Synthesis And Optical Properties Of Novel Piperazine Derivatives

Over the last two decades, much attention has been paid to the design, synthesis and characterization of fluorescent molecular sensor because of the demand in analytical chemistry, biomedical, biotechnology, the environment, etc. Biochemical processes frequently involve protonation and deprotonation of biomolecules with concomitant changes in the pH of the medium, therefore there have been many reports regarding pH probe using the fluorescent changes as a means of detection.Novel piperazine derivatives were synthesized and the three new compounds were characterized using the following means, mass spectrometry (MS), nuclear magnetic resonance (NMR) and single crystal X-ray diffraction analysis. Luminescence properties were characterized. The two new compounds produce intensive blue light under excitation of UV light in water/DMF (4:1, V/V). The increase of solution acidity results in a very important changes of spectral properties of two new compounds, the emission peak intensity of compound 4 and 6 decrease by 90%, so they can be used as pH sensor. The fluorescence decrease is based on the protonation of N-atoms, the conjugation extent of compounds decrease, and such protonation leads to the fluorescence quenching. The evolution of the fluorescence spectra versus pH is similar to that of the absorption spectra, which suggests absence of proton transfer in the excited state.