Design, Synthesis And Recognition Properties Of Fluorescent Sensors For Ions Based On Coumarin

Detecting the level of transition metal ions and anions is of great interest to many scientists, including chemists, biologists, clinical biochemists and environmentalists. The advantages of fluorescenct sensors include conveniece, high sensitivity and selectivity, observation in situ, etc. The coumarin dyes have excellent photophysics and photochemistry properties such as high stability against light, high fluorescence quantum yields and big Stokes shift, etc. Therefore, fluorescent sensors based on coumarin have drawn much attention in recent years.The fluorescent sensors CHgl-3 for Hg2+ based on coumarin have been designed and synthesized via Hg2+-induced desulfurization reaction. In Tris-HCl neutral buffer, CHgl exhibits Hg2+-only sensitive among metal ions such as alkali (K+, Na+), alkaline earth (Ca2+, Mg2+), and transition metal ions (Cd2+, Ag+, Fe3+, Pb2+, Cr3+, Co2+, Ni2+, Cu2+, Zn2+). Upon the addition of Hg2+, there are a 12.5-fold intensity enhancement in fluorescence, a 20 nm red-shift in emission maximum and an obvious fluorescence change from almost colorless to bluish green. CHg2-3 have poorer recognition effects for Hg2+ than CHg1.p-OMe (electron-donating group) and p-NO2(electron-withdrawing group) on the aniline ring in CHg2-3 vary the electron cloud density around the molecular and ICT, which have interference on desulfuration reaction and the recognition effects.A boronic acid-linked fluorescent sensor CCul for Cu2+ based on coumarin has been designed and synthesized. In Tris-HCl neutral buffer, CCul exhibits Cu2+-only sensitive among metal ions. Upon the addition of Cu2+, there are a 5.7-fold intensity enhancement in fluorescence and a 9 nm blue-shift in emission maximum. Other metal ions and anions (C1O4-, CO32-, SO42-, F-, Cl-, Br-, I-, H2PO4-, AcO-, SCN-) have no obvious interference for CCul to detect Cu2+. The binding stoichiometry is 1:2 between CCul and Cu2+, and corresponding binding constant is 3.996×109 M-2. The coordination of CCul with Cu2+ is an irreversible process.A ratiometric and colorimetric sensor CCol based on intramolecular charge transfer (ICT) has been designed and synthesized. In Tris-HCl neutral buffer, CCol exhibits Co2+-only color response among metal ions. Upon the addition of Co2+, there are a 44 nm red-shift in absorption maximum and an obvious color change from yellow-green to orange-red. CCol displays fluorescence quenching response toward Co+. The binding stoichiometry is 2:1 between CCo1 and Co2+, and corresponding binding constant is (5.28±0.56)×l09 M-2. The coordination of CCol with Co2+ is an irreversible process.The fluorescent sensors CCNl-2 for CN- based on nucleophilic additional reaction have been designed and synthesized. In DMF, Upon the addition of CN-, there are a 95 nm red-shift for CCN1 and 89 nm for CCN2 in absorption maximum and an obvious color change from yellow-green to colorless. CCNl-2 display CN--only color change and fluorescence quenching response among the anions such as F-, Cl-, Br-, I-, HSO4-, H2PO4-, AcO-, CN-. Other anions have no interference for CCNl-2 to detect CN-.