Design,Synthesis And Luminescence Properties Of Novel Acridine-imidazole Small Organic Molecules

Organic luminescent materials have gradually attracted the attention of scientists since the 1980 s.As more and more luminescent molecules leap into people’s field of vision,Luminous materials with excellent performance are widely used in scientific research and people’s livelihood in display technology,medical imaging,anti-counterfeiting,etc.Among them,imidazole is a molecular building group of common blue light materials.In addition to being used as a high-efficiency blue light material,its intrinsic bipolar electronic structure also plays a very good role in balancing charge transport in the field of organic electroluminescence.In this thesis,a series of new acridine imidazole positional isomers were designed and developed,and their luminescent properties were systematically studied.The specific work is as follows:In the first part,a pair of isomers(1a and 1c)were synthesized by fusing acridine derivative to C4-C5 of imidazole.Their single crystal were successfully obtained by solvent diffusion method.We have studied the properties of UV,fluorescence,electrochemistry,solvation and acidchromism,and found that the pair of isomers showed significant differences in luminescence properties.According to the analysis of the single crystal structure,there is a strong CH/π interaction between the methyl group and the adjacent benzene ring in 1c,leading to the bent polyarylene imidazole plane.This results in a decrease in the overall conjugation of the molecule and avoids the formation of a strong π-π packing.Additionally,the different linking sites of methyl on imidazole may induce the difference of their charge transfer excited state,which should be the main reason for the different luminescent properties of this pair of isomers.In order to further study the relationship between structure and luminescentproperties of this kind of molecules,in the second part,we introducds some push-pull electron groups in the para position of the benzene ring at the 2-position of imidazole,and successfully synthesized six acridinium-imidazole isomers.We have also studied the properties of UV,fluorescence,electrochemistry,solvation and acidchromism.It is found that the electron-donating groups induce fluorescence emission peak red-shifted,while the electron-withdrawing groups make fluorescence emission peak blue-shifted.Each pair of isomers also showed the similar results on their photophysical and electrochemistry properties as those of 1a and 1c.In comparison with a-isomers,all c-isomers exhibited higher quantum efficiency except for 3a/3c.According to the single crystal structure analysis,the intramolecular interaction steric hindrance in the induce the polyaryl imidazole plane bent in c-isomer,,resulting in a decrease in conjugate degree of the whole molecule,and avoiding strong π-π interactions.Considering there is not obvious planarity difference in crystal of 3a and 3c,the lower quantum efficiency of 3c should be from its stronger CT characteristic.