Influence of Urea N–H Acidity on Receptor–Anionic and Neutral Analyte Binding in a Ruthenium(II)–Polypyridyl-Based Colorimetric Sensor



A new ruthenium(II)–polypyridyl complex {[Ru(bpy)2L]2+; bpy = 2,2′-bipyridyl, L = 1-(6-nitro-1,10-phenanthrolin-5-yl)-3-phenylurea} having a urea functionality as a receptor fragment for anionic analytes was synthesized. Its binding affinity towards various oxy anions and halides was studied. This complex was found to act as a selective colorimetric sensor for F among halides and CH3COO/H2PO4 among oxy anions. The relative binding affinity of different anions towards this receptor was examined by using quantum chemical calculations. This complex was also found to act as a colorimetric sensor for neutral molecules like DMSO and DMF, though the binding affinity was weaker than that of the three anions mentioned above. The relative acidity of two HNurea atoms was compared with that of one from the related complex by using pKa calculations, and its influence on binding affinities towards different analytes is discussed. Results of the time-resolved fluorescence studies reveal that two nonequilibrated excited states exist involving two different 3MLCT transitions, namely Rudπ → bpyπ* and RudπLπ*.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)