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Synthesis, Characterization and Evaluation of Fluorimetric Chemosensors for Ions Based on Diphenylimidazole Derivatives
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1  Centro de Quimica, Universidade do Minho

Abstract: Chemosensors are a subject of great interest and in recent years great efforts have been made to develop fluorescent probes that are capable of detecting ions with high sensitivity and selectivity. The ideal fluorophore for chemosensory application should have high fluorescence quantum yield, high molar extinction coefficients, long-wavelengths of excitation and emission, long service life and high photostability.[1]The imidazole nucleus plays an important role in medicinal chemistry and in biochemical processes as structural component of several biomolecules and has varied pharmacological activities.[2] Earlier studies reported by us showed that the optical and thermal properties of imidazole derivatives could be tuned by substitution of aryl groups at positions 2, 4 and 5 by five-membered heterocycles giving rise to innovative applications of these p-conjugated systems in nonlinear optics, chemosensors and DNA intercalators.[3]In this communication, we report the synthesis of new diphenylimidazoles in order to evaluate their photophysical properties and chemosensory ability. Therefore, imidazole derivative 2 bearing an heterocyclic π-bridge as well as the corresponding N-alkylated compound 3 were obtained in good yields through a Radziszewski reaction. The new derivatives were characterized by the usual techniques and a detailed photophysical study was undertaken. The evaluation of the compounds as fluorimetric chemosensors was carried out by performing spectrofluorimetric titrations in acetonitrile in the presence of relevant organic and inorganic anions, and of alkaline, alkaline-earth and transition metal cations.  Acknowledgements: Thank are due to Fundação para a Ciência e Tecnologia (Portugal) and FEDER-COMPETE for financial support through Centro de Química (PEst-C/QUI/UI0686/2013 (FCOMP-01-0124-FEDER-037302)) and Centro de Física [PTDC/CTM/105597/2008 (FCOMP-01-0124-FEDER-009457)], and a PhD grant to R.C.M. Ferreira (SFRH/BD/86408/2012). The NMR spectrometer Bruker Avance III 400 is part of the National NMR Network and was purchased with funds from FCT and FEDER. We are also grateful to the Instituto da Educação of Universidade do Minho for providing the laboratory infrastructure necessary for the development of this work.  References:1. Martinez-Mãnez R.; Sancennon, F. Chem. Rev. 2003,103, 4419.2 a) Rani N.; Sharma A.; Gupta G.K.; Singh R. Mini-rev. Med. Chem. 2013, 13, 1626.  b) Bellina F.; Cauteruccio S.; Rossi R. Tetrahedron 2007, 63, 4571. 3 a) Batista R. M. F.; Costa S. P. G.; Belsley M.; Lodeiro C.; Raposo M. M. M. Tetrahedron 2008, 64, 9230. b) Pedras B.; Batista R. M. F.; Tormo L.; Costa S. P. G.; Raposo M. M. M.; Orellana G.; Capelo J. L.; Lodeiro C. Inorg. Chim. Acta 2012, 381, 95. c) Batista R. M. F.; Costa S. P. G.; Raposo M. M. M. J. Photochem. Photobiol. Chem. 2013, 259, 33.
Keywords: Chemosensors; Diphenylimidazole; Imidazole derivatives; Fluorescence