Coumarin-based Probes For Metal Ions: Molecular Design, Synthesis And Properties

A series of probes with various receptors attached to coumarin fluorophores were designed for the detection of metal ions. Their sensitivity to solvent polarity and recognition ability to metal ions were studied through the UV and FL spectra.Twelve of single- and double-armed probes were designed by introducing various receptors containing N, O and S atoms to the comarins. The fluorescent probe with single-armed receptor, 3-N-(2-hydroxyethyl)carboxamido-7-(diethylamino) coumarin (E1) shows remarkably sensitivity and selectivity response to Fe3+, which was turned out as an ICT mechanism. In others with double-armed receptors, the probes 4-(N,N-bisacetoxyethylaminomethyl)-7-methoxycoumarin. (B3) and 4-[(N,N- bis(diethylaminodithiocarboxyethyl aminomethyl)-7-methoxycoumarin (B4) with pronounced fluorescence enhancement response to special heavy and transition metal ions were proposed as PET mechanism; for those with double-armed receptors following ICT mechanism, their performances are influenced by not only the structure of the receptors but also the attaching position of it.Thirteen fluorescent probes with twin coumarin fluorophores were designed. When 6,10-dimethyl-2,6,10,14-tetraazapentadecane was introduced as spacer and receptor. The probe 2,6,10,14-tetramethyl-1,15-bis(7-methoxy-4-coumarinyl)-2,6,10, 14-tetraazapentadecane (G4) based on PET mechanism was found to enhance the fluorescence intensity to 100 times, which can be used as fluorescent switches for protons. This probe can also recognize Hg²⁺ and Fe³⁺ sensitively in aqueous solution. The colorimetric sensors used to the detection of Fe³⁺ are very scarce. In this thesis, sensors N,N-bis(7-diethylamino-3-coumarinformyl)-m-phenylenebis(methylamine) (H3), N,N-bis(7-diethylamino-3-coumarinformyl)hexanediamine (H4) were found to show excellent selectivity towards Fe³⁺. Two sensors 1,9-bis(4-methoxy-7- coumarinoxy)-3,7-dithianonane (I1), 1,8-bis(4-methoxy-7-coumarinoxy)-3,6- dithia- octane (I2) for recognition of Hg²⁺ were also obtained by introducing 1,3-bis(methylthio)propandiyl and 1,2-bis(methylthio)ethandiyl respectively as the spacer.Nine probes based on the C=N isomerization were also synthesized and it was found that two probes 3-(2-hydroxyphenyliminomethyl)-7-diethylaminocoumarin (J1), 3-[(4-bis(2-hydroxyethyl)aminophenyliminomethyl]-7-diethylaminocoumarin (J2) show fluorescence enhancement to Cu²⁺ significantly, which can be used for trace measurement of Cu²⁺ in the enviroment. Another probe 7-diethylamino -3-cumarinaldehyde thiosemicarbazone (J9) was found as colorimetric sensor to Fe³⁺.