Towards the development of controllable and reversible ‘on-off’ luminescence switching in soft-matter; synthesis and spectroscopic investigation of 1,8-naphthalimide-based PET (photoinduced electron transfer) chemosensors for pH in water-permeable hydrogels

Abstract

The synthesis of the pH PET sensors 1 and 2 is described. These molecules display 'on-off' switching in their fluorescence as a function of pH in aqueous solution. From the luminescent changes pK a values of 8.4(±0.1) and 6.3(±0.1) were determined respectively. These compounds were incorporated into poly[methylmethacrylate-co-2-(hydroxyethylmethacrylate)]-based hydrogels and the luminescent properties of the resulting polymeric films were investigated using confocal laser-scanning microscopy. Both sensors showed substantial luminescent switching in the soft-matter, where the emission was 'switched off' after treating the hydrogels with alkaline solution and 'switched on' under acidic conditions.

Colorimetric and fluorescent anion sensors: an overview of recent developments in the use of 1,8-naphthalimide-based chemosensors

“…40 Many other examples of such pH dependent PET naphthalimide sensors have been developed to date, for use in solution or within, or on, solid supports. 18 In contrast, compound 3, possessing a crown ether receptor was developed for analysis of Na + in blood samples, 41 while 4 42 and 5 43 have been developed for detecting Zn(II). Structure 4 has also recently been used for imaging of bone structures using epifluorescence microscopy.…”

“…Consequently, the 1,8-naphthalimide structure has been extensively used within the dye industry, as strongly absorbing and colourful dyes, in the construction of novel therapeutics, 16 as well as in the formation of chemical probes, [17][18][19][20] particularly for the sensing of biologically relevant cations. [21][22][23] It is thus no surprise that this structure has found application in the field of anion recognition and sensing, and in the last seven years or so many excellent examples of naphthalimide-based anion sensors have been published, clearly demonstrating the versatility of this structure within this fast growing field of research.…”

Synthesis of 1,8-naphthalimide-based probes with fluorescent switch triggered by flufenamic acid

“…The optical and photophysical properties of 1,8-naphthalimides are very sensitive to any changes in the chemical structure of the aromatic ring via the addition of substituents [12,13]. In particular, the introduction of amines to the 1,8-naphthalic-anhydride core has been extensively explored because the proton input results in alteration of fluorescence properties [14,15]. In addition to chemical modifications, the emission spectra of many fluorophores are sensitive to the polarity of the surrounding environment (solvent effects) [8,11,14].…”

Optical probes for the detection of protons, and alkali and alkaline earth metal cations

“…Gunnlaugsson's 10 also operates according to the PET mechanism and possesses either a piperidine (10a) or morpholine (10b) receptor to modify the pK a value. 17 The probes where then incorporated within a mixed poly(methylmethacrylate) (MMA) poly(hydroxyethylmethacrylate) (HEMA) hydrogel. The resulting hydrogels were shown to be responsive to pH with a significant enhancement in fluorescence when they were bathed at pH 2.5 compared to 11.5.…”