Research On D-π-A Small Molecular NIR Dyes

Our project focused on one special kind of molecule in chemical structure—small fluorescent molecule.Its particularity lies in the fact that although the conjugated structure is common in the field of organic synthesis,it is quite challenging to construct stable and outstanding fluorescent molecules.Since the establishment of the discipline of chemistry,whether organic chemists or physical chemists,they have been making continuous effort to expand the fluorescent molecular bank.Since the fluorescence has been used in all aspects of human daily life,the nature of fluorescence is closely related to the molecular structure,such as photoluminescence,thermoluminescence,mechanoluminescence and so on.In this project,we focused on exploring small fluorescent molecules,which are excited by ultraviolet-visible light and able to emit near-infrared light.The near-infrared region（780～1100nm）is the ideal range for the excitation wavelength of fluorescent molecules,because in practical applications,no additional organic solvents are required,and the fluorescence is obvious.The result can be obtained within 20 seconds under the measurement of fluorescence excitationemission spectrum;of course,it may take a little longer for the measurement of cells and tissues.The detection in this spectral region wouldn’t damage the properties of the sample,nor would it damage the normal growth of tissues or cells.Therefore,near-infrared fluorescent small molecules have relatively good safety and strong application value.First,compounds based on 4H-1-benzopyran core were rationally designed and synthesized;and,these compounds had wide Stokes shifts and are able to emit bright and penetrating red fluorescence,but they failed to overcome aggregation quenching.Therefore,on the basis of the coumarin,we synthesized compounds based on 1,1-Dimethylnaphthalene-2（1H）-one core,which can effectively overcome aggregation quenching,but we had to sacrifice part of the excitation-emission gap and these compounds failed to reach the near-infrared region,so,the main compounds are able to emit bright green fluorescence.It was worth mentioning that the two series of compounds designed and synthesized in this project had been confirmed to be non-toxic fluorescent small molecules in biological tests,and due to their small molecular weight,they could smoothly pass through the cell membrane,penetrate deep into cells and tissues.Herein,the advantageous compounds mentioned in this project are all fluorescent molecules with strong applicability.Consequently,the dominant compounds like M-3,NC-4-Br,NC-4-Ph in this project had excellent stability and fluorescence properties,with strong probe potential,which would pave the way for the subsequent synthesis of specific fluorescent probes.