Unusual Red-Orange Emission from Rhodamine Derived Polynorbornene while Selectively Binding to Fe3+ ions in the Aqueous Environment

Norbornene based rhodamine derivative (NR) was observed as an “off-on” probe for Fe3+ion both colorimetrically and fluorimetrically in aqueous environment. NR and it’shomopolymer(PNR) were capable of detecting Fe3+ion with high selectivity and sensitivity in aqueous environment. The limit of detection (LOD) towards Fe3+ion for NR and PNR was found to be 49 nM and 19 nM, respectively. Interestingly, PNR had more efficacies for the detection of Fe3+ ions than NR which is expected due to the favourable side chain interaction due to the presence of multiple sensing motifs between the polymer chains. Sensing behaviour was thoroughly studied using spectroscopic techniques and possible mechanism was established by 1HNMR spectroscopic titration. We hypothesized that Fe3+ion induced the spirolactam ring opening of rhodamine unit due to its Lewis acid nature and preferable interacting with the N and O atoms present in NR as well as PNR.