Study of Some Excited Singlet and Triplet Electronic States of Fluorene

Abstract

The absolute intensity of absorption parallel to the a and b axis of a fluorene crystal has been measured from 3000 to 2300 Å and allowed the following interpretation to be placed on the solution spectrum: The 3000-Å system of medium intensity and the stronger 2600-Å system are long-axis polarized, and a rather weak band at about 2730 Å is short-axis polarized. The onset of a stronger short-axis polarized transition above 2400 Å was observed. This analysis shows that fluorene has quite different electronic properties from phenanthrene and carbazole. The low-temperature absorption and fluorescence was entirely consistent with these electronic assignments. Vibrational analyses of the absorption and fluorescence spectra of fluorene in a polycrystalline n-heptane matrix at about 15°K are presented; intervals that formed overtones were tentatively assigned as totally symmetric fundamentals. Crystalline fluorene did not measurably phosphoresce when pure, but intense, blue phosphorescence of fluorene could be induced at about 6°K by the deliberate addition of dibenzthiophene as an impurity. A vibrational analysis of this phosphorescence revealed intervals identical with those in the fluorescence and phosphorescence of fluorene in n-heptane.

Electronic transitions of fluorene, dibenzofuran, carbazole, and dibenzothiophene: From the onset of absorption to the ionization threshold

“…1 c and d). The lowest A 1 symmetry transition in the crystal spectrum is close in energy for both polymorphs and in agreement with previous results [33,36]. In the spectrum of polymorph I the A 1 transitions can be assigned at 280 nm, 227 nm, 197 nm, 166 nm, and at around 145 nm (Fig.…”

“…As previously discussed [33,36], only A 1 symmetry transitions can be detected in the transmittance spectra of these crystals at normal incidence of light on the ab crystal face (containing the short and intermediate crystallographic axes). The correspondence between the electronic transitions of A 1 symmetry in the SRLD spectra, and the respective crystal spectra (measured with electric field vector in the ab plane of the crystals) can be seen in Figs.…”

“…Following the work by Bree and Zwarich [33], we used the transmittance spectra of thin crystals of fluorene, dibenzofuran and carbazole to assign A 1 electronic transitions in the crystal spectra of the three compounds. As previously discussed [33,36], only A 1 symmetry transitions can be detected in the transmittance spectra of these crystals at normal incidence of light on the ab crystal face (containing the short and intermediate crystallographic axes).…”

“…The two lowest experimentally detected A 1 transitions in the fluorene crystal spectra (at 280 nm and at around 220 nm) were assigned previously from studies of polarised crystal transmittance and reflectance spectra [33,36]. We have obtained spectra of two polymorphs of the fluorene crystal with the electric field vector of incident light in the ab face of the crystal (Fig.…”

The structure of fluorene (C13H10) and the fluorine–argon van der Waals complex from a high-resolution near ultraviolet spectrum

“…The rotational spectrum we observed was uniquely identified agan a-type transition. The electronic transition is, therefore, long-axis polarized, in agreement with the conclusion from the crystal spectra (12). A region of 20 GHz around the pure vibronic transition frequency vo was investigated in detail.…”