Synthesis And Study On Light-emitting Properties Of 5h-indeno[1,2-b]pyridin-5-one Derivatives

In recent years,OLED display technology has developed rapidly,and it is likely to replace LCD as a new generation of display.The OLED display is a self-luminous type display device.It is very necessary to study the luminescent material for it plays an important role in the OLED display industry.At present,most of the luminescent materials used in commercial OLED are phosphorescent materials,which are mainly due to the high luminous efficiency and high emission and thermal stability of such materials.But such materials generally contain precious metals,thus causing they are very expensive,and raising OLED production costs.Thermally activated delayed fluorescence（TADF）materials are considered to be the most promising luminescent materials in the third generation displays.Due to the extremely small singlet-triplet energy difference(?E_ST),triplet excitons can be upconverted to singlet states to emit delayed fluorescence and achieve 100%exciton utilization.The challenge of developing TADF materials is to explore electron acceptor groups with excellent performance.This paper aims to design novel acceptor groups and prepare neoteric TADF materials to study their luminescent properties.A large number of TADF molecules that contain carbonyl units as acceptor have been discussed in the literature.In this paper,a novel cyclic ketone,i.e.,5H-indeno[1,2-b]pyridin-5-one（IP）,was synthesized as an electron acceptor unit.A series of new luminescent molecules were designed and synthesized by changing electron-donating group and tuning the position between the electron acceptor group and the electron donating group.In order to study their electroluminescent properties,they are prepared OLED devices.The specific research contents are as follows:Taking IP as the electron acceptor,firstly,carbazole（Cz）was used as the electron donor.By adjusting the substitution position of Cz on IP,a series of isomers of D-π-A structure were designed and synthesized,namely IP-6-PhCz,IP-7-PhCz,IP-8-PhCz and IP-9-PhCz.It was found that the substitution positions of Cz on the IP ring will cause large change in the molecular conformation and their luminescent properties are significantly different.Due to steric repulsion between the Cz group and the carbonyl or pyridine on IP,twist angles of IP-6-PhCz and IP-9-PhCz are as high as 45.3°and 51.8°,respectively.The large twisted configuration of IP-6-PhCz and IP-9-PhCz result in long-lived fluorescence withμs scale.Temperature-dependent transient PL decays were measured to confirm whether TADF or not.While IP-7-PhCz and IP-8-PhCz are just ordinary fluorescent molecules without long-lived fluorescence.The planar structure of carbazole group may be the main reason for the low fluorescence quantum yield of the luminescent molecule.To this end,a new luminescent material with similar structure was designed with triphenylamine as the electron donor,namely IP-6-TPA,IP-7-TPA,IP-8-TPA,IP-9-TPA.Theoretical calculations show that the HOMO distribution of the new materials are more dispersed and extensive,which results in the fluorescence quantum yield of these molecules significantly increase(from 4%-35%to 23%-70%.The6-and 9-position isomers also have large twist angles（46.4°and 49.6°）and possess small?E_ST at the same time,which lead to TADF property with lifetime inμs scale.The performance of devices confirmed that the materials which using triphenylamine as the donor are generally better than the carbazole ones.Among them,IP-6-TPA achieved the best performance in the device as the luminescent guest material,and the maximum external quantum efficiency is 9.0%.