Colorimetric and Ratiometric Fluorescence Sensing of Fluoride:  Tuning Selectivity in Proton Transfer

• Published in: Journal of organic chemistry 2005-12, Vol.70 (25), p.10524-10531
• Main Authors: Peng, Xiaojun, Wu, Yunkou, Fan, Jiangli, Tian, Maozhong, Han, Keli
• Format: Article
• Language: English
• Subjects: Chemistry; Exact sciences and technology; Heterocyclic compounds; Heterocyclic compounds with several n hetero atoms in the same ring, in separated rings or in fused rings; Organic chemistry; Preparations and properties
• ISSN: 0022-3263; 1520-6904
• DOI: 10.1021/jo051766q

Phenyl-1H-anthra[1,2-d]imidazole-6,11-dione (1) and its derivatives (2 and 3) have been investigated as new colorimetric and ratiometric fluorescent chemosensors for fluoride. Acute spectral responses of 1 and 3 to fluoride in acetonitrile have been observed:  an approximately 100 nm red shift in absorption and fluorescence emission and a very large ratiometric fluorescent response (R max/R min is 88 for sensor 1 and 548 for sensor 3). From the changes in the absorption, fluorescence, and 1H NMR titration spectra, proton-transfer mechanisms have been deduced. In ground states, a two-step process has been observed:  first, the formation of the sensor-fluoride hydrogen-bond complex [LH···F]- and then the fluoride-induced deprotonation of the complex to form L- and FHF-. In excited states, the excited-state intermolecular proton-transfer made a contribution to the deprotonation. The selectivity for F- can be tuned by electron push−pull properties of the substituents on the phenyl para position of the sensors. Sensor 1 shows the best selectivity. The excellent selectivity of 1 for F- is attributed to the fitness in the acidity of its NH-group, which is tuned to be able to distinguish the subtle difference in the affinity of F-, CH3CO2 -, and H2PO4 - to proton.