A photochromic–acidochromic HCl fluorescent probe. An unexpected chloride-directed recognition

Abstract

Non-classical protomerism of Schiff bases offers several advantages; for example, specific interactions in the -C[double bond, length as m-dash]N- linkage can be controlled and differentiated because the interactions are not governed by keto-enol tautomerism. Herein, the pH sensing properties of a new protomeric Schiff base probe () are reported. In particular, among several acids, the probe displays significant optical responses upon interaction with hydrochloric acid (HCl). X-ray structural analysis confirmed the existence of an intermolecular interaction with HCl through a -C[double bond, length as m-dash]NH-ClO- linkage. Moreover, an optical response via a second channel is manifested as photochromic fluorescence behavior. The properties of were investigated by UV-vis and fluorescence spectroscopy in a solution and the solid state. Its strong acidofluorochromic behavior was analyzed and its pKa and values were determined, which revealed a photobasic character. Positive solvatochromism that resulted from specific interactions taking place in was studied using four different solvent scales, namely, Lippert-Mataga, Kamlet-Taft, Catalán and the recently proposed scale of Laurence et al., which yielded consistent results. Finally, theoretical calculations were conducted to analyze the mechanism of the probe in terms of natural transition orbitals (NTOs) and the spatial extent of charge transfer excitations.

Controlling pH‐Sensitive Chemical Reactions Pathways with Light ‐ a Tale of Two Photobases: an Arrhenius and a Brønsted

“…[17][18][19][20][21] Several molecules have shown the capability to serve as a Brønsted photobase, consisting of mainly quinoline-based and acridine-based molecules, although several other molecules have shown this capability. [22][23][24][25][26][27] Arrhenius photobases are capable of hydroxide ion release in their electronically excited state. The most notable example of a reversible Arrhenius photobase is malachite green carbinol base (MGCB) and its water-soluble methylated derivative.…”

“…Brønsted photobases are compounds that are weak bases in their ground state; however, they become strong bases capable of proton capture in their electronically excited state [17–21] . Several molecules have shown the capability to serve as a Brønsted photobase, consisting of mainly quinoline‐based and acridine‐based molecules, although several other molecules have shown this capability [22–27] . Arrhenius photobases are capable of hydroxide ion release in their electronically excited state.…”

Ultrafast Dynamics of a “Super” Photobase

“…[11] A recent example highlights photoacids in the enantioselective protonation of silyl enol ethers leading to enantioenriched α-substituted carbonyls. [12] In contrast, the literature on photobases is scarce and limited to heterocyclic amines such as acridines, [13] 3-styrylpyridines, [14] aminoanthraquinones, [15] Schiff bases, [16] and quinolines. [17] Curcumin, [18] xanthone, [19] and other bifunctional photoacids have been sporadically reported to show certain photobasic features.…”