Synthesis And Spectral Properties Of Some Novel Schiff Bases With Solvatochromism And Fluorescence Proton Switches

Schiff base compounds have elicited intense interest for their outstanding tautomers and the wide applications in photochromism, light storage, organic photoelectric functional materials and functional information materials. However, there are relatively few investigations on the application of Schif base as fluorescence probes and fluorescence molecular switches, because of their structure and properties. In this paper, taking use of the tautomers of the pyrazolone and salicylaldehydes derivatives, three Schiff bases compounds with different structures containing naphthalimide as fluorescent particle were prepared: N-dodecyl- 4-(1-phenyl-3-methyl-4-benzoyl-5-pyrazolone-methyl-imino-hydrazine)-1,8-naphtha-limide(S1), N-[2-(2-hydroxyethoxy)ethyl]-4-2-hydroxybenzaldehyde-hydrazone)- 1,8-naphthalimide(S2), N-[2-(2-hydroxyethoxy)-ethyl]-4-[2-hydroxy-4-(N,N-diethyl -aminosalicyl)-benzaldehyde-hydrazone]-1,8-naphthalimide(S3). Then, in order to explore the fluorescence dimers, compound S4 was prepared: 1,4-dimethoxy-p- benzaldehyde-di-(N-dodecyl-4-hydrazine-1,8-naphthal-imide)-hydrazone(S4).Then, the spectral properties were investigated detailedly.The spectrum properties of the three compounds (S1, S2, S3) were investigated detailedly through the UV-Vis absorption spectra and fluorescence spectra of the three compounds in different solvents. It shows that, the solutions of the Schiff base compounds behaved evident solvatochromism in solvents of different polarity owing to the characteristic tautomers of the pyrazolone compounds and salicylaldehyde schiff bases. The absorption spectra of the Schiff base solutions have a red shift and even behave color change with the increase of the solvents'polarities. The color of the solution changes from yellow in non-polar solvent toluene to red or purple in polar solvent DMF. The researches on the fluorescence spectra show that the fluorescence emission apices and fluorescence emission intensity arises different variety with the changes of the solvents'polarity. The relations between the solvents'polarity and the max fluorescence emission apices of the three compounds were reviewed, but these two factors don't match each other in evident linearity relation. The three compounds all manifest special solvent effects.The special solvent effects of the three compounds may be aroused by many factors, such as the intramolecular or intermolecular hydrogen bonding and the tautomers conversion induced by the solvents.The spectrum properties of the three compounds were investigated detailedly by the UV-Vis absorption spectra and fluorescence spectra of the three compounds in ethanol-water solutions with different pH. The three compounds behave acidichromism properties. They are yellow in acid solutions and amaranth in basic solutions. They can be applied as indicator in analytical chemistry, environmental monitoring. There is a strong fluorescence emission attaching the naphthalimide section of those compounds in acid solutions. But the fluorescence emission is weaker in basic solutions than that in acid solutions, sometimes the fluorescence emission even quenched. Those phenomena are likely to be aroused by the protonation and de-protonation of the schiff base structure in solutions with different pH, the formation and disintegration of the intramolecular or intermolecular hydrogen bonding and other sensitive factors. Those factors affect the intramolecular electron transfer of the schiff base. The photo-physics and photochemistry processes form fluorescent molecule switch controlling by proton. Those compounds can be used as fluorescence chemical sensors controlling by proton and metal ion.The spectrum property and aggregates of compound S4 was characterized by ultraviolet spectrometer, fluorescence spectrometry, DSC, X-ray diffraction and TEM. The result shows that the compound is a red fluorescence material, but it hasn't special aggregates.