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.
Highlights
The design of pH-responsive molecules is a remarkable field of research, finding applications in environmental, biochemical, electrochemical, and analytical technologies [1,2]
Typical fluorescence pH sensors are based on photoinduced electron transfer (PET), intramolecular charge transfer (ICT), and electron transfer (ET) effect
We explored the potential of ainvolving benzothiazole moiety, one of the most widely effect of the heterocycle on the spectroscopic response pH determination
Summary
The design of pH-responsive molecules is a remarkable field of research, finding applications in environmental, biochemical, electrochemical, and analytical technologies [1,2]. Schiff-base-containing molecules are excellent candidates to promote color/fluorescence response depending on protonation and deprotonation. We explored the potential of ainvolving benzothiazole moiety, one of the most widely effect of the heterocycle on the spectroscopic response pH determination. A new highlyone water-soluble, 5-(4-((2the present work, we explored the potential of a benzothiazole moiety, of the most widely (benzothiazole-2-carbonyl)hydrazono)methyl)-3-hydroxyphenoxy)-N,N,N-trimethylpentan-1-aminium known heterocycles, in the production of an optical pH sensor. A new highly water-soluble, 5-(4-((2bromide (BTABr) fluorescent and colorimetric probe was obtained by condensation reaction (benzothiazole-2-carbonyl)hydrazono)methyl)-3-hydroxyphenoxy)-N,N,N-trimethylpentan-1(see. B of obtained the sensor two aminium (BTABr) fluorescent and colorimetric probe form was by undergoes condensation deprotonation steps, turning to keto-enolic forms C and D, respectively, parameter. X-ray analysis of the BTABr and probe absorption and emission titrations in the pH range of 2.0–11.0.
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