| Since the invention of Organic Light-Emitting Diodes(OLEDs)in 1987,it has self-luminous,low-voltage driving,light and thin,wide viewing angle,fast response,flexible folding,simple preparation process and low cost.It can be produced in a large area and has a broad application prospect in the field of full color display and solid state lighting.At present,highly efficient and stable blue organic electroluminescent materials and devices are relatively scarce compared to existing red and green organic electroluminescent materials and devices.The blue light material itself has a wide energy gap,so it is difficult to obtain a blue light device with low voltage,high efficiency,and good stability.Therefore,the development of efficient and stable blue light materials and devices is critical to the commercialization and application of OLEDs.The work of this thesis is to design and develop new and efficient blue organic fluorescent materials and explore the performance of their OLED devices.The content of this paper mainly includes the following three parts.The first part introduces the historical background,luminescence principle,device structure,performance parameters and material categories of organic electroluminescence.The retarded blue light materials in the new generation of organic light-emitting materials,such as TADF blue light materials,HLCT blue light materials,and TTA blue light materials,are highlighted.Finally,the significance and work of the topic of this thesis are expounded.In the second part,a series of new blue luminescent materials were developed for the reasonable molecular modification of the bisanthracene(BD)blue organic luminescent materials reported by the predecessors,and the relationship between their structure and properties was systematically studied.Successfully prepared high efficiency blue OLED devices.The details are as follows:1)Two target molecules BD1-PMe and BD1-POMe are designed and synthesized by introducing a methyl group or a methoxy group at the para position of the phenyl ? bridge chain at the center of the BD1 molecule.The single crystal structure analysis shows that compared with BD1,the two anthracenes units in the BD1-PMe and BD1-POMe molecules have a larger twist angle with their adjacent benzene rings,which is beneficial to weaken the ?-? stacking between molecules.,thereby improving the luminous efficiency and color purity of the device;2)designing and synthesizing two DA type target molecules BD3-PMe and BD3-POMe by introducing a methyl group or a methoxy group respectively at the para position of the central phenyl ? bridge chain of the BD3 molecule.DFT theoretical calculation predicts that the introduction of methyl or methoxy groups is beneficial to increase the torsion angle between two anthracenes units in the molecule and their adjacent benzene rings,and weaken the ?-? stacking effect between molecules.OLED device research shows that BD1-PMe molecules can be used as host luminescent materials to achieve high-efficiency deep blue nondoped devices(EQE:2.35%;CIE:0.15,0.06),and can also be used as guest luminescent materials to achieve high-efficiency sky blue devices.In summary,from the point of view of the performance of the device,the introduced methyl group is better than the methoxy group,it may be related to a lone pair of electrons on the oxygen of the methoxy group.The third part,based on the first work,can effectively weaken the intermolecular ?-? stacking by increasing the twist angle between the anthracene unit and its adjacent benzene ring.We have also constructed a series of curved molecular modules,which not only solve the tedious and low yield of the first work,but also effectively inhibit the ?-? stacking between molecules and improve the efficiency of the device.The specific embodiment is as follows:In this section,we introduce two anthracenes illuminating units at the meta position of the central ? bridge chain benzene ring,and suppress the intermolecular ?-? by increasing the twist angle between the anthracene unit and the benzene ring.To producing highly efficient non-doped blue light devices.The results of the DFT theoretical calculations are consistent with our expected.Among them,based on the BD3-MH device,the preparation of deep blue non-doped devices was successfully realized,the maximum EQE was 3.65%,and the CIE coordinates were(0.16,0.13).Interestingly.BD3-MH only changes the connection position of the anthracene unit compared with BD3,but the performance is greatly improved.The BD3-based device cannot realize the preparation of undoped deep blue light device due to the intermolecularity in the device.The peak of the exciplex appeared due to ?-? stacking,which seriously affected the color purity,but in the BD3-MH based device,the peak of the exciplex was not found.This also strongly validates our design philosophy.The fourth part,based on the concept of the front of two works:weakening the phenomenon of fluorescence quenching caused by the ?-? stacking between molecules,and also drawing on the reports of related ? bridge chains,we designed and synthesized a series of target molecules.The specific implementation process is as follows:We use a semi-conjugated 5 bridge chain to replace the full conjugated ?bridge chain in the first two jobs.Since the ? bridge chain is sp3 hybrid,it is a regular tetrahedral structure,and this staucture can effectively inhibit the ?-? stacking between molecules,and can effectively improve the efficiency and color purity of the device.The target molecule is constructed by connecting two anthracenes light-emitting units at both ends of the ?bridge.The DFT theoretical calculations show that the results are consistent with our expectations.The target molecules BD1-?-2H and BD1-?-2CF3 were successfully prepared by the final Suzuki coupling reaction using a reasonable design route.From the results of photophysical data,we found that the emission spectrum of BD1-?-2CF3 is blue-shifted compared with BD1-?-2H in toluene solution;in the film emission peaks of dimer of BD1-?-2H is discovered,but BD1-?-2CF3 not find a peak of the dimer.It is shown that CF3 introduced on the 8 bridge chain can better inhibit the ?-?stacking between molecules with respect to H.Therefore,we used BD1-?-CF3 to prepare the device,and successfully prepared an nondoped blue light device.The maximum EQE was 3.26%,the CIE coordinate was(0.15,0.11),and there was a slight efficiency roll-off.Therefore,the use of a semi-conjugated ? bridge chain can effectively inhibit the ?-? stacking between molecules and realize the preparation of highly efficient nondoped blue OLED devices,which is important reference meaning for the design and development of novel nondoped blue-light material molecules. |
PDF Full Text Request