Multi-branched triphenylamine-rhodamine derivatives: synthesis and fluorescent sensing for Cu2+ and Hg2+ ions.

Three multi-branched rhodamine based fluorescent probes TPARH1-3 have been designed and synthesized by incorporating the rhodamine fluorophore with triphenylamine. The probe TPARH1 displayed high sensitivity to Cu(2+) in aqueous CH3CN. The probes TPARH2 and TPARH3 showed high sensitivity towards Hg(2+) in aqueous EtOH medium as reflected by their signalling responses. The cooperative effects of multi-branched structures towards metal ions were carried out by UV-vis absorption titrations and time scanning fluorescence spectroscopic. In addition, the binding mode was proposed based on the job's plot. The absorption of probes 1-3 at 558 nm went through a maximum at a molar fraction of 0.5, indicating a 1:1 stoichiometry of the Hg(2+) to 1, 2 and 3 in the complex, respectively.