Synthesis And Properties Of Organic Room Temperature Phosphorescent Small Molecules

As a common building block of organic room temperature phosphorescence(RTP)materials,carbazole can provide long-lasting lifetime extension inheritance and excellent electron giving ability.We have focused on promoting system transitions and suppressing nonradiative transitions as the main objective.By introducing different functional groups into carbazole group,we have designed and synthesized a series of organic room temperature phosphorescence small molecules,achieving fine regulation of phosphorescent properties.Our results provide new ideas for the further design of molecules with superior phosphorescent materials in the future.The first chapter introduces the development and luminescence mechanism of room temperature phosphorescent materials in detail.The factors affecting the phosphorescence performance and corresponding optimization schemes are explained,while the application prospects of designing organic room temperature phosphorescent materials in recent years are summarized.Then,the ideas of this thesis are proposed.In Chapter 2,Effect of Aldehydes on Phosphorescent Luminescence Efficiency: The heavy atom effect plays an important role in promoting phosphorescent performance,while too many heavy atoms often leads to phosphorescent quenching.In this chapter,an aldehyde group was introduced into carbazole group containing bromine to improve phosphorescent performance through the n-π* transition and hydrogen bonding provided by aldehyde groups.After the simple formylation reaction,compound CS-89 with room temperature phosphorescence properties was obtained.It was found that the phosphorescence quantum yield of CS-89 was 3.8%,which was approximately 2.5 times of that of CS-88.However,the lifetime of CS-89 was decreased to some extent.Due to the existence of lone pair electrons in oxygen,the energy gap between the single and triple line states was reduced,which significantly increase the inter system transition rate,effectively improving the phosphorescent efficiency.However,due to the strong electron absorption characteristics of aldehyde groups,the electron density of carbazole group was reduced.Therefore,the molecular stacking was relatively loose,thus resulting in the shortened phosphorescent lifetime.In Chapter 3,Improvement of Intermolecular Interaction to Regulate Room Temperature Phosphorescence Properties: Two RTP molecules,coded as CS-90 and CS-91 were obtained by molecular engineering of N-substituted benzene group to avoid the decreaseing of the electron density at carbazole group.The phosphorescence lifetimes of the two compounds was improved compared with the reference compound,especially for CS-91,which exhibited a long room temperature phosphorescence lifetime of 355.8 ms.The analysis of crystal structure and theoretical calculation shows that CS-91 forms a more compact and effective molecular stacking thrgouhg the intermolecular interaction of O-H···π and C-H···π.The spatial configuration of molecules close to the right angle helps to fix the molecular conformation and limit molecular vibration,inhibiting non radiative transition processes.In addition,the electron distribution of the HOMO and LUMO energy levels of the compound exhibits a highly separated form,which is also beneficial for suppressing the decrease in the density of the carbazole electron cloud caused by the conjugation effect.The increase in electrostatic potential difference on the molecular surface provides a theoretical basis for the enhancement of the stacking force.Conclusion,In this thesis,molecular engineering were performed on carbazole derivatives for the purpose of promoting inter system transition processes and suppressing non radiation processes.RTP molecules were characterized through a series of photophysical property tests.Combined with the analysis of single crystal and theoretical calculation results,it was shown that the high luminous efficiency of CS-89 comes from a small single trilinear energy range and a large inter system transition rate and the long room temperature phosphorescence lifetime of CS-91 comes from the ordered and compact molecular stacking.