The dissertation describes the synthesis and determination of photophysical characteristics of some new derivatives of 1,3,5-triaryl-(hetaryl)-2-pyrazoline and 3- hydroxychromone aiming to elucidate the possibility of their application as fluorescent probes and chemosensory compounds. The use of organic derivatives for the qualitative and quantitative detection of analytes of various nature, as well as for monitoring biological processes at molecular level, which is based on the principle of changing fluorescence parameters of the probe molecule under the influence of its close surrounding (as it is also called “fluorescence switching”). Despite the huge number of already known sensor compounds, designing of new ones and chemical modification of existing classes of fluorescent probes with the aim of improving their sensitivity and expanding the scope of practical application, as well as detecting their photophysical characteristics, remain an urgent task of modern synthetic organic and physico-organic chemistry.
During the dissertation investigation, a number of new 1,3,5-triaryl-(hetaryl)- 2-pyrazoline derivatives were synthesized for the first time, namely: 1-(2-pyridyl)- 3,5-diphenyl-2-pyrazoline, 1-(2-pyridyl )-3-(2-hydroxyphenyl)-5-phenyl-2- pyrazoline, 1-(8-hydroxyquinolyl)-3,5-diphenyl-2-pyrazoline, 1-(8- hydroxyquinolyl)-3-(2-hydroxyphenyl )-5-phenyl-2-pyrazoline, 1-(2-pyridyl)-3-(2- benzthiazolyl)-5-phenyl-2-pyrazoline, 1-(2-pyridyl)-3-(2-benzimidazolyl)- 5- phenyl-2-pyrazoline. Also, a representative of 3-hydroxychromone series was synthesized for the first time: 2-(1-ethyl-1H-benzimidazol-2-yl)-3-hydroxy-4Hchromen-4-one.
The spectral and photophysical characteristics of the synthesized pyrazoline derivatives were determined in a series of solvents of different polarity and proton donor ability. The position of the long-wavelength absorption band of 1-(2-pyridyl)- 3,5-diphenyl-2-pyrazoline practically does not depend on the physical and chemical characteristics of the solvent, which indicates quite low dipole moment of this compound in the ground state. At the same time, the position of the fluorescence spectrum is sufficiently regulated by the nature of the solvent. The dependence of the Stokes shift on the solvent polarity function demonstrated good linearity: the data for proton donor methanol did not fall out of the general plot. Similar behavior was also demonstrated by 1-(8-hydroxyquinolyl)-3,5-diphenyl-2-pyrazoline. The absence of additional emission bands in the fluorescence spectrum of the latter compound indicated the absence of proton phototransfer reaction, despite the presence of an intramolecular hydrogen bond in the 8-hydroxyquinoline moiety.
The study of electronic absorption spectra, fluorescence and photophysics of 2-(1-ethyl-1H-benzo[d]imidazol-2-yl)-3-hydroxy-4H-chromen-4-one was carried out in a series of solvents of different polarity: aprotic hexane, 1,2-dichloroethane, tetrahydrofuran, acetonitrile and protic ethanol. The fine vibrational structure of the long-wavelength absorption band in hexane was clearly observed. This feature remained almost unchanged in polar/protic solvents. As in the case of other compounds of the flavonol family, two well-separated fluorescence bands, belonging to the normal and phototautomer forms, were registered experimentally. High quantum yields of ~0.5 are typical for the discussed compound in an environment of low-to-medium polarity. In polar and especially in protic solvents, a tendency to decrease the overall fluorescence efficiency was elucidated. In all the investigated solvents, the excited state proton transfer reaction proceeds quite efficiently with a rate constant of approximately 1011 s-1. Here we came to conclusion, that the fast proton phototransfer reaction in this case plays the role of a factor of increasing of the total fluorescence quantum yield. The decrease in quantum yield in polar aprotic solvents can be explained by a certain deceleration of the excited state proton transfer reaction in polar environment.
Practical significance of the obtained results: the synthesized derivatives of 1,3,5-triaryl-2-pyrazoline, taking into account their spectral characteristics and the ability to form complexes with double-charged metal cations, can be used in the spectrophotometric and/or spectrofluorimetric detection of heavy metals-toxicants in environmental analysis. The sensitivity of the synthesized pyrazoline derivatives to cadmium ions is sufficiently high (the formed complexes are not destroyed by addition of Trilon B to their solutions) and is at the level of the best representatives of fluorescent chemosensory compounds for cadmium. The studied derivatives of 3- hydroxychromone, due to their high sensitivity to the nature solvent, can be used as probes for estimation of the physical-chemical parameters of the environment.
