Improving the structure of the quasi-line fluorescence spectrum of 1,12-benzperylene with ultrafast freezing

Abstract

We propose a procedure for improving the structure of quasi-line luminescence spectra of organic compounds at low temperatures. The procedure essentially involves spraying the test solution directly into liquid nitrogen, leading to ultrafast crystallization, and then collecting the polycrystalline mass. Such a procedure can be used for spectrofluorimetric analysis of the polycyclic aromatic hydrocarbon content in natural and anthropogenic media.Introduction. Polycyclic aromatic hydrocarbons (PAHs) are organic compounds whose basic structural element is the benzene ring. They are classified as pollutants which are widely distributed, toxic, and stable, and also are characterized by significant migrational activity and capability of harming the ecosystem [1]. Since the PAH concentration in natural media is rather low, they are studied by methods based on the use of the Shpol'skii effect [2,3]. These methods are sensitive, do not require a large quantity of the original mixture, and make it possible to perform the analysis rather rapidly.Vibronic spectra of polyatomic organic molecules are considerably smeared out even at low temperatures. However, as shown in [2], broadband molecular spectra take on a quasi-line structure under specially selected conditions. Good reproducibility, high resolution, distinctness of the quasi-line spectra, and the possibility of identifying tens of individual compounds in mixtures have made it possible to use the Shpol'skii effect to develop a method for determining the qualitative and quantitative composition of multicomponent systems [4]. The Shpol'skii method essentially involves obtaining quasi-line luminescence spectra of complicated organic molecules in specially selected solvents (more often in normal paraffins) when the solution is cooled down to 77 K and below. For each molecule, there are a number of solvents which are considered "suitable": the lines in the spectra are rather narrow and easily identified. Some solvents are also "unsuitable": the spectra are smeared out and their structure deteriorates.In this paper, we propose a method for improving the structure of the spectra which can be used to improve the reliability of PAH identification from quasi-line luminescence spectra.The Experiment. 1,12-benzperylene was chosen as the object of investigation because it is a very important PAH that is very widely distributed in natural and anthropogenic media [4]. The spectrofluorimetric apparatus was built on the basis of an SDMS diffraction spectrometer (with diffraction grating of 1200 lines/mm and reciprocal linear dispersion 1.2 nm/mm). Excitation was carried out using the emission of a DKSSh-150 xenon lamp with UFS-2 filter. Detection was done using an FE ′ U-36 photoelectron multiplier and a connected N-307 x-y plotter.We used two methods for freezing the organic compound. Conventional freezing was carried out in a cylindrical quartz cuvet with inner diameter 4 mm and wall thickness 0.5 mm by rapid immersion into a Dewar containing boiling nitrogen. The second method, prop...

Self-Organization of 1-Methylnaphthalene on the Surface of Artificial Snow Grains: A Combined Experimental–Computational Approach

“…A well-resolved characteristic vibrational progression of the emission spectrum (λ max = 317, 322, 328, 332, and 337 nm) of a monomer was apparent (Figure ; green line). Such line narrowing and better resolution of the emission spectra are typical for distinctly separated molecules at 77 K . Less intense emission bands at λ max ∼400 nm, apparently corresponding to stacked dimers, were also recognized.…”

“…A well-resolved characteristic vibrational progression of the emission spectrum (λ max = 317, 322, 328, 332, and 337 nm) of a monomer was apparent (Figure 4; green line). Such line narrowing and better resolution of the emission spectra are typical for distinctly separated molecules at 77 K. 118 Less intense emission bands at λ max ∼400 nm, apparently corresponding to stacked dimers, were also recognized. For the same sample, the excitation spectra, obtained by using all characteristic detection wavelengths (e.g., 322, 328, 342, 354, 392, and 412 nm), corresponded to those of the absorption spectrum (Figure 5, green and blue lines).…”