Synthesis And Photophysical Properties Of Carbazole/phenothiazine Modified Fluoroboron Dyes

Boron-dipyrrolidene(BODIPY or BDP)fluorescent dyes have a wide range of applications in the fields of optoelectronic materials and biomedicine due to their unique photophysical properties,such as higher fluorescence quantum yields,larger molar extinction coefficients,better photostability,and a wide variety of easy modifications.Therefore,it has become an interesting object of research in recent years.Although BDP dyes have strong fluorescence emission in solution,due to the planarity and symmetry of the molecules,the Stokes shifts are usually small.At the same time,the strong ?-? interaction between molecules enhances tight packing in the solid state,and thus strong self-absorption,causing fluorescence quenching.Therefore,changing the symmetry of the nucleus of BDP to suppress the close packing of molecules with complete overlap and to increase the Stokes shift of the system by the difference of charge distribution between the ground state and excited state will realize the solid-state luminescence of BDP molecules in the longer wavelength region.The group has earlier synthesized aza-pyridine isoindolinones as fluoroboron derivatives using 2-aminopyridine and 1-oxo-3-iminoisoindoline condensation,whose asymmetric structure inhibits the solid-state tight packing and thus has effective solid-state luminescence.In this thesis,the electron-rich groups carbazole and phenothiazine were introduced into the periphery of isoindolinones by a simple and efficient synthesis method to construct fluoroboron molecules with D-A structure.Carbazole and phenothiazine can increase the spatial site resistance and change the degree of conjugation of the system,resulting in enhanced intramolecular charge transfer ability,prompting spectral red-shift and improving solid-state luminescence efficiency.The main results are as follows:1.The rigid planar structure of the carbazole group is chemically stable due to its strong electron giving ability and good hole transport ability,and it can inhibit the aggregation of material solids,which will enhance the ICT effect of the system and increase the Stokes shift,and redshift the spectrum while achieving the solid state emission of the compound.The design idea of the first part of this thesis is to introduce two carbazole groups into 4,5-dichlorophthalonitrile,followed by oxidative condensation with N,N-diethylhydroxylamine,and then with aminopyridine and its derivatives to obtain intermediate compounds 3a,3b,3c and 5 with significant solid-state fluorescence,and finally with boron trifluoride ether to obtain a series of new asymmetric fluoroboron dyes modified with carbazole 4a,4b,4c and 6.The spectral properties of these compounds were tested and analyzed,and the absorption and emission wavelengths of these compounds were significantly red-shifted in polar solvents compared with those of the molecules before the introduction of carbazole,indicating that the introduction of carbazole increased the intramolecular charge transfer capacity and the Stokes shift,which led to the red-shift of the spectra.Meanwhile,fluorescence tests on the solids revealed that the emission wavelengths could reach 600 nm and above,with the longest wavelength being 678 nm,and the absolute fluorescence quantum yield of the solids could reach 0.30.It could be 0.5 s at low temperature(77 K),with typical phosphorescence.2.Phenothiazine,with its own electron-rich S and N,has a unique non-planar butterfly-like conjugated structure,which can effectively inhibit molecular aggregation,and when the molecule changes to the oxidized state,the phenothiazine ring will change to a relatively planar state,which is conducive to intramolecular charge transfer without causing solid fluorescence burst due to the strong ICT effect.Therefore,the phenothiazine oxidation group was introduced into the asymmetric nucleus.The compounds 11 a,11b and 11 c with solid-state fluorescence were obtained by the above synthesis method,and their molecular orbital energy level diagrams showed that the planarity was enhanced,the energy level difference was reduced,and the Stokes shift was increased compared with the BDP without the introduction of large-site resistance substituents,so that the solid-state emission and the accompanying spectral red shift were achieved.