Desigin,synthesis And Photophysical Properties Of Organic Room-Temperature Phosphorescent Materials Based On Iminodibenzyl Or Indolocarbazole Moieties

Recently,organic phosphorescent materials have become a research hotspot due to their unique properties,such as easy structure regulation,long luminescence lifetime,large Stokes shift,low biological toxicity and the ability to prepare flexible devices,etc.They have broad application prospects in various fields,such as biological and chemical sensing,information anti-counterfeiting and encryption,and display and lighting,etc.However,traditional organic phosphorescence can only be observed under low temperature and inert solvent conditions.Due to their small heavy-atom effect,weak inter-system crossing and strong non-radiative decay such as thermal deactivation,as well as the quenching effect of water and oxygen,it is difficult to observe organic phosphorescence at ambient conditions.In recent years,more and more rational design strategies to achieve the organic room temperature phosphorescent materials have been reported,and the major research directions include the balance of high efficiency and long lifetime,as well as tunable colors and dual emission properties.Thermally activated delayed fluorescence（TADF）is expected to obtain a long emission lifetime comparable to that of phosphorescence due to the reverse intersystem crossing process,and the combination of delayed fluorescence and phosphorescence can lead to temperature-responsive afterglow color changes,which can broaden the application scope of materials.In order to prepare organic room temperature phosphorescent materials with dual emission of RTP and TADF,in this thesis,we designed and synthesized a series of iminodibenzyl（IDB）or indolocarbazole-based phosphorescent materials and investigated their photophysical properties.The main research contents are as follows:1.Design,synthesis and room temperature phosphorescent property of iminodibenzyl derivativesAs a cheap and readily available electron-rich compound,iminodibenzyl（IDB）can act as a donor in the donor-acceptor（D-A）structured compound.Specifically,the twisted and rigid structure of IDB moiety can suppress non-radiative decay and achieve long-lifetime emission,which is more conducive to the dual emission of RTP and TADF.Moreover,the luminescent properties of this structure can be easily tuned by changing its substituents.Based on this,we designed and synthesized a series of IDB-based D-A structured compounds to study their photophysical properties.We further adjusted the substituent groups to enhance the effect of D-A structure and studied the impact of different substituent groups on their photophysical properties.After that,we introduced benzene moiety as a spacer to the D-A structure to reduce the orbital overlap of HOMO and LUMO,further reducing the energy gap between singlet and triplet excited states.Considering the differences in luminescence properties when donors and acceptors were positioned in the ortho and para positions,we hoped to achieve ultra-long organic room temperature phosphorescence through the richer space charge transfer（SCT）in the ortho structure.The results showed that IDB donor could indeed reduce the energy gap and promote intersystem crossing,thus the IDB derivatives could achieve stronger room temperature phosphorescence.And the introduction of benzene spacer has also successfully reduced the energy gap,so that the molecules of the D-B-A structure could obtain better RTP properties.Due to the obvious difference in fluorescence and afterglow colors,the synthesized p-IDB-BP and p-（OCH₃）₂-IDB-BP are expected to serve as anti-counterfeiting labeling.2.Design,synthesis and photophysical property study of phosphorescent materials based on indolocarbazole derivativesMost recently,our group have exploited a new phosphorescent molecular skeleton Ben-H,and designed and synthesized circularly polarized room temperature phosphorescence material Ben-C18 with both circularly polarized luminescence（CPL）and room temperature phosphorescence properties（Ben-C18）through effective self-assembly strategy of meso-phosphorescent molecules to induce CPL.To study the effects of chain length on the photophysical and self-assembly properties of this kind of compounds,we introduced dodecyl by N-alkylation reaction and added halogen atoms into the organic skeleton to synthesize new derivatives Ben-C12,and compared their photophysical properties with those of Ben-C18.The results showed that the length of the carbon chain had a critical impact on their photophysical properties.Due to the evident reduction in the carbon chain length,the molecular stacking of Ben-C12 became less dense,and the long-lived luminescence intensity was greatly reduced.And Ben-C12 could only form a rod-like morphology after self-assembly,which was completely different form the regular chiral nano-helical fibers of Ben-C18.Fortunately,due to the wide range of luminescent color variations of Br-Ben-C12 over temperature,it could be used for multi-level anti-counterfeiting encryption and visual temperature detection.