Cation–Anion Dual Sensing of a Fluorescent Quinoxalinone Derivative Using Lactam–Lactim Tautomerism

Abstract

A quinoxalinone derivative capable of lactam-lactim tautomerization was designed as a new fluorescence probe for sensing of cation (M(+) = Li(+) and Na(+)) and anion (X(-) = F(-), Cl(-), Br(-), and CH3COO(-)) in organic solvents. In THF, the minor lactam tautomer exhibited a weak fluorescence band at 425 nm with a typical Stokes shift of ∼4400 cm(-1), whereas the major lactim tautomer exhibited an intense fluorescence band at 520 nm with large Stokes shift of ∼8900 cm(-1) due to excited-state intramolecular proton transfer (ESIPT). The presence of either cations or anions was found to promote lactim-to-lactam conversion, resulting in the lowering of the ESIPT fluorescence. The lone pairs on the alkylamide oxygen and the quinoxalinone ring nitrogen of the lactam were found to bind Li(+) to form a 1:2 coordination complex, which was confirmed by single crystal X-ray structural analysis and fluorescent titrations. In addition, the N-H bond of the lactam was able to recognize anions via N-H···X hydrogen bonding interactions. Where X = F(-) or CH3COO(-), further addition of these anions caused deprotonation of the lactam to generate an anionic state, consistent with the crystal structure of the anion prepared by mixing tetrabutylammonium fluoride and the quinoxalinone derivative in THF. Dual cation-anion-sensing responses were found to depend on the ion-recognition procedure. The anionic quinoxalinone derivative and its Li(+) complex, which are formed by the addition of CH3COO(-) and Li(+), respectively, displayed different fluorescence enhancement behavior due to the two anions exchanging with each other.

Excited-state intramolecular proton-transfer (ESIPT) based fluorescence sensors and imaging agents

“…The most common ESIPT fluorophores are analogues of 2-(2 0 -hydroxyphenyl)benzimidazole (HBI), 2-(2 0 -hydroxyphenyl)benzoxazole (HBO) and 2-(2 0 -hydroxyphenyl)benzothiazole (HBT). Additional ESIPT fluorophores that have been reported include quinoline, 12 benzophenones, 13 flavones, 14 anthraquinones, 15 benzotriazoles, 16 N-salicylideneaniline, 17 and quinoxalines, 18 as illustrated in Fig. 1.…”

A highly selective fluorescent chemosensor for Mg2+ based on a diarylethene with a quinoxaline unit

“…The route of synthetic of [1‐(2‐methyl‐5‐phenyl‐3‐thienyl)‐2‐{2‐methyl‐5‐[3‐oxo‐3, 4‐dihydroquinoxaline‐2‐carbohydrazide] phenyl‐3‐thienyl} perfluorocyclopentene] ( 1O ) was shown in Scheme . In line with the previous methods, compound 5 and 6 were easily synthesized in high yield …”

Towards NIR‐Active Hydroxybenzazole (HBX)‐Based ESIPT Motifs: A Recent Research Trend

“…Thereafter a large number of molecules exhibiting ESIPT have been developed and are extensively studied. The most common ESIPT fluorophore are derivatives of benzophenones, flavones, quinolones, quinoxalines, anthraquinone, benzotriazoles, N‐salicylideneanilines, 2‐(2’‐hydroxyphenyl) benzimidazole (HBI), 2‐(2’‐hydroxyphenyl) benzoxazole (HBO) and 2‐(2’‐hydroxyphenyl) benzothiazole (HBT) (see Figure ). Among all ESIPT fluorophore, the HBX (i. e. HBI, HBO, and HBT) fluorophores are extensively investigated with both experimental and theoretical methods …”