Abstract:
Chemosensors for selective and sensitive detection of analytes were developed following various structural, functional and operational design methodologies. The interaction between probe and analyte has been vital in chemosensor-based detection technologies. A pertinent question in such a system is to be convincingly addressed, that if the probes incorporating spatially-positioned multiple interaction sites offer preferences towards analyte binding for a favourable and optimal interaction. The derivatized Rhodamine based probe 1 exhibiting protoninduced dual mode signalling here contained several protonation sites. The absorption and fluorescence signal enhancement on protonation of the probe attributed to its proton-mediated spiro-ring opening. Out of several plausible conformations of protonated probe [1.H+], their DFT calculations revealed the proton binding preferentially to the N-donor atom on spiro-ring of 1 instead at other probable sites of protonation such as other hetero- donor atoms on the xanthene core or the carbonyl O- atom on the spiro-ring as the energetically favourable conformation. It was verified with the protonated probe complex's X-ray diffracted single crystal structure.