Design,Synthesis And Performance Research Of Chiral Luminescent Materials Based On Binaphthyl Units And Cyclometallated Platinum Complexes

Circularly polarized light(CPL)can be directly generated by Chiral luminescent materials under optical or electrical excitation,which has attracted great interests in Organic Light-Emitting Diodes(OLEDs).After more than two decades of development,Organic Circularly Polarized LightEmitting Diodes(CP-OLEDs)based on chiral luminescent materials have made great progress.However,limited by the efficiency of the device and the purity of circularly polarized electroluminescence,CP-OLED still needs to make further breakthroughs on the road to commercialization.To explore the relationship between the structure and properties of organic chiral luminescent materials,focusing on molecular structures,we designed a pair of chiral luminescent materials with axial chiral conformation based on chiral binaphthyl unit,named R/S and a series of chiral liquid crystal cyclometalated platinum complex-based luminescent materials respectively.The structures of the compounds were confirmed by hydrogen and carbon NMR spectroscopy,time-of-flight mass spectrometry;The properties of the materials were discussed in detail by Thermogravimetric Analysis,Uv-Vis,Steady/Transient Fluorescence Spectroscopy,Differential Scanning Calorimetry,Circularly Polarized Luminescence Spectroscopy and Cyclic Voltammetry.Solution-processed CP-OLEDs devices were prepared with these materials as dopants for light-emitting layer,the electroluminescence properties were studied.The main findings are as follows:(1)Taking the axial binaphthyl unit as center,thiophenol units was introduced on its two wings,a series of chiral diphenyl sulfone derivative acceptors was constructed;the donor unit acridine was connected to the periphery of the diphenyl sulfone derivative to form a pair of blue chiral luminescent molecules/R/S-DPS-Ac,and the relationship between their structures and properties was explored in detail.Results showed that the temperature of the two compounds was above 400℃ when the thermal weight loss was 5%,showing good thermal stability;the two compounds both exhibited blue light emission in solution and films,and the maximum emission wavelength were 470 nm;Strong CPL signals were detected in toluene solution.Solution processed CP-OLEDs were prepared using the two compounds as dopants for light-emitting layer.The device based on compound S showed better performance,with a maximum EQE of 2.91%.With further study on their circularly polarized electroluminescent properties,a stable CPEL signal was detected and the gEL value was 1.74×10-3.(2)The cyclometallated platinum complex was used as the luminescent centers,the mesogenic units was introduced into its auxiliary ligand to promote the formation of liquid crystal phase;two or four chiral carbon centers were introduced into the cyclometallated ligand,respectively.Two chiral liquid crystal cyclometallated platinum complexes C2 and C4 were designed and synthesized to explore the effect of the number of chiral centers and the liquid crystal properties on the luminescent properties.The results showed that:complex C2 exhibited obvious chiral nematic liquid crystal texture observed by polarizing optical microscope during the cooling process,while C4 did not show liquid crystal behavior;complexes C2 and C4 both showed good luminescent efficiency with PLQY of 76.4%and 79.3%,respectively;due to the regular alignment order of the liquid crystal,the enhanced CPL signal of complex C2 was detected in the annealing film compared with that in the neat film,and its circularly polarized luminescence asymmetry factor was amplified 10 times,no obvious CPL signal was detected for C4 in neat film;solution-processed CP-OLED devices were prepared using complexes C2 and C4 as dopants for light-emitting layer,and the devices based on C2 showed strong CPEL signal with gEL value of 5×10-3;the maximum EQE reached 18.01%,and the C4-based device showed a weak CPEL signal with gEL value of 9 × 10-4,the maximum EQE was 8.89%.(3)In order to solve the decrease of circularly polarized optical purity caused by the racemization of the chiral center during the synthesis,we changed the position of the chiral center on the basis of molecules C2 and C4,to better construct liquid crystal molecules,we reduced the number of chiral alkyl chains to improve the regularity of the molecule,two chiral liquid crystal cyclometallated platinum complexes D1 and D2 were designed and synthesized,the influence of chiral center and liquid crystal properties on the luminescent properties were further explored.The results showed that the two complexes both exhibited liquid crystal properties,and both smectic and chiral nematic textures were observed during the cooling process;complexes D1 and D2 showed excellent luminescent efficiency with PLQY of 84.8%and 78.4%,respectively;the CPL signals of D1 and D2 were significantly enhanced after the neat films were annealed;Using D1 and D2 as dopants for light emitting-layer,solution-processed CP-OLEDs devices were prepared,the devices based on the two complexes were detected strong CPEL signals.The maximum EQE of the D1-based device reached 15.34%with gEL value of 5 × 10-3,and the maximum EQE of the D2-based device was 15.11%with gEL value of 9×10-3.