Signalling probes appended with two rhodamine derivatives: inter-component preferences, Fe(III)-ion selective fluorescence responses and bio-imaging in plant species

Abstract

The photophysical investigation of two amino-alkyl receptor-based probes, 1 and 2, appended with two different rhodamine derivatives but differing in their receptor constituents revealed their selective absorption and fluorescence signalling responses to Fe(III) among all metal ions investigated. Although the output channels in the complexation-induced signalling patterns of these probes are in proximity to each other, the spectroscopic signatures of Fe(III)-complexation spiro-ring opening of the individual rhodamine derivatives and associated kinetic measurements revealed a preferential coordination affinity of the rhodamine 6G (Rho-6G) component over the rhodamine-B (Rho-B) segment. The Fe(III)-selective signalling response was observed to be higher in flexible DETA(bis(2-aminoethyl) amine) receptor-incorporated probe 1 than in 2, which incorporates a rigid ethylenediamine receptor. The ratio of the fluorescence of the two wavelength output channels arising from the two different signalling subunits in the architectures of these probes enhances their sensitivity levels in Fe(III) ion detection. The utility of the Fe(III)-complexation-induced orange fluorescence output of 1 was demonstrated in the detection and localization of bio-accumulated Fe(III) ions in root tissues of Grevillea pteridifolia plant species.