Derivatives of 1,3,5 triaryl-2-pyrazoline with additional heterocyclic moieties in position 1 as potential fluorescent chemosensing compounds for detection of polyvalent metals cations

A series of 1,3,5-triaryl-2-pyrazoline derivatives with pyridine or 8'-hydroxyquinoline fragments in position 1 have been synthesized, some of which also contain a hydroxy group in the ortho-position of benzene ring-3, which makes possible the their OH-group proton phototransfer reaction to the nitrogen atom of pyrazoline cycle. The nitrogen atoms in molecules of the investigated compounds form chelate cavities, binding of the ions of polyvalent metals to which should lead to changes in the spectral characteristics. The spectral-luminescent properties of the synthesized compounds in solvents of different polarity and their interaction with salts of several polyvalent metals in acetonitrile were investigated. The proton phototransfer reaction was shown to result in significant fluorescence quenching, the most prominent for the derivative with the hydroxyquinoline fragment in position 1 of pyrazoline cycle. The proton transfer reaction rate constants vary within the interval of 2-4∙109 s-1 in aprotic solvents of different polarity. The prospects for application of the synthesized derivatives as fluorescent chemosensor compounds for the analysis of polyvalent metals were examined. In most of the studied cases, their interaction with heavy metal ions led to decrease of fluorescence intensity, however for compounds with intramolecular proton phototransfer reaction, no significant quenching by heavy metal ions was observed. The exception was the mercury ions, in the interaction with which compounds with proton phototransfer reaction demonstrated intensity redistribution of their two emission bands on the background of their general fluorescence quenching. The latter circumstance indicates the possibility of application of the modern methods of ratiometric fluorescence detection for the analysis of Hg2+ ions with their help.

2-(benzimidazol-2-yl)-3-hydroxychromone derivatives: spectroscopic properties and a possibile alternative intramolecular proton phototransfer

Three 2-(benzimidazol-2-yl)-3-hydroxychromone derivatives were synthesized. Their spectroscopic and fluorescent properties, due to excited state intramolecular proton transfer (ESIPT) from OH to carbonyl, were studied. Theoretical possibility of an alternative intramolecular H-bonding and experimental evidence for such behavior are discussed.