Design,Synthesis And Properties Of Pure Organic Room Temperature Phosphorescent Materials With A High Level Of Lifetime-Efficiency Balance

Compared with traditional inorganic and metal complex phosphorescent materials,pure organic room temperature phosphorescent materials have significant advantages in terms of cost,biocompatibility,structural flexibility,structural processability and stability.And it has broad application prospects in lighting,biological imaging,stress/chemical sensing,optical encryption and anti-counterfeiting.However,because triplet excitons are easily dissipated by molecular thermal vibration and quenched by triplet oxygen,room temperature phosphorescence(RTP)is considered to be the residual of low temperature phosphorescence(LTP)after molecular thermal vibration dissipation and oxygen quenching.At the same time,pure organic molecules usually have a relatively small spin-orbit coupling(SOC)constant,and the rate of intersystem crossing(ISC)is relatively low.After ultraviolet/visible light excitation,the probability of excitons crossing from the singlet state to the triplet state is relatively low,making it more difficult to obtain RTP materials with a high level of balance of lifetime-efficiency.In this article,we designed and synthesized a series of isomers by introducing heavy atom Br and cyano(-CN)/amide(-CONH2)into commercially purchased carbazole(CCZ).Due to the isomer effect,after each molecule forms a crystal,its intermolecular force and stacking mode will be significantly different.Through our reasonable design and synthesis,we have obtained:(1)High-level balanced lifetime-efficiency pure organic room temperature phosphorescent materials with an efficiency of 44.0%,lifetimes of 316.8 ms and an efficiency of 34.8%,lifetimes of 342.3 ms;(2)The ratio of fluorescence and phosphorescence emission peaks can be adjusted by simply changing the excitation wavelength.To achieve white light emission with a color coordinate of(0.32,0.34);(3)Under the action of external mechanical force,and accompanied by bright long afterglow,mechanophosphorescence material can be used as an alternative material for stress sensing.At the same time,we have also synthesized laboratory-synthesized carbazole(LCZ)and its derivatives,and further used low temperature,degassing,polymer blending and other characterization methods to prove that the LCZ derivative materials which designed and synthesized by us are not weaker than Intrinsic phosphorescence of CCZ derivatives;Strong molecular interactions between LCZ derivatives do not effectively stabilize triplet excitons;The weak room temperature phosphorescence of LCZ derivatives is due to molecular thermal inactivation;and the excellent room temperature phosphorescence properties of CCZ derivatives are caused by the synergistic effect of trace isomer(benzoindole derivatives)with the host.We think,an excited guest interact with numerous excited hosts to form the local excited states.Charge and/or energy transfers will no longer be limited between one guest and one or a few hosts,and the formed oversized space charge transfer states enhance the guest-host interactions and block the thermal inactivation and stabilize the triplet states.In summary,the CCZ derivatives involved in this article have potential applications in lighting,biological imaging,and stress sensing.At the same time,it was proved that excellent room temperature phosphorescence can also be achieved when the LCZ derivative is provided in a rigid environment.The comparison provides a simple and effective strategy to further explore the role of isomer doping in the luminescence process and the luminescence mechanism of CCZ derivatives.