Electron-Rich Triphenylamine-Based Sensors for Picric Acid Detection

This paper demonstrates the role
of solvent in selectivity and
sensitivity of a series of electron-rich compounds for the detection
of trace amounts of picric acid. Two new electron-rich fluorescent
esters (6, 7) containing a triphenylamine
backbone as well as their analogous carboxylic acids (8, 9) have been synthesized and characterized. Fluorescent
triphenylamine coupled with an ethynyl moiety constitutes π-electron-rich
selective and sensitive probes for electron-deficient picric acid
(PA). In solution, the high sensitivity of all the sensors toward
PA can be attributed to a combined effect of the ground-state charge-transfer
complex formation and resonance energy transfer between the sensor
and analyte. The acids 8 and 9 also showed
enhanced sensitivity for nitroaromatics in the solid state, and their
enhanced sensitivity could be attributed to exciton migration due
to close proximity of the neighboring acid molecules, as evident from
the X-ray diffraction study. The compounds were found to be quite
sensitive for the detection of trace amount of nitroaromatics in solution,
solid, and contact mode.