三种热活化延迟荧光分子单三态能隙差的理论研究
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摘要
基于两个实验报道的热活化延迟荧光(TADF)分子(DPO-TXO2和DDMA-TXO2),通过改变供体基团,理论设计出一种新分子DPPA-TXO2.采用半经典的Marcus理论表达式,以及密度泛函理论和含时密度泛函理论,研究了改变这三个分子供体单元对其TADF机制的影响.研究结果表明,这三个分子的单三态能隙差都极小,仅为0.01或0.02 eV,这确保了从三重态到单重态的反系间窜跃过程的顺利进行.此外,理论预测的DPO-TXO2分子的反系间窜跃速率为5.67×10~5 s~(-1),跟实验测量值(1.04×10~6 s~(-1))非常吻合,并能够与其辐射失活速率(2.79×10~5 s~(-1))竞争.值得注意的是,新设计的DPPA-TXO2分子的反系间窜跃速率也达到了10~3数量级,是一个潜在的TADF发光体.
Based on two experimentally reported thermally activated delayed fluorescence(TADF) molecules(DPO-TXO2 and DDMA-TXO2), we designed a new molecule(DPPA-TXO2) theoretically by changing the donor groups. The semiclassical Marcus theory expression coupled with density functional theory and time-dependent density functional theory were used to explore the effect of donor change on their TADF mechanism. The present studies reveal that the singlet-triplet energy gaps of all the three molecules are rather small(0.01 or 0.02 eV), ensuring the achievement of the reverse intersystem crossing(RISC) process from triplet excited state to singlet excited state. In addition, the RISC rate of DPO-TXO2 is calculated to be 5.67×10~5 s~(-1), which is consistent with the experimentally measured value of 1.04×10~6 s~(-1), leading to the competition with the radiative decay rate of 2.79×10~5 s~(-1). It is worthy to note that the RISC rate of our newly designed DPPA-TXO2 molecule is predicted to be in 10~3 order of magnitude, which is potential TADF emitter.
Based on two experimentally reported thermally activated delayed fluorescence(TADF) molecules(DPO-TXO2 and DDMA-TXO2), we designed a new molecule(DPPA-TXO2) theoretically by changing the donor groups. The semiclassical Marcus theory expression coupled with density functional theory and time-dependent density functional theory were used to explore the effect of donor change on their TADF mechanism. The present studies reveal that the singlet-triplet energy gaps of all the three molecules are rather small(0.01 or 0.02 eV), ensuring the achievement of the reverse intersystem crossing(RISC) process from triplet excited state to singlet excited state. In addition, the RISC rate of DPO-TXO2 is calculated to be 5.67×10~5 s~(-1), which is consistent with the experimentally measured value of 1.04×10~6 s~(-1), leading to the competition with the radiative decay rate of 2.79×10~5 s~(-1). It is worthy to note that the RISC rate of our newly designed DPPA-TXO2 molecule is predicted to be in 10~3 order of magnitude, which is potential TADF emitter.
引文
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[2] VOLZ D,WALLESCH M,FLECHON C,et al.From iridium and platinum to copper and carbon:new avenues for more sustainability in organic light-emitting diodes [J].Green Chemistry,2015,17(4):1988-2011.
[3] BALDO M A,O’BRIEN D F,YOU Y,et al.Highly efficient phosphorescent emission from organic electroluminescent devices [J].Nature,1998,395(6698):151-154.
[4] LAMANSKY S,DJUROVICH P,MURPHY D,et al.Highly phosphorescent bis-cyclometalated iridium complexes:synthesis,photophysical characterization,and use in organic light emitting diodes [J].Journal of the American Chemical Society,2001,123(18):4304-4312.
[5] YANG X,XU X,DANG J S,et al.From mononuclear to dinuclear iridium (III) complex:effective tuning of the optoelectronic characteristics for organic light-emitting diodes [J].Inorganic Chemistry,2016,55(4):1720-1727.
[6] UOYAMA H,GOUSHI K,SHIZU K,et al.Highly efficient organic light-emitting diodes from delayed fluorescence [J].Nature,2012,492(7428):234-238.
[7] SANTOS P L,WARD J S,DATA P,et al.Engineering the singlet-triplet energy splitting in a TADF molecule [J].Journal of Materials Chemistry C,2016,4(17):3815-3824.
[8] SANTOS P L,WARD J S,BRYCE M R,et al.Using guest-host interactions to optimize the efficiency of TADF OLEDs [J].Journal of Physical Chemistry Letters,2016,7(17):3341-3346.
[9] FENG S,WEN K,SI Y,et al.Theoretical studies on thermally activated delayed fluorescence mechanism of a series of organic light-emitting diodes emitters comprising 2,7-diphenylamino-9,9-dimethylacridine as electron donor [J].Journal of Computational Chemistry,2018,39(31):2601-2606.
[10] LEE C,YANG W,PARR R G.Development of the Colle-Salvetti correlation-energy formula into a functional of the electron density [J].Physical Review B,1988,37(2):785-789.
[11] MIEHLICH B,SAVIN A,STOLL H,et al.Results obtained with the correlation energy density functionals of Becke and Lee,Yang and Parr [J].Chemical Physics Letters,1989,157(3):200-206.
[12] BECKE A D.Density-functional thermochemistry.III.The role of exact exchange [J].Journal of Chemical Physics,1993,98(7):5648-5652.
[13] FRISCH M J,TRUCKS G W,SCHLEGEL H B,et al.Gaussian 09 [CP].Revision A.02,Wallingford CT:Gaussian,Inc.,2009.
[14] TE VELDE G,BICKELHAUPT F M,BAERENDS E J,et al.Chemistry with ADF [J].Journal of Computational Chemistry,2001,22(9):931-967.
[15] MARCUS R A.On the theory of oxidation-reduction reactions involving electron transfer [J].Journal of Chemical Physics,1956,24(5):966-978.
[16] SAMANTA P K,KIM D,COROPCEANU V,et al.Up-conversion intersystem crossing rates in organic emitters for thermally delayed fluorescence:impact of the nature of singlet vs triplet excited states [J].Journal of the American Chemistry Society,2017,139(11):4042-4051.