Pyrimidine-based BF₂ Complexes:Synthesis And Photophysical Properties

Organic fluorine-boron complexes,with BODIPYs(boron diprromethene and its derivatives)as the example,are a family of best-known fluorescent dyes with some excellent properties.Their high absorption coefficients and quantum yields,and tunable emission from visible light to near infrared allow BODIPYs to be applied in the field of fluorescence sensing and imaging,and light harvest.Unfortunately,most of BODIPYs diplay rather low Stokes shift of typically 7-15 nm,which would result in self-absorption of their emitted photons.Moreover,BODIPYs often show nonfluorescence in the solid-state due to aggregation-induced fluorescence quenching.Therefore,great efforts have been paid to the design and synthesis of BODIPYs with large Stokes shift and intense fluorescence in the solid state in recent years.To address this need,in this paper,we present the synthesis and photophysical properties of a seires of pyrimidine based boron difluoride complexes with large Stokes shift and intense fluorescence in the solid state.The relationship between the structure and the optical properties of these new BODIPYs are studied.This research will result in the discovery of new design strategies for the development of new BODIPYs.1.A new family of BODIPY analogues(1-8)with excellent fluorescent properties both in solution and solid-state were synthsized.These new luminophores exhibited intense and tunable fluorescence with quantum yields ranging from 0.13 to 0.90,and moderate Stokes shift ranging from 500 to 1200 cm-1 in solution.In solid-state,1-8 showed asymmetrization-induced solid-state emission with moderate quantum yields ranging from 0.18 to 0.36.In addition,compounds 4,5 and 7 exhibit a reversible chromic response to grinding.The short synthesis routes,facile structure modifications,good optical properties in solution/solid-state,and piezochromic behaviour of these novel boron dyes(1-8)will make them potential candidates for smart materials.2.A new family of pyrimidine-based BF2 complexes(9-12)have been developed.These new luminophores were demonstrated to possess AIE,tunable,substituent-dependent emission profiles,large Stokes shift and high quantum yield in the solid-state.In addition to their pronounced AIE behaviour,compound 12 also exhibits reversible chromic response to grinding,and a distinct red-shift of emission is observed.The high solid-state luminescence and grinding-stimuli response properties of these compounds make them potential candidates for smart materials.3.The diboron compounds with a greater extent of ?-conjugation than monoboron dyes,giving great potential to use in electroluminescent(EL)devices.The diboron-containing fluorophores(13-15)with infrared emission were designed and synthesized.The quantum yield of compounds 13-15 were 0.12,0.35,0.18 in solid-state,respectively.Due to the increase in the number of phenyl groups,the rotation of the phenyl ring is hindered due to the increased steric hindrance,which make these compounds show moderate fluorescence quantum yield in solution.The high solid-state luminescence and far-red emission properties of these compounds make them hold great potential for bioimaging and electroluminescence applications.