Rhodamine-azobenzene based single molecular probe for multiple ions sensing: Cu2+, Al3+, Cr3+ and its imaging in human lymphocyte cells.

A photoinduced electron transfer (PET) and chelation-enhanced fluorescence (CHEF) regulated rhodamine-azobenzene chemosensor (L) was synthesized for chemoselective detection of Al3+, Cr3+, and Cu2+ by UV-Visible absorption study whereas Al3+ and Cr3+ by fluorimetric study in EtOH-H2O solvent. L showed a clear fluorescence emission enhancement of 21 and 16 fold upon addition of Al3+ and Cr3+ due to the 1:1 host-guest complexation, respectively. This is first report on rhodamine-azobenzene based Cr3+ chemosensor. The complex formation, restricted imine isomerization, inhibition of PET (photo-induced electron transfer) process with the concomitant opening of the spirolactam ring induced a turn-on fluorescence response. The higher binding constants 6.7 × 103 M-1 and 3.8 × 103 M-1 for Al3+ and Cr3+, respectively and lower detection limits 1 × 10-6 M and 2 × 10-6 M for Al3+ and Cr3+, respectively in a buffered solution with high reversible nature describes the potential of L as an effective tool for detecting Al3+ and Cr3+ in a biological system with higher intracellular resolution. Finally, L was used to map the intracellular concentration of Al3+ and Cr3+ in human lymphocyte cells (HLCs) at physiological pH very effectively. Altogether, our findings will pave the way for designing new chemosensors for multiple analytes and those chemosensors will be effective for cell imaging study.