One-pot synthesis of a new rhodamine-based dually-responsive pH sensor and its application to bioimaging

Photophysical investigations of a FRET-based bifluorophoric conjugate and its Hg(II) specific ratiometric ‘turn-on’ signalling

“…The synthesis of compound L2 was reported [31] recently through one-pot methodology, however, obtained here following a step-wise synthetic approach. To a stirring solution of L1 …”

“…Such ratiometric mode of signalling pattern determines analyte concentrations as a function of ratio of donor and acceptor emission intensities and facilitates the probe's efficiency for a much lower detection level avoiding associated signal-to-noise interferences. Although the probe L2 was reported [31] recently as pH sensor under different operating conditions (2.46 pH), the signalling module involving operative photophysical processes and their proton induced perturbation to result in observed spectroscopic changes is still illusive as the probe consist of two discrete protonation sites (recognition port) in form of two donor amino groups in the receptor unit, therefore, restricted quantification of extent of FRET upon simultaneous protonation. Similar protonation induced spectroscopic signals are also anticipated in probes those consist of same fluorophore pair but a different receptor unit incorporating provision for two discrete metal ion coordination.…”

“…Its subsequent aromatic nucleophilic substitution reaction(SN2) with 4-chloro-7-nitro-benz-2-oxa-1,3-diazole afforded L2 as the desired probe. It was recently reported[31] as a pH sensor with operational pH at 2.46; however, photophysical processes such as FRET modulation, extent of energy transfer and solvatochromic effects were not elaborately investigated. The reference compound was synthesized by condensation of freshly prepared N-[2-(1-piperazinyl)ethyl] benzamide (L3a) with 4-chloro-7-nitro-benz-2-oxa-1,3-diazole(Cl-NBD).…”

An easily Prepared Fluorescent pH Probe Based on Dansyl

“…To date, a large variety of fluorescent pH probes were fabricated successfully based on rhodamine [13][14][15][16], naphthalimide [17,18], coumarin [19,20], dansyl [21,22] and fluorescein [9]. Most of the rhodamine-based, naphthalimide-based and coumarin-based pH probes exhibited Bacid on-alkali off^behavior and some of them could only be lighted up by strong acidity [13,15].…”

“…Most of the rhodamine-based, naphthalimide-based and coumarin-based pH probes exhibited Bacid on-alkali off^behavior and some of them could only be lighted up by strong acidity [13,15]. The fluorescent pH probes acted as Balkali on-acid off^are relatively scarce and greatly demanded.…”