Circularly Polarized Organic Optoelectronic Functional Materials : Design,Synthesis And Applications

In recent years,organic optoelectronic functional materials with circularly polarized luminescence（CPL）have achieved increasing attentions and become a new research hotspot in the field of luminescent materials owing to their wide potential applications in optical quantum information,optical spintronics,chiral sensing,bioimaging,optical data storage,3D display.CPL refers to the phenomenon that light-emitting systems selectively emit differentially left-and right-handed circularly polarized light.Currently,the research on CPL optoelectronic functional materials mainly includes chiral metal complexes,small molecules,polymers and supermolecules,etc.The luminescence process of CPL organic optoelectronic functional materials is complex and can be divided into circularly polarized fluorescence,circularly polarized phosphorescence,circularly polarized thermally activated delayed fluorescence（CP-TADF）and circularly polarized organic ultra-long room temperature phosphorescence（CP-OURTP）according to different luminescence types.In this thesis,we designed and synthesized chiral red TADF materials,chiral supramolecular room-temperature phosphorescent materials and racemic ionic crystal ultralong room-temperature phosphorescent materials,and conducted a series of structural characterization and performance studies on the obtained materials,as follows.（1）TADF materials have aroused extensive attention due to their excellent optoelectronic properties,and a chiral Donor-Acceptor-Donor（c D-A-D）strategy is proposed in this chapter to design novel chiral TADF materials.By combining chiral and non-chiral intramolecular charge transfer（ICT）,the intramolecular charge transfer and chiral transfer are enhanced,resulting in efficient red CPL emission.Due to the direct involvement of chiral binaphthyl units in TADF emission,the materials exhibit excellent CPL photoluminescence both in solution and the aggregated state,with the photoluminescence asymmetry factor(g_lum)of 2.2×10^-3,which is higher than that reported for chiral binaphthyl luminescent materials prepared by chiral perturbation strategy.Because of the good CPL luminescence,solubility and film-forming properties,they are applied as a luminescent guest in solution-processed circularly polarized organic light-emitting diodes（CP-OLEDs）to achieve orange-red/red circularly polarized electroluminescence with an external quantum efficiency of 2.0%and the electroluminescence asymmetry factor of 2.6×10^-3,whose performances are among the best results of the reported solution-processed orange-red and red TADF CP-OLEDs.（2）Supramolecular assembly has been shown to be an effective strategy for achieving efficient room-temperature phosphorescent materials,and this chapter presents a method for designing chiral supramolecular room-temperature phosphorescent materials to obtain a series of deep blue CPL room-temperature phosphorescent materials.Chirality can be transferred to the whole system through supramolecular assembly with g_lum reaching 2.2×10^-3.Meanwhile,the racemic supramolecular materials were found to exhibit unexpected phosphorescence enhancement with the phosphorescence lifetime of 143.3 ms,which is 9 times higher than that of the chiral supramolecular materials.The systematic study indicates that the racemic supramolecular materials are more likely to form a large number of microcrystalline structures under the same preparation conditions,which inhibit the nonradiative leap process and exhibit superior room-temperature phosphorescence performance.This chapter explores the correlation between room-temperature phosphorescent properties and supramolecular solid types,which provides new ideas for the design of higher performance supramolecular organic room-temperature phosphorescent materials.（3）According to Wallach’s rule,single crystals of racemates are always denser than chiral enantiomers,and racemate-based organic ultralong room-temperature phosphorescent（OURTP）materials tend to exhibit superior properties due to the high dependence of molecular stacking.This chapter proposes a strategy to prepare racemic self-assembled ionic crystal OURTP materials,which benefit from a highly rigid ionic crystal structure where the nonradiative leap process is greatly suppressed,resulting in long phosphorescence lifetime of up to 1.29 s and high phosphorescence quantum efficiency of up to 17.17%.The tightly packed structure in the crystal allows them to exhibit a small single-triplet state energy level difference(ΔE_ST)and exhibit TADF properties.The room-temperature phosphorescence properties are weakened by adjusting the p H of the material either by the external acid or base.Interestingly,the high degree of self-assembly between racemic ions induces unique CPL with g_lum between 0.010 and 0.013.This work in this chapter combines ionic crystals,OURTP,and racemic self-assembly to provide a new strategy for constructing CP-OURTP.