Study On D-A Type Organic Room-temperature Phosphorescence

As well known,the creation and application of nobel materials has greatly changed the way human beings life and promoted social advancement.Among them,organic photoelectric materials are widely used in visible light catalysis,biological imaging,solar cells,and flexible screen displays because of their high luminescent efficiency,low power consumption,fast response,full luminescent color,long lifetime,and easy film formation on a large area.The study of the excited states of organic photoelectric materials has always been the focus of attention,especially the process of excited state relaxation is.The room temperature phosphorescent(RTP)material endow long lifetime,due to the spin-forbidden transition between the singlet and the triplet states.However the organic small molecule have low spin-orbit coupling and the fast non-radiative decay,setting great obstacles for developing RTP materials.In this project,we utilize the intramolecular triplet-triplet energy efficient transfer to separate the triplet generation center from the luminescent center,allowing both fast intersystem crossing and slow triplet radiative decay processes,and to develop RTP material with persistent lifetime and high efficiency.Here,we have selected carbazole as electron donors(D)for its high quantum yield and stability,and oxidized dibenzothiophenes as electron acceptors(A)with strong electron-withdrawing ability to construct organic phosphorescent materials with D-A structure.The methylation of the carbazole group is used to adjust the spatial configuration of the D-A structure.For D-A molecules without methyl group,there have different ?EST of the intersystem crossing and stability of the triplet excitons due to the varied molecular configuration and structure,resulting in a huge difference in the luminescence properties.Through photophysical analysis,we found that in solid state,the D-A structure promotes intersystem crossing.Through the investigation of single crystal structures,the influence of molecular configuration and crystal packing on D-A has been figured out.It is found that H-aggregation allows the system to have a more stable triplet state,and J-type packing brings good charge-transfer(CT)state transition.According to theoretical calculations,the related specific transitions between HOMO and LUMO are recognized.The thermal stability of the compounds was analyzed by thermogravimetric and differential thermal analysis.The D-A compounds with methyl groups are found to have weak phosphorescence and favorable for the formation of the CT states.Through single crystal structure analysis,we found that the existence of methyl groups largely changes the spatial molecular and crystal packing.Through theoretical calculations,we verified the existence of methyl groups,is more effective to the formation of CT states.