This work reports a novel Michael addition based sensor for fluorescence detection of sulphite in river water samples.

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A novel fluorescent dye bis-(pyridin-2-yl-methyl)-(1,3,4-triphenyl-1H-pyrazolo[3,4-b]quinolin-6-ylmethyl)-amine (P1) has been synthesized and investigated by means of steady state and time-resolved fluorescence techniques. This compound acts as sensor for fluorescence detection of small inorganic cations (lithium, sodium, barium, magnesium, calcium, and zinc) in highly polar solvents such as acetonitrile. The mechanism which allows application of this compound as sensor is an electron transfer from the electron-donative part of molecule (amine) to the acceptor part (pyrazoloquinoline derivative), which is retarded upon complexation of the electro-donative part by inorganic cations. The binding constants are strongly dependent on the charge density of the analyzed cations. The 2/1 complexes of P1 with Zn++ and Mg++ cations posses large binding constants. Moreover, in the presence of these cations a significant bathochromic shift of fluorescence is observed. The most probable explanation of such behaviour is the formation of intramolecular excimer. This is partially supported by the quantum chemical calculations.

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The microwave-assisted reductive cyclization reaction with the use of triphenylphosphine as a reducing agent in the synthesis of 1H-pyrazolo[3,4-b]quinoxaline derivatives was investigated. Contrary to the conventional method of conducting the reaction, the process in the reactor takes 25 minutes with moderate yields (30-38 %). This procedure was used to obtain three new 1,3-dimethyl-1H-pyrazolo [3,4-b]quinoxaline derivatives with substituents at position 6 of different donor-acceptor character, which were used to determine the basic photophysical properties (UV-Vis absorption spectra, fluorescence emission spectra) and the quantum yields of fluorescence were appointed. The measurement results indicate the possible use of new compounds as materials for OLEDs. The conducted research brings new knowledge in the field of 1H-pyrazolo [3,4b]quinoxaline derivative systems and provides an alternative to conventional synthesis of pyrazoloquinoxalines.