Tripodal Fluorescent Sensor for Encapsulation-Based Detection of Picric Acid in Water

The combination of steric gearing in substituted triethylbenzene and linear structures of 1-(4-biphenyl)(benz)imidazolium moieties have been used to design and synthesize tripodal chemosensors with preorganized cavities for detection of picric acid (PA) in (4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES) buffer. The two chemosensors undergo highly selective fluorescence quenching with PA and lead an ap-proximate tenfold increase in K-SV values (3.57 x 10(5)m(-1) and 2.67 x 10(5)m(-1)) and greater than 2000 times higher sensitivity than earlier reported benzimidazolium-based chemosensors. The upfield shift of PA protons (Delta delta approximate to 0.8) in H-1 NMR titration studies reveals encapsulation of PA in the cavity of the sensors. In water, one of the sensors can detect 1.0 nm PA as the lowest detection limit and TLC strips doped with the same sensor can detect 137 agcm(-2) of PA under UV illumination. Thin films of this sensor undergo fluorescence quenching in the presence of PA vapor in less than 120 seconds.