Shoji Fujisawa

Application of photoelectron spectroscopy to the study of photochemical reactions of solids. photooxidation of rubrene (5,6,11,12-tetraphenylnaphthacene)

Abstract Photoelectron spectroscopy was applied for the first time to the study of a photochemical reaction in solids, the reaction of a rubrene film being taken as an example. The measurement of the absorption spectrum indicates that the photo-oxidation takes place in the bulk. The change of the photoelectron spectrum shows that about 50% of the original rubrene is recovered upon heating the peroxide.

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 ).

Conformation of condensed polycyclic aromatic hydrocarbons Part III. The molecular and crystal structure of tribenzo [a,h,rst] phenanthra [1,2,10-cde] pentaphene: a simple analysis of the in-plane distortions due to overcrowding

Abstract The crystal and molecular structure of tribenzo [ a,h,rst ] phenanthra [1,2,10- cde ] pentaphene was determined by X-ray diffraction with final agreement factor R=0.057 for 2842 reflections. The molecule is largely distorted from a planar structure owing to a steric repulsion between the overcrowded hydrogen atoms. The deviations of the atoms from the mean plane of the whole molecule range from −1.78 to 1.52 A. The molecule has an approximate twofold axis perpendicular to the mean molecular plane and takes a saddle form. A simple analysis of the out-of-plane and in-plane distortions shows that the latter should not be neglected.

Synthesis of Hexabenzo[a,cd,f,j,lm,o]perylene

Hexabenzo[a,cd,f,j,lm,o]perylene (HBP), an undecacyclic condensed polycyclic aromatic hydrocarbon with two severely crowded fjord regions, was synthesized by Clars method; the starting material 8H-benzo[fg]-naphthacene-8-one was newly prepared by the glycerol condensation of 5,12-dihydro-naphthacene-5,12-dione. 1H and 13C NMR spectra of HBP were measured and the chemical shifts were completely assigned. Absorption and fluorescence spectra of HBP were also measured and the effects of nonplanarity on its spectroscopic properties was discussed.

Synthesis of Dibenzo[def,i]Naphtho[vwx-1,8,7]Pyranthrene

Abstract Dibenzo[def,i]naphtho[vwx-1,8,7]pyranthrene (12), a new dodecacyclic aromatic hydrocarbon is synthesized by the condensation reaction of a 1:1 mixture of 7H-benz[hi]chrysene-7-one (7) and 13H-dibenz[a,de]anthracene-13-one (8) with zinc dust in the presence of zinc chloride and sodium chloride. The reaction is selective and no condensation compounds of two identical ketones are produced at the 1:1 ratio; at other ratios, condensation of identical ketones (between 7 and 7, or 8 and 8) occurs. Compound 12 has a melting point of 402-403°C and a maximum absorption band at 538 nm in dichlorobenzenc, and its molecular structure is confirmed by X-ray analysis.

Phosphorescence of Large Polycyclic Aromatic Ketones

Abstract Phosphorescence measurements were performed for 6H-benzo[cd]-pyren-6-one (l), 2-nitro-benzo[hi]chrysen- 13-one (2), 2-bromo-di-benzo[a, de]anthracen- 13-one (3), and 7H-benzo[hi]chrysen-7-one (4) in an ethanol-ether-toluene mixed solution and the character of their lowest excited triplet (T1) states were investigated. The phos horescence of the compounds appears at about 5,200 – 6,000 cm−1 to the red of their fluorescence, indicating that the T, states have ππ* character. On the other hand, the short phosphorescence lifetimes, 10 – 60 ms, suggest nπ* transitions. Such a duality of the T1 state seems to be characteristic of large polycyclic aromatic ketones. The polarized emission study revealed that the duality is ascribed to strong mixing of ππ* and nπ* natures.

Absorption and Fluorescence Spectra of Nitrobenzanthrones

To identify nitrobenzanthrones (NBAs) such as 3-nitro-7 H -benz[ de ]anthracene-7-one (3-NBA) on the basis of their electronic spectral data, we have synthesized 1-, 2-, 3-, 9-, and 10-NBAs and measured their absorption and emission spectra. The first strong absorption band of the NBAs appeared in the region 350-440 nm; the band of 10-NBA was red-shifted by about 20 nm. The molar absorptivities of 3- and 9-NBA were about two times as large as those of the others. The fluorescence spectra of the NBAs varied more largely with the position of the nitro group compared to the absorption spectra. The quantum yields of fluorescence were very small, ranging from ∼10 m 2 for 2- and 10-NBA to ∼10 m 4 for 1- and 3-NBA. 3-NBA exhibited a characteristic spectrum with two broad bands at 450 and 530 nm. On excitation causing an n ~ * transition in the NBAs, their fluorescence intensities increased by a factor of 10. Phosphorescence was observed at 77 K for all compounds though that of 1-NBA was very weak. These results give the promise of characterizing individual isomers of NBAs on the basis of their spectroscopic data.

Studies of Alkali Fusion of Benzanthrone By-Producing Isoviolanthrone A

The relation between the yields of three isomers of violanthrone--violanthrone A (VOA), violanthrone B (VOB), and isoviolanthrone A (isoVOA)--and the condition of the alkali fusion of benzanthrone have been studied. When the method of alcoholic alkali fusion was applied to benzanthrone at low temperature, the major product was VOB. On the other hand, it was reported by Di Raddo et al. (2) that isoVOA was not obtained as a by-product under proper conditions (alkali fusion at high temperature) of synthesizing VOA. However, the result by the present authors is that 6 ∼ 7 percent of the A compound is isoVOA.

Structure-Reactivity Studies by NMR Spectroscopy and Molecular Orbital Calculation: Nitration of Polycyclic Aromatic Ketones

Abstract Complete assignments of NMR spectra were made for benzanthrones, using 2D correlation spectroscopic techniques of homonuclear H-H COSY and NOESY and heteronuclear CH-COSY and COLOC methods. The nitration positions for 6H-benzo[cd] pyren-6-one (1), 13H-dibenzo[a, de]anthracen-13-one (2), 7H-benzo-[hi]chrysen-7-one (3), 7H-dibenzo[a, kl]anthracen-7-one (4), 5H-benzo[fg]naphthacen-5-one (5) and 7H-benzo[de]anthracen-7-one (6) were determined on the basis of the weak or negative NOE cross peaks, which agreed with the results of the absolute values and phase sensitive 2D NOESY experiment. The nitration positions for the benzanthrones were explained by the appearance of negative or weak NOE cross peaks in the 2D NOESY spectra. Molecular orbital calculations also showed that (1), (2), (4) and (6) have the largest electron densities of the highest occupied molecular orbitals at the carbon atoms where nitration takes place. A correlation can be seen between the 2D NOESY spectra and molecular orbital calcu...

Nitration of Condensed Polycyclic Aromatic Ketones

Abstract Nitration of three isomeric dibenzanthrones, 13H-dibenzo[a,de]-anthracene-13-one(3), 7H-benzo[hi]chrysene-7-one(4), and 7H-dibenzo[a,kl]anthracene-7-one(5), with concentrated nitric acid was studied under various conditions. The nitration of (3) at 15 °C in 1,1,2,2-tetrachloroethane gave the 5-nitro derivative. The nitration of (4) in boiling acetic acid produced the 9-nitro derivative. The nitration of (5) at 70 °C in acetic acid gave the 5-nitro derivative. These nitro compounds are very useful in synthesizing undecacyclic aromatic hydrocarbons.