electrical resistances of hexaiodobenzene, iodanil, bromanil, and chloranil have been studied under very high pressures. The lowest resistivity at 500 kbar is about 5 Ω-cm for hexaiodobenzene and 5 × 10−2 Ω-cm for iodanil. This difference may be mainly explained by the charge transfer from iodine to oxygen atoms in the latter compound.

Absorption spectra and photoemission of ammonium-TCNQ salt evaporated films

Abstract A vacuum deposition of ammonium tetracyanoquinodimethanide, NH 4 (TCNQ), on a glass substrate was carried out successfully. In the film deposited onto the cooled substrate, the TCNQ anion, which shows an electronic spectrum similar to that of the monomer in solution, was observed for the first time in the solid state. A preliminary result of the photoemission is also presented.