Two-step FRET mediated metal ion induced signalling responses in a probe appended with three fluorophores.

A tri-fluorophoric molecular probe (1) with three different derivatized fluorophores, i.e. anthracene (An), 7-nitrobenz-2-oxa-1,3-diazole (NBD) and rhodamine-B (Rh) appended on to a Tren [tris-(2-aminoethyl)amine] receptor was demonstrated to exhibit metal ion induced ratiometric fluorescence signalling through the initiation of a two-step fluorescence resonance energy transfer (FRET) process owing to a compatible and substantial spectral overlap of electronic absorption and fluorescence of initial donor-intermediate donor/acceptor-final acceptor pairs. The steady-state and time-resolved fluorescence spectral investigation of probes (1a-1f) with individual excitation energy donor (D)/acceptor (A) fluorophores as well as different bi-fluorophoric D-A pairs appended to the same receptor, and comparison with those of 1 revealed a higher energy transfer efficiency between the initial donor (F