| Organic fluorescent materials have been widely used in organic light-emitting devices(OLEDs),cosmetics,anti-counterfeiting and modern biology due to their good fluorescence properties.Coumarin derivatives are important small molecule fluorophores because of their excellent photophysical properties such as large Stokes shift and high fluorescence quantum yield.Because of their large conjugated system and strong electron transfer ability,the introduction of functional groups will affect the function and fluorescence properties of coumarin derivatives.Based on the steric hindrance and intramolecular charge transfer effect of different substituents,a strong electron-donating group diethylamino and several electron-withdrawing groups with different abilities were introduced to the 7-and 3-positions of the coumarin skeleton,respectively,to synthesize a series of coumarin derivatives with different luminescence properties,and systematically analyzed the decisive role of structure in the luminescence properties.Meanwhile,the prepared fluorescent powder is applied to a warm white light LED device.The first part introduces the development and application of coumarin.In recent years,based on the excellent photophysical properties of coumarin,a variety of coumarin derivatives have been developed,which have been widely used in fluorescent probes,organic light-emitting diodes and photosensitive dyes in solar cells.In the second part,coumarin derivatives BM1 and BM2 were obtained by introducing diethylamino group at the 7-position and malononitrile and phenylmalononitrile groups at the 3-position of coumarin,respectively.These two compounds have obvious solvation effects.From the low polarity solvent n-hexane to the high polarity solvent dimethyl sulfoxide,the fluorescence emission peaks of compounds BM1 and BM2 are red-shifted by 67 nm and 124 nm,respectively.Compound BM2 showed strong fluorescence emission in pure tetrahydrofuran solvent,and its molecules would aggregate and cause fluorescence quenching when the poor solvent water was added.Based on this,BM2 was applied to the determination of trace water in tetrahydrofuran with a detection limit of 0.027%.The fluorescence properties in the solid state show that BM2 with extended conjugated structure has a higher fluorescence quantum yield than BM1.Density functional theory(DFT)calculations and single crystal structure analysis further clarify the influence of structure on the properties.In the third part,coumarin derivatives with D-π-A structure were synthesized by introducing three different electron-withdrawing groups with benzene ring at the 3-position of coumarin after fixing the substituent at the 7-position of coumarin as the strong electron-donating group diethylamino.They all have significant solvation effects in different solvents.The fluorescence properties in the solid state show that the emission color of the compound shifts from cyan of BM3 to yellow of BM5,and the emission of substituent-controlled molecules is realized with the gradual decrease of the fluorescence quantum yield in the solid state.Density functional theory(DFT)calculations and single crystal structures systematically analyze how the substituents modulate the luminescent properties of the molecules.The fluorescence quantum yield of BM3 is 98.2%in solid state and 77.1%in solution.And a very effective idea is provided for constructing efficient luminescent material in a double state.In the fourth part,deep red compound BM2 and cyan compound BM3 were applied to warm white LEDs,and the maximum brightness of the devices reached52090 cd/m~2 at the working voltage of 3.2 V,and strong white light was observed by naked eyes.The CIE color coordinate is(0.4121,0.4454),the lower correlated color temperature is 3747 K,and the suitable color rendering index is 78. |
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