The Effect Of Steric Configuration On Luminescence Properties Of Coumarin Fluorescent Materials

Coumarin is a common organic fluorescent dye.Its derivatives have a wide range of applications in the fields of LEDs,laser dyes,drug synthesis,and biosensing because of its large conjugated system,rigid planar structure,and easy to modify molecular structure.Most coumarin derivatives have excellent luminescence properties in solution,but the ?-? interaction due to molecular packing in the aggregated state causes their fluorescence intensity to decrease or even quench.Scientists have found that molecules with larger spatial effects can effectively reduce the energy loss caused by the intermolecular ?-? stacking,and show strong fluorescence in the solid state.However,the free rotation of the single bond in the molecule causes the non-radiative transition of the excited molecule,resulting in a weak fluorescence intensity in the solution.Later,the research group of Tang Benzhong found that the twisting of the spatial configuration of molecules can not only effectively reduce the ?-? interaction between molecules,but also inhibit the free rotation of single bonds in the molecules,so that the molecules have strong fluorescence emission in the solid-liquid state.In this paper,a series of organic fluorescent molecules with different luminescent properties were obtained by introducing different substituents at different sites of coumarin.The effect of different substituents on the regulation of the spatial distortion of molecules and their fluorescent behavior was studied.1.Taking 3-p-trifluoromethylphenylthiophene coumarin as the main body and introducing substituents with different electron-donating abilities at the7-position.The coumarin derivatives with 7-positions of hydroxy substitution(TCM1),hexoxy substitution(TCM2)and acetoxy substitution(TCM3)were synthesized.All three compounds show strong fluorescence emission and obvious negative solvation in organic solvents.In the system with low water content,the compound exists in the form of a single molecule,and its fluorescence intensity remains basically stable.In the system with high water content,the fluorescence quenching due to molecular aggregation has a significant effect of aggregation fluorescence quenching(ACQ).TCM1,TCM2 and TCM3 all show yellow fluorescence in the solid state.The fluorescenceintensity of TCM3 is much higher than that of TCM1 and TCM2,and the fluorescence quantum yield is 23.47%.Compared with TCM1 and TCM2,TCM3 has a longer fluorescence lifetime,with a value of 7.99 ns.2.Using 7-diethylaminocoumarin as the main body,the coumarin derivatives with p-trifluoromethylphenylthiophene(TCM4)and p-formylphenylthiophene(TCM5)at the 3-position were synthesized,where TCM4 has obvious negative solvation properties.TCM4 exhibits high and stable fluorescence emission in systems with low water content,and fluorescence quenching occurs in systems with high water content;The fluorescence intensity of TCM5 shows a slowly decreasing trend with increasing water content and ACQ effect.In the solid state,the fluorescence colors of TCM4 and TCM5 are orange and red,respectively.The fluorescence intensity of TCM4 is higher than that of TCM5,and the fluorescence quantum yields are 15.39% and 13.61%,respectively.The transient fluorescence spectrum show that the fluorescence lifetime of TCM4 and TCM5 are 3.71 ns and 3.23 ns,respectively.