Design,synthesis And Performance Study Of Blue Light Materials Containing Phenanthrimidazole Skeleton

In the 21st century,display technology is developing rapidly.The development prospects of OLED,which are the core of display technology,are unlimited.Compared with traditional technology,OLED have excellent characteristics of ultra-light,ultra-thin,ultra-soft,ultra-clear,and ultra-low power consumption,which have an irreplaceable position in various display devices and solid-state lighting.In recent years,a large number of blue material molecular structures have been designed and developed,but blue and deep blue materials with high efficiency and excellent stability are still scarce.It is necessary to develop deep blue and blue fluorescent materials with excellent performance.In the blue light material system,phenanthrimidazole and its derivatives are used as the building block to provide more research directions for researchers in various fields.Phenanthimidazole is a classic skeletal structure building group.Because of its rigid large plane,high degree of conjugation and unique structure,its easy modification degree has become a research hotspot in the design of preparing bipolar,high-performance deep blue materials.When the cyano group is connected to a saturated carbon atom,it becomes a good acceptor unit due to the greater electronegativity of nitrogen and the existence of greater conjugation effect.Carbazole has good hole transport ability.In this paper,combining the advantages of the three groups,we designed and synthesized a new dark blue fluorescent material with phenanthroimidazole as the skeleton,including meta-cyanophenyl structure and carbazole structure,and systematically studied the relationship between its structure and properties.This paper specifically contains the following content:(1)The development and current results of OLED were elaborated,and the device structure and light-emitting mechanism were clearly introduced.The molecular structure and properties of phenanthroimidazole and its derivatives and the research progress and development direction of phenanthroimidazole blue fluorescent materials are described in detail.At the same time,the properties of meta-cyanophenyl introduced into molecular design are summarized.Based on the research of the above groups,the design concept of this paper is finally put forward.(2)3,5-bis(9H-carbazol-9-yl)benzaldehyde complete the synthesis through lithiation and nucleophilic substitution reaction,and then use the"one-pot method"synthesis principle,through Debus-Radziszewski reaction,design synthesized CT-type phenanthrimidazole derivative m DCCPPI,as the skeleton with phenanthrimidazole,benzonitrile group with meta-cyano group as its N1 substitution group,and3,5-bis(9H-carbazol-9-yl)benzaldehyde as C2 substitution.(3)By introducing a benzene ring substituent at the C2 position,based on the m DCCPPI molecular structure,a phenanthrimidazole derivative with a longer skeleton structure was designed and synthesized.3',5'-bis(9H-carbazol-9-yl)-[1,1'-biphenyl]-4-carbaldehyde was completed the synthesis by Suzuki cross-coupling reaction,and pure CT was synthesized by the same Debus-Radziszewski reaction Type phenidimidazole derivative m DCBCPPI.(4)The two compounds were characterized by NMR spectroscopy and mass spectrometry respectively.In addition,through front-line orbital simulation,time-dependent density functional theory calculations,and NTOs,the electronic configuration and molecular excited state are studied,and their photophysical properties,electrochemical properties and thermal stability properties are analyzed.The results of the study show that after adding m-cyanophenyl to the N1 position of phenanthrimidazole,a CT state characteristic molecule is constructed.The natural transition orbit calculation shows that the holes and electrons in the excited state are completely separated,which intensifies the characteristics of the pure CT state molecule.The pseudo-halogen properties of the cyano group give the molecule a low-temperature long afterglow effect.The thermal decomposition temperatures of m DCCPPI and m DCBCPPI are 490°C and 470°C,respectively,and they have good thermal stability.The cyclic voltammetry curves all show a reversible oxidation-reduction process,indicating that the electrochemical performance is stable,which provides a guarantee for the practicability of the fabricated device,and is in line with our design expectations.(5)The non-doped device A prepared with m DCCPPI as the light-emitting layer has the maximum emission peak of the electroluminescence spectrum at 432 nm,showing deep blue emission,with CIE coordinates(0.16,0.07).The turn-on voltage(V_on)is 3.9 V,and the maximum brightness(L_max)reaches 253 cd m^-2,the maximum current efficiency(?_C,max)reached 0.79 cd A^-1,the maximum power efficiency(?_p,max)reached 0.66 lm W^-1,and the maximum external quantum efficiency(?_ext,max)was 1.07%.The non-doped device B prepared with m DCBCPPI as the light-emitting layer,the electroluminescence spectrum showed the largest emission peak at 448 nm,showing deep blue emission,CIE coordinates(0.13,0.08).the turn-on voltage(V_on)is 3.3V,and the maximum brightness(L_max)is 1425 cd m^-2,the maximum current efficiency(?_C,max)is 2.73 cd A^-1,the maximum external quantum efficiency(?_ext,max)is 3.74%,and the maximum power efficiency(?_p,max)reaches 2.31 lm W^-1.The electroluminescence performance study showed that the device showed better electroluminescence performance after introducing a benzene ring at the C2 position of the m DCBCPPI skeleton due to the increase in the degree of conjugation.