Fluorescent Probes And Stimuli-responsive Materials Of Azine Derivatives Based On Aggregation-Induced Emission

Aggregation-induced emission (AIE) is a unique phenomenon thatAIE-active compounds exhibit weaker fluorescence in solution but strongerfluorescence in the aggregated state. Unlike traditional fluorescent dyes,AIE-active compounds effectively avoid the self-quenching of fluorescenceinduced by aggregation. Salicylaldehyde azine derivatives, facilely prepared bythe condensation between the corresponding salicylaldehydes and hydrazine,displayed such unique AIE property. Induced by the intrameocular hydrogenbond between the Schiff base’s nitrogen and ortho-hydroxyl group, the rigidsix-membered ring in salicylaldehyde azines allowed free rotation of themolecules around N-N single bond, thus leading to their fascinatingaggregation-induced emission property. Therefore, the aforesaid uniqueemission behavior endowed salicylaldehyde azine derivatives with greatpotential in developing new fluorescent probes and solid fluorescent materials.Given the convenience of preparation and the unique emission behavior,this dissertation was aimed at developing new fluorescent probes and solidfluorescent materials of azines based on the aggregation-induced emission.Firstly, an analytical approach based on AIE mechanism to detectpyrophosphate (PPi) was established with5-chlorosalicylaldehyde azine as theturn-on fluorescent probe. With the aid of selective binding between copper(II)cation and5-chlorosalicylaldehyde azine, a complex system based on AIE wasconstructed and applied in the detection of PPi with the detection limit at0.064μM. Secondly, novel benzophenone azine, exhibiting AIE and thermochromismproperties, was designed and generated by the incorporation of free-rotatingphenyl ring with the conformational flexibility into the scaffold ofsalicylaldehyde azine. Conformational changes of phenyl ring induced bythermal stimuli accounted for the thermochromism. Upon thermal annealingtreatment, the larger conformational rotary of phenyl ring promoted strongerintermolecular interaction and tighter packing mode, and consequently theemission was shifted to longer wavelength. Upon melting treatment, the aforesaid stronger intermolecular interaction was destroyed to release themolecules in the loose packing mode in the crystal structure, and consequentlythe emission was shifted back to shorter wavelength. Thirdly, novel AIEmaterial octanoxyl-substituted benzophenone azine, displaying reversiblethermochromism and vapochromism properties, was designed and produced bythe combination of long alkyl chains with the scaffold of benzophenone azine.Accompanied with the conformational change of the flexible alkyl chain, threedifferent types of packing model, including monomer-like aggregate packingmode, J-aggregate packing mode and the special herringbone packing mode thatcomposed by dimer units, were observed in the crystal structure with theemission red-shifted from534nm to543nm further to558nm. Upon thethermal stimulation, the metastable packing modes of monomer-like aggregateand J-aggregate in the crystal both can be converted to the thermal stableherringbone packing mode, and consequently the emission was red-shifted.Upon exposure to organic vapor, π-π stacking interaction in the dimer units wasdiminished due to the change of alkyl’s conformation and local dipoleinteraction, and thus the emission was blue-shifted.