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A Study of the spectra of some organic compounds Zwarich, Ronald James

Abstract

The fundamental vibrations of carbazole have been assigned from polarized infrared, Raman and fluorescence spectra. A crude normal coordinate calculation using a force field transferred from phenanthrene for the in-plane problem, and from benzene and anthracene for the out-of-plane problem gave satisfactory agreement with the observed frequencies. From a study of the polarized absorption spectrum of carbazole in a single crystal matrix of fluorene at about 15°K, the lowest-energy transition is assigned ¹A₁←¹A₁, and the excited state vibrations are analysed. In fluorene, an impurity with a weak absorption at 3200 Å, which previous workers inadvertently attributed to fluorene itself, was characterized as benz[f] indan. From the polarized absorption and fluorescence spectra, the transition is assigned ¹A₁←¹A₁ and vibrational analyses of these spectra are given. From a study of the absorption spectrum of a-fluorene crystal (ab face), the solution absorption spectrum is given the following interpretation: the 3000 Å system of medium intensity and the stronger 2600 Å system are long-axis polarized, and a rather weak band at 2730 Å is short-axis polarized. Vibrational analyses of the absorption and fluorescence spectra in a polycrystalline n-heptane matrix at about 15°K are presented. A vibrational analysis of the intense blue phosphorescence induced in fluorene by the deliberate addition of dibenzothiophene at about 6°K shows that the intervals are identical with those in the fluorescence and phosphorescence of fluorene in n-heptane. An assignment of the fundamentals of fluorene from polarized infrared and Raman spectra is reported. Polarized infrared and Raman spectra of dibenzothiophene-h₈ and -d₈. are utilized in an assignment of their fundamental vibrations. The in-plane frequencies were calculated using the force field transferred from phenan-threne. The lowest-energy transition of dibenzothiophene in fluorene at about 15°K is assigned ¹A₁←¹A₁. Vibrational analyses of the absorption spectrum in n-heptane and of the fluorescence and phosphorescence spectra in the crystal, n-heptane, and hexamethylbenzene are presented. An intense blue phosphorescence observed at 6°K in a biphenyl crystal following the deliberate addition of either carbazole or dibenzothiophene was identified as biphenyl phosphorescence originating from energy trapping centers created in the crystal lattice. The triplet band energy of biphenyl estimated from preliminary temperature dependence studies of the phosphorescence and delayed fluorescence agrees satisfactorily with Hirota's independent measurement.

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