Effect of Electron Demand on Sensing Behavior of Carbazolopyridinophanes
Hydrazine (HZ), monomethylhydrazine (MMH), and 1,1-dimethylhydrazine (UDMH) are widely used as high energy rocket propellants in bipropellant rocket engines. However, hydrazine and its derivatives are highly flammable and carcinogenic. Currently, hydrazine sensors used for detection are irreversible which makes them costly. Two proposed carbazolopyridinophanes containing intramolecular hydrogen bonds were synthesized to detect hydrazine as real-time reversible sensors. However, their thresholds for detection (100 and 25 ppb for CPand 22OMeCPrespectively) were above the regulatory limit of 10 ppbdue to background fluorescence. It was established that the quenching of carbazole in the presence of the CP system has a direct correlation to the relative strength of the intramolecular hydrogen bond to the pyridine subunit.Our goal was to synthesize a carbazolopyridinophane with an electron donating dimethylamino group with the aim of decreasing both the background fluorescence and the detection limit. (CH3)2NCPwas synthesized and purified for photophysical studies. Butylamine was chosen as the analyte tomimic HZ without producing any toxic element for initial analysis. The absorption and emission spectra of (CH3)2NCPwere similar in morphology to those of CP and 22OMeCP.(CH3)2NCP’sbackground fluorescence was reduced to 0.7 % and its fluorescence was restored in the presence of 1 ppb n-butylamine, ethylenediamine and triethylamine as well as 4 ppb ammonia.It can be concluded that the addition of the electron donating group to the quencher of the phane decreased the background fluorescence and increased their sensitivity by improving the detection limit.