A Highly Water-Soluble Fluorescent and Colorimetric pH Probe

Abstract

A new 5-(4-((2-(benzothiazole-2-carbonyl)hydrazono)methyl)-3-hydroxyphenoxy)-N,N,N-trimethylpentan-1-aminium bromide (BTABr) fluorescent and colorimetric pH probe was easily synthesized by the condensation reaction of benzothiazole-2-carbohydrazide with 5-(4-formyl-3-hydroxyphenoxy)-N,N,N-trimethylpentan-1-aminium bromide. The benzothiazole moiety provided the emissive part of the molecule and the charged trimethyl amino group guaranteed outstanding solubility in water, for an organic molecule. pH titration experiments indicated that the probe is useful for monitoring acidic and alkaline solutions, turning reversibly in color/fluorescence just at a neutral pH value. Naked-eye colorimetric response was observed both in solution and in the solid state. In addition, the probe showed high stability and selectivity and large Stokes shifts. Because of these features, BTABr can potentially work as an on-off real-time pH sensor for intracellular pH imaging. The crystal structure of BTABr examined by single-crystal analysis showed a planar geometry of the molecule and confirmed the presence of a molecular stacking between molecules joined in a complex tridimensional hydrogen bonding pattern.

A Water Soluble 2-Phenyl-5-(pyridin-3-yl)-1,3,4-oxadiazole Based Probe: Antimicrobial Activity and Colorimetric/Fluorescence pH Response

“…Compared to its precursor 5-nitro-2-(5-(pyridin-3-yl)-1,3,4-oxadiazol-2-yl)phenol, C1 is soluble and emissive in water. As expected [ 70 ], the chain increases the affinity for water. It makes the molecule fluorescent due to the implemented emission related to the electrostatic repulsions between the cationic chains [ 71 , 72 , 73 ].…”

“…Stock solutions (1.00 M) of Britton–Robinson buffer (at 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, 6.0, 6.5, 7.0, 7.5, 8.0, 8.5, 9.0, 9.5, 10.0 pH value) were prepared in bidistilled water as described in the literature [ 70 , 95 ]. Aqueous solutions of C1 1.00 mM from bidistilled water were prepared for fluorescence and absorbance titrations.…”

Visual pH Sensors: From a Chemical Perspective to New Bioengineered Materials

“…Sensing ability based on small water-soluble, simple, and organic molecules attracts researchers’ interest [ 45 , 46 ]. By adding on the sensor’s core a flexible five methylene groups branch bearing a charged trimethylammonium bromide group (box 3) B. Panunzi and coworkers developed two water soluble sensors, while preserving their organic phase solubility.…”

Zinc (II) and AIEgens: The “Clip Approach” for a Novel Fluorophore Family. A Review

“…Other significant applications of AIEgens are fluorescence chemosensors and multiple-stimuli (such as pH, electromagnetic radiation, morphology) responsive materials [ 53 , 54 , 55 , 56 ]. AIEgens can be utilised as fluorescent indicators/markers to characterise supramolecular interactions and macromolecular motions in the solid state, in an aggregate gel phase or even in a water-concentrated solution.…”