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.

Signaling preferences of substituted pyrrole coupled six-membered rhodamine spirocyclic probes for Hg(2+) ion detection.

Two six-membered spirocyclic rhodamine derivatives containing substituted pyrroles (1 and 2) were shown to exhibit preferential dual mode 'turn-on' signaling responses in the presence of Hg(2+) ions through complexation mediated spiro-ring opening. Although the rate of spiro-ring opening mediated through complexation is much slower in these probes in comparison to their five membered analogues, they exhibited a comparable sensitivity in metal ion detection.

Preferences of rhodamine coupled (aminoalkyl)-piperazine probes towards Hg(II) ion and their FRET mediated signaling.

The metal ion induced absorption and emission signaling pattern of rhodamine coupled bis-(aminopropyl)-piperazine (1-3) and (aminoethyl)-piperazine (4) based probes evaluated in MeCN as well as in an MeCN-H2O binary mixture medium revealed that these probes exhibit optical signaling perturbations to a varying extent in MeCN, however, their complexation induced signaling could be tuned selectively towards Hg(II) in the presence of an aqueous component in the solvent medium where competitive interactions such as metal-probe interactions and hydration of metal ions play the determining factor to induce aqueous promoted Hg(II) selectivity. Attachment of another fluorophore (anthracene and nitrobenzofurazan moieties in 2 and 3 respectively) at the other end of the rhodamine coupled bis-(aminopropyl)-piperazine receptor enabled these probes to facilitate a complexation induced fluorescence resonance energy transfer (FRET) from the excited fluorophore to the ring-opened rhodamine along with contributions through operative PET inhibition and rhodamine delactonization processes. The enhancement in absorption transition of these probes at ~557 nm upon selective Hg(II)-complexation and consequent colourless to pink colour change in the solution imply a chromogenic signaling pattern whereas simultaneous fluorescence amplification and/or FRET initiation lead to fluorogenic signaling to facilitate detection at lower concentration.

Alteration of selectivity in rhodamine based probes for Fe(III) and Hg(II) ion induced dual mode signalling responses.

The probes for metal ion induced chromo- and fluorogenic signalling responses alter their selectivity depending upon the nature of substituent as well as a function of solvent medium. 2 has shown selectivity towards Fe(III) ion, 4 towards Hg(II) ion while 3 is responsive towards both Fe(III) and Hg(II) ions.