Unusual red-orange emission from rhodamine-derived polynorbornene for selective binding to Fe³⁺ions in an aqueous environment

Norbornene-based rhodamine derivative (NR) was observed as an "off-on" probe for Fe(3+)ions both colorimetrically and fluorimetrically in an aqueous environment.NRand its homopolymer (PNR) were capable of detecting Fe(3+)ions with high selectivity and sensitivity in an aqueous environment. ForNRandPNRthe limit of detection (LOD) towards Fe(3+)ions was found to be 49 nM and 19 nM, respectively, making these materials highly efficient. Most interestingly,PNRhas more efficacy towards the detection of Fe(3+)ions thanNR, which is expected due to the favorable side-chain interaction in the presence of multiple sensing motifs between the polymer chains. The sensing behavior was thoroughly studiedviaspectroscopic techniques. We hypothesized that the Fe(3+)ion was expected to induce the spirolactam ring-opening of the rhodamine unit due to its Lewis acid nature and preferable interactions with the N and O atoms present inNRas well asPNR.