Synthesis And Application Of Squaraine-Based Organic Solid Red Fluorescent Materials

Organic solid red luminescent dyes are one of the indispensable three primary color（red,green,blue）materials for full color display.And red to near-infrared emitting materials are highly desirable for biomedicine applications due to their particular advantages of low optical absorption,little autofluorescence in biological media and deep tissue penetration for efficient emission detection.However,there have been relatively few reports of highly efficient organic solid red fluorescent materials,and solid red emission materials based on squaraine dyes（SQs）have not been reported.Based on the above necessity of preparing organic solid red luminescent materials,high-efficiency 1,2-squaraine dyes（1,2-SQs）and 1,3-squaraine dyes（1,3-SQs）were prepared by simple synthesis methods.The fluorescence quantum yield was up to 92.93%.The optical properties and molecular structure were determined by means of visible-ultraviolet absorption spectra,fluorescence spectra,¹H NMR,¹³C NMR,MS and XRD.The experimental results were as follows:（1）In the second chapter,a new family of asymmetrical 1,2-squaraine dyes（1,2-SQs）were designed and synthesized in high yields,named SQ1-5.The results analysis presented that these 1,2-SQs showed weak fluorescence in solution but strong red fluorescence in crystal state,suggesting their aggregation-induced emission enhancement（AIEE）properties.Single crystals X-ray diffraction revealed that the intense fluorescence in the crystal state could be attributed to the effects of side chain group（alkyl chain or benzyl group）substituents in the molecules,which efficiently prevented the tightly intermolecular contact and reducedπ-πinteractions.In view of the above excellent optical properties,the biocompatibility and cell imaging applications of SQ4 were further investigated.The results demonstrated that SMMC-7721 cell could be clearly imaged by SQ4,which inferred SQ4 had excellent biocompatibility and potential value for bioimaging.（2）In the third chapter,two simple asymmetrical 1,3-squaraine dyes（1,3-SQs）were easily designed and prepared in high yields,named SQY1 and SQR2 which exhibited diverse emission properties:large Stokes shift,super intense crystal red emission,dual-state emission（DSE）and solvatochromism.Among them,SQR2showed strong red crystal emission at 633 nm with a quantum yield of 92.93%,which was a recorded high value for squaric acid-based dyes ever reported.X-ray Single crystals diffraction revealed that their large difference in crystal emission owing to their distinct stacking structures:J-aggregation for SQY1 and a staggered structure（X-aggregation）for SQR2.The stacking mode of molecules allowed them to emit strong crystal fluorescence and large red shift relative to in various solvents.And we also explored the application of SQR2 in cell imaging.Our research can further provide a profound understand the luminescence mechanism of DSE and solvatochromism properties.