Rhodamine B-thiourea Derivatives Synthesis Of Fluorescent Probes Identify The Role Of Metal Ions

The design and synthesis of selective chemosensors for detection of different target species is a hot subject in the field of supamolecular chemistry, chemical, biological and environmental assays in recent years. The most particular interests in this field are fluorescent chemosensor, because they could achieve a quick sensing of a specific analyte by a simple fluorescent enhancement (turn-on) or quenching (turn-off) response. Rhodamine compounds are one type of the xanthene dye. Rhodamine derivatives are excellent fluorescent chemosensors due to their excellent photophysical properities such as long absorption and emission wavelength, large molar extinction coefficient, high fluorescence quantum yields and high light stability. The mechanism involves the well-known transformation of spirolactam form (fluorescence "off") to a ring-opened amide form (fluorescence "on") in the presence of metal ion or proton.In this dissertation, starting from Rhadamine B, five Rhadamine B-thiourea derivatives were synthesized and fully characterized. Firstly, RhB-B was obtained in base solution. RhB-HD was synthesized through condensation reaction between RhB-B and hydrazine hydrate, and then reacted with a series of phenyl isotiocyanate to form five Rhadamine B-thiourea derivatives: RhB-PhTh, RhB-pNPhTh, RhB-pMOPhTh, RhB-2MO4NPhTh and RhB-4MO2NPhTh. The structures of all Rhadamine B-thiourea derivatives were characterized by the Fourier Transform Infrared (FT-IR) spectra, Mass spectra (MS) and proton nuclear magnetic resonance (1H NMR) in detail.The sensoring properties of Rhodamine B-thiourea derivatives for metal ions were then studied by fluorescence and UV absorption spectroscopy. The results show that all Rhadamine B-thiourea derivatives can selectively sensoring Cu2+. Then the opitomal conditions of the proposed method were studied. Furthermore, under the same conditions, the experiment was conducted to compare the different sensing properties of the Rhodamine B-thiourea derivatives for Cu2+. The results indicated that the fluorescence intensity at 581 nm of RhB-2MO4NPhTh for Cu2+ mixed with common metal ions exhibited no obvious change. So RhB-2MO4NPhTh displays more sensitive than other Rhodamine B-thiourea derivatives in Tris-buffered acetonitrile aqueous solutions. The results indicated that push electron compounds improved the effect of Cu2+ sensing. So we can use push electron compounds to make advanced Cu2+ sensor.