Rotational selectivity of excitation and polarized fluorescence of complex molecules

Кухто, И. Н.; Поведайло, В. А.; Polubisok, S. A.; Tolkachev, V. A.

doi:10.1109/eqec.1994.698176

Proceedings of 5th European Quantum Electronics Conference

DOI: 10.1109/eqec.1994.698176

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Rotational selectivity of excitation and polarized fluorescence of complex molecules

И. Н. Кухто¹,

В. А. Поведайло²,

S. A. Polubisok³

et al.

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“…In this case, the rotational temperature corresponds to 15 K. We do not observe appreciable signs of the rotational branches in the spectrum. As follows from [15], for molecules that can be modeled by rigid tops, the shape of the rotational contour of the vibronic transition line is determined by the ratio of the principal moments of inertia I A /I B , I C /I B and the orientation of the oscillators with absorption and emission on the axes of the principal moments of the inertia for the molecule. For such a model, the Q branch is a narrow line [16], while the model allows us to compare the intensity of the Q branch only with the intensity of the Q branch for other types of tops and not with the intensities of the P and R branches of the contour.…”

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Spectral characteristics of heterocyclic compounds with a chain structure, cooled in an ultrasonic jet

Поведайло

Yakovlev

2006

J Appl Spectrosc

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the fluorescence spectra of POPOP, under conditions where the molecules were cooled in an ultrasonic helium jet. A line structure is observed in the spectra of POPOP and TOPOT; for the BPO molecules, whose configuration changes considerably during electronic excitation, vibrational structure is apparent only in the low-frequency region of the excitation spectrum, and a diffuse spectrum is recorded starting from ν 0 0 + 200 cm -1 . For all the compounds, in the spectra we recorded vibrations with frequencies up to 100 cm -1 , arising due to the flexibility of the molecular structure. The rotational contours of the lines for the electronic and vibronic transitions of the POPOP molecules (T rot = 10.5 K) and TOPOT molecules (T rot = 15 K) are structureless and bell-shaped. The degree of polarization of the fluorescence P fl for the jet-cooled POPOP molecules for excitation of vibrations along the absorption band up to 2000 cm -1 above ν 0 0 is practically constant (,8.4%) and matches P fl for high-temperature vapors.Introduction. In complex organic molecules with a chain structure, consisting of phenyl and oxazole rings linked by >C-C< single bonds, in the ground state these rings may be rotated relative to each other under the influence of electrostatic repulsion of adjacent nuclei of the ring hydrogen atoms. During electronic excitation, in such molecules substantial conformational rearrangements may occur which are manifested in the fluorescence excitation spectra as low-frequency vibrations of a phenyl group relative to the rest of the molecule. Such flexibility should affect the inertial characteristics of the molecule and consequently the shape of the rotational contour of the vibronic transition lines.Studies to date on the low-frequency vibrations and their potential energy surfaces have been conducted for a number of molecules under jet-cooling conditions: biphenyl [1], 9,9′-bianthryl [2], 9-phenylanthracene [3], 2-phenylindole [4], etc., for which the equilibrium configuration is nonplanar in the ground state while generally electronic excitation leads to a more planar structure.In this work, we have studied the effect of the flexibility of heterocyclic molecules with a chain structure on the fluorescence excitation spectra, the fluorescence spectra, the rotational contours of the bands for purely electronic and vibronic transitions, and the polarization of fluorescence for such molecules cooled in an ultrasonic jet. We have also carried out quantum chemical calculations for the structure of the molecules. As the objects of investigation, we selected 2-phenyl-5-(4-diphenylyl)oxazole (BPO), 1,4-di[2-(5-phenyloxazolyl)]benzene (POPOP), and 1,4-di[2-(5-n-tolyloxazolyl)]benzene (TOPOT), which are known as scintillators and are active media of lasers in gas and condensed phases [5].Experimental procedure. The fluorescence excitation and fluorescence spectra were measured using the spectrometric system described in [6]. The ultrasonic jet was formed by discharge of a mixture of vapor of the organic

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Spectral characteristics of heterocyclic compounds with a chain structure, cooled in an ultrasonic jet

Поведайло

Yakovlev

2006

J Appl Spectrosc

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Rotational selectivity of excitation and polarized fluorescence of complex molecules

Cited by 1 publication

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Spectral characteristics of heterocyclic compounds with a chain structure, cooled in an ultrasonic jet

Spectral characteristics of heterocyclic compounds with a chain structure, cooled in an ultrasonic jet

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