The Property Research Of Thermally Activated Delayed Fluorescent And Room-Temperature Phosphorescent Materials Based On Supramolecular Interactions

Recently,organic solid-state luminescent materials have been widely applied in electroluminescence,optical waveguides,bio-imaging,sensors due to their convenient design methods and easy fabrication ways,and have been received lots of remarkable results.The emergence of delayed fluorescent materials and phosphorescent materials attracts much attentions of researchers even further.In the initial design methods for delayed fluorescent materials and phosphorescent materials,researchers tended to disclose the relationships between molecular structures and properties,and then designed luminescent materials with high performances by optimizing molecular structures.Among these investigations,researchers summarized many material design experiences,such as introducing donor-acceptor structure for a small energy gap between single excited state and triplet excited state,accelerating spin-orbit coupling by introducing heavy atoms,and accelerating intersystem crossing process by introducing substituents with lone pair electrons.With the development of delayed fluorescent materials and phosphorescent materials,researchers concluded that the photophysical properties of these materials could be influenced not only by molecular structures,but also by aggregation structures and supramolecular interactions.Hence,further investigation of the relationship between supramolecular interactions and properties of triplet-involved luminescent materials is the key factor for the breakthrough of photophysical properties.In this dissertation,supramolecular interactions were chosen to adjust aggregation behaviors,achieving a series of thermally activated delayed fluorescent(TADF)materials and room-temperature phosphorescent(RTP)materials.By the concise adjustment of supramolecular interactions,we also changed the photophysical properties and mechanical properties of these triplet-involved luminescent materials.This dissertation also explored the potential application values of these materials,the major research contents are listed as follows:1.In chapter ?,we designed four compounds named 1a,1b,2a and 2b,which are all non-emissive in single molecule state.However,in crystalline state,1a and 1b could emit bright TADF emission.Crystal structures and theoretical results proved that TADF behaviors could be assigned to the supramolecular chains which are formed by hydrogen bonds.In single molecule state,excited-state conformation is twist and radiates energies by non-radiative transition.Differently,in crystalline state,supramolecular chains would restrict the formation process of excited state,forming an excited-state conformation which is different from the one in single molecule state and radiates energies by radiative transition.Without supramolecular chains,the excited-state conformations in crystals 2a and 2b would be the same as those in single molecule state,resulting the non-emission of crystals.Based on such evidences,we proved that crystalline-induced TADF emission was caused by excited-state conformation capture.2.In chapter ?,we successfully achieved the transformation of TADF materials to RTP materials with afterglow.Firstly,based on the molecular structure of 1b,we achieved the change of photophysical property from TADF to RTP emission by introducing Br atoms.Experimental results and theoretical calculations proved that Br atoms could enhance intersystem crossing and make T1 state as dominant excited state,achieving RTP emission,and that the strong aggregation effect induced by supramolecular chains may impair RTP emission.Next,based on the skeleton of 1,the hydrogen atoms on nitrogen atoms were replaced with phenyl rings,which may enlarge the distance between two neighboring molecules and reduce the aggregation effect,thus compound 4 was designed and synthesized,proving that a suitable aggregation effect may benefit RTP emission.Finally,?…? stacking,which is used to stabilize triplet excitions and capture excited-state conformations,and Br atom,which is usually introduced for an enhancement of triplet excitons,were employed for the construction of ultra RTP material 5.3.In chapter ?,we achieved organic phosphorescent polymorphs with stimuli-responsive single/dual phosphorescent switching.BrTA-F was designed by changing the position of F atoms based on the molecular structure of 3 in chapter ?.By solvent method or vacuum deposition,Cry-A displaying single RTP emission and Cry-B displaying dual RTP emission were obtained.Crystal structures proved that these two polymorphs both have supramolecular chains,which could help the achievement of RTP emission,and that F atoms could form different halogen bonds with other molecules,achieving single/dual polymorphs.Experimental results combined with theoretical calculations revealed that the generation of dual RTP could be ascribe to the different types of Sn and Tn transition forms and the large energy gap between T2 and T1.Furthermore,two polymorphs could transform to each other by heating or the treatment of solvent vapor,which is known as the first report about pure organic thermal-induced dual RTP switching.Finally,by using AND gate and OR gate,we proved the potential application of BrTA-F polymorphs in stimuli-responsive material fields.4.In chapter ?,we designed crystal DBBZL with controllable elastic and plastic bending,and proved the potential application values in optical waveguiding field.For photophysical properties,?…? stacking could capture excited-state conformation for RTP emission but the effect of Br atoms is limited.Interestingly,?…? stacking and Br atom construct an intermediate region structure between anisotropic packing and isotropic packing which endows DBBZL with controllable elastic and plastic bending.In elastic bending process,?…? stacking could provide a structural buffering unit for deformations.In plastic bending process,Br…Br interactions and C-H…Br interactions would be broken and re-formed,leading the relative slip of bending face.Finally,taking advantages of the high flexibility and phosphorescent emission,the first report about flexible optical waveguides of large phosphorescent crystals was realized.In summary,we achieved a series of TADF materials and RTP materials on the aspect of supramolecular interactions,proving the relationship between aggregation effect and the photophysical properties of luminescent materials.Simultaneously,some of the RTP materials in this dissertation also possess stimuli-responsive property or flexible property,further proving the importance of supramolecular interactions for the mechanical properties of luminescent materials.The results of this dissertation not only provide new thinking ways for the investigations of the relationship between triplet-involved materials' properties and aggregation effect,but also shed deep light on multi-functional triplet-involved emission materials.