Effect of functional -NH2 groups on sensitization of 3,6-diaminocarbazole towards Picric Acid

Due to the significance of explosive detection for homeland security and environmental protection, the research of new materials and methodologies for sensing electron-deficient explosive nitroaromatics is urgently imperative. In this paper we demonstrate an opto-chemical sensor for explosive detection by using a carbazole derivative, namely 3,6-diaminocarbazole (DAC) (Φ_f=49%), was synthesized through controlled nitration of the carbazole (Φ_f=42%) with fuming nitric acid. As a proof of concept, electron-deficient explosive molecule 2,4,6-trinitrophenol (TNP) is used as a model analyte to our sensor with LOD 3.7µM. In solution, PL signal from highly electron-rich DAC gets quenched upon addition of aliquots of TNP caused by photo-induced electron and resonance energy transfer i.e. quantified by Stern-Volmer constant (KS_V= 4.1×10⁴ M^-1) which is higher than KS_V=3.3×10⁴ M^-1_,valuated for carbazole. The quenching mechanism was further established by time-resolved PL and steady state absorption spectroscopy which was found to be a mixture of static and dynamic in nature as lifetime of DAC (2.18 ns) is reduced to 1.24 ns for TNP. As a conclusion, results indicate that major response of this sensitivity enhancement to TNP originates from Föster Resonance Energy Transfer between DAC and TNP