Synthesis And Fluorescent Properties Of Benzimidazolyl Coumarin Derivatives

Coumarins constitute the largest class of laser dyes in the‘blue-green'region.Due to their inherent photochemical characteristics and stability,coumarin derivatives had been extensively investigated for charge-transfer agents,emissive dopants and organic light-emitting diodes?OLEDs?application.In this thesis,derivatives modified with benzimidazole and phenanthro[9,10-d]imidazole ring at the 3-and 4-positions of coumarin were designed and synthesized,the relationship of their photoluminescence properties and structure was investigated.The paper mainly composed of three parts.In the first part,the synthesis and application of coumarin fluorescent compounds and benzimidazoles,as well as the luminescence principle and fluorescence parameters of fluorescent compounds were introduced.Then,we illustrate the research content and the basis of the topic.In the second part,the synthesis and fluorescent properties of benzimidazolyl coumarins and phenylimidazolyl coumarins were studied.Four benzimidazolyl coumarin fluorescent compounds and four phenylimidazolyl coumarin fluorescent compounds were synthesized by the reaction of 3-formlycoumarin and 4-formlycoumarin respectively with 3,4-diaminotoluene,N-phenyl-o-phenylenediamine,benzil and aniline.The structures of synthesized compounds were characterized by ¹H NMR,¹³C NMR and IR.The evaluation of the fluorescent properties of these coumarins show good fluorescent properties,4-substituted coumarins have the obvious solvatochromic effect.The frontier orbital energy levels and energy gaps were calculated by density functional theory?DFT??B3LYP/6-31G?d,p??of quantum chemistry,the results shown that the energy gaps were lower resulting in UV-vis absorption spectra gaps redshift.The high fluorescence quantum yields and lifetimes,desirable frontier orbital energy levels of products indicated that the combination of coumarin and benzimidazole or phenylimidazole is an efficient way to enhance the application potential of products in optical materials.The crystal structures of 7-?diethylamino?-3-?1-phenyl-1H-benzimidazol-2-yl?coumarin?4b?and 7-?diethylamino?-3-?4,5-diphenyl-1H-imidazol-2-yl?coumarin?5a?were analyzed by X-ray single crystal.In the third part,the synthesis and fluorescence properties of phenanthro[9,10-d]imidazolyl coumarin derivatives were studied.7-?Diethylamino?-3-?1-phenyl-1H-phenanthro[9,10-d]imidazol-2-yl?coumarin?9?and its isomer 7-?diethylamino?-4-?1-phenyl-1H-phenanthro[9,10-d]imidazol-2-yl?coumarin?10?were synthesized by the reaction of3-formlycoumarin and 4-formlycoumarin respectively with 9,10-phenanthraquinone and aniline.The structures of synthesized compounds were characterized by ¹H NMR,¹³C NMR and IR.The compounds 9 and 10 possess similar structures but have different linking positions between the phenanthro[9,10-d]imidazole and coumarin moieties,the fluorescent properties of them were tested and analyzed comparatively.The maximum UV-vis absorption wavelengths of the compounds 9 and 10 in CH₂Cl₂ were at 409 nm and 402 nm,the maximum emission wavelengths were at 490 nm and 509 nm,and the Stokes shifts were 81 and 107 nm,respectively.The absolute fluorescence quantum yields respectively were 87.97%and 57.91%,fluorescence lifetimes were 2.65 ns and 5.69 ns in CH₂Cl₂ solution.The maximum emission wavelength in solid states were at 523 nm and 476 nm,respectively,the quantum yields in solid states were 14.10%,0.82%,and lifetimes were 3.36 ns,0.49 ns.The results indicated that the compound 9 has stronger intramolecular charge transfer character and larger conjugation than the isomer 10.The influence of phenanthro[9,10-d]imidazole linked at the 3-and 4-positions of coumarin on the frontier orbital energy levels of the molecules were theoretically predicted by the quantum chemical calculations,the results shown that the frontier orbital of the molecules increased with the enhancement of the electron cloud density of the conjugated system.The phenanthro[9,10-d]imidazolyl coumarin molecules were calculated that the energy gap of compound 10 was larger than that of the isomer 9.The energy gaps were lower resulting in UV-vis absorption wavelengths redshift,the results indicated that the frontier orbital energy was closely related to the UV-vis absorption spectrum property.From the analysis of the optimal geometry,it's found that the wide energy gap can be obtained by increasing the twist angle of the molecular structure.