Title
Color Changes of a Full-Color Emissive ESIPT Fluorophore in Response to Recognition of Certain Acids and Their Conjugate Base Anions
Author
Saki Tsuchiya, Ken-ichi Sakai, Keiichi Kawano, Yuta Nakane, Takemitsu Kikuchi, Tomoyuki Akutagawa
Year
2018
Journal
Chemistry A European Journal
Abstract
2-(1,3-Benzothiazol-2-yl)-4-methoxy-6-(1,4,5-triphenyl-1Himidazol-2-yl)phenol (BTImP) is an excited-state intramolecular proton transfer (ESIPT) fluorophore, containing an acid-stimuliresponsive intramolecular hydrogen bond (H-bond) that can switch from the central phenolic proton to the imidazole (Im) or the benzothiazole (BT) ring nitrogens. Here, we demonstrate that BTImP shows full-color (red, green, blue, and white) emissions upon the addition of different concentrations of HClO4 or, with time, after the addition of HBF4. It also shows thermally dependent color changes between pink and blue via white in a narrow temperature range 25– 60 °C. 1 H- and 15N-NMR measurements suggest that, after the green fluorescent BTImP is protonated at its Im nitrogen, a conjugate base anion coordinates to the imidazolium (HIm+ ) proton, forming two types of complexes with different coordination states. One state shows a significantly Stokes-shifted red emission resulting from the ESIPT at the BT side, while the other shows a typical, Stokes-shifted blue emission, probably caused by the interactions of the anion with the phenolic proton, which break the BT-side H-bond. To form such a blue emitter, the use of BF4 – or ClO4 – is effective, while Cl– and PF6 – are not; this behavior depends on whether the anion can fit into the bidentate binding site consisting of HIm+ and phenolic hydroxyl groups.
Instrument
FP-8300
Keywords
Fluorescence, Chemical stability, Kinetics, Thermal stability, Materials