New Pyrazoline Derivatives as “off-on-off” Fluorescent pH Sensors
Design of new optical pH sensors is a remarkable field of research due to its important functions in many are as such as environmental, biochemical, electrochemical and analytical [1,2]. Fluorescent pH sensors have superior properties such as high sensitivity, high se- lectivity, fast response and lowcost compared to other methods such as acid–base indicator itration  and potention metrict itration . Fluore scence pH sensors respond top H changes either “on-off (oroff- on)” or “off-on-off (or on-off-on)”. Pyrazoline derivatives, typical intramolecular charge transfer (ICT) compounds, are of tenused many are as such as light emitting diode design [11,12], ion sensor , labeling  due to their high fluor- escence quantum yields and strong fluore scence properties. Although there are many studies on pyrazoline derivatives focusing on their synthesis and/or several bioactivities, unfortunately, there are very limited number studies on the pH sensor application of pyrazoline de- rivatives . Indeed, pyrazolines have several advantageous over the other sensor candidates since they can be synthesized easily and have excellent fluore scence property. Therefore, new pyrazoline derivatives which subject to this investigation can provide very valuable informa- tion to there searcher working on the development on pH In this study, new “off-on-off” type fluore scence pH sensors which has pyrazoline structure were designed (Scheme 1). Pyrazolines studied here have the chemical structure of 4-(5-(3,4-dimethoxyphenyl)-3-(4- substitute dphenyl)-4,5-dihydro-1H-pyrazol-1-yl)benzene sulfonamide in which R was H (D1), F (D2), Cl (D3) and Br (D4). It was aimed to investigate the effect of pH on the optical properties of the pyrazolines D1–D4 considering them as new “off-on-off” type fluore scence pH sensors candidates. For this purpose, it was planned to take UV–Vis. Absorption and fluore scence measurements of the compounds D1–D4 and to calculate their photo-physical parameters. The information to be obtained by this study will be useful to the people who are working on the development “off-on-off” type fluore scence pH sensor on which very limited information is available. In addition, it will be verycon- tributory to the uses of pyrazolines as pH sensors since there are very limited studies related to uses of pyrazoline as pH sensor. Pyrazoline derivatives D1–D4, an “off–on–off” type of pHfluor- escent sensor, were freshly synthesized. Their optical behaviors were determined in water. D1 had high fluorescence in the blue-green region and the fluorescence intensity but when hydrogen was replaced by halogen, fluorescence intensity decreased. It was also examined the effect of pH on the fluorescent properties of compounds D1–D4. The fluorescent properties of D1–D4 exhibited important changes de- pending on pH value. These important changes that the compounds D1–D4 have “off-on-off” type of fluorescent pH sensor properties based on ICT. The obtained results indicated that the sepyrazoline derivatives would be able to act as an efficient “off-on-off” fluorescent pH sensor in biological, environmental and medicaletc. areas.
Keywords - Pyrazoline
Off-on-off fluorescent pH sensor.