类富勒烯团簇发光性能的理论研究  

First-principles study of luminescence of fullerene-like clusters

作　　者：杨小伟 佘洁 周思 赵纪军[1] Yang Xiao-Wei;She Jie;Zhou Si;Zhao Ji-Jun(Key Laboratory of Materials Modification by Laser,Ion and Electron Beams(Dalian University of Technology),Ministry of Education,Dalian 116024,China)

机构地区：[1]大连理工大学三束材料改性教育部重点实验室,大连116024

出　　处：《物理学报》2022年第12期21-29,共9页Acta Physica Sinica

基　　金：国家自然科学基金(批准号:11974068,91961204)资助的课题。

摘　　要：热激活延迟荧光(TADF)作为一种特殊的分子荧光机制,对于提高发光效率有着重要意义.以C_(60)和C_(70)为代表的碳富勒烯具有高对称结构和离域π电子,被广泛证明具有显著的TADF效应;相比之下,其他类富勒烯团簇的光物理性质尚不清楚.本文利用含时密度泛函理论探索了一系列类富勒烯团簇的激发态性质,包括实验合成的具有不同尺寸的氮化硼笼型团簇B_(12)N_(12),B_(24)N_(24)和B_(36)N_(36),以及与B_(12)N_(12)结构相同、元素组成不同的B_(12)P_(12),Al_(12)N_(12)和Ga_(12)N_(12).计算结果表明,这些类富勒烯化合物团簇具有2.83—6.54 eV的能隙,主要吸收紫外光,荧光发射波长在可见光区间,包括红光、橙光、蓝光和紫光.它们的第一激发单重态和三重态的能量差较小(ΔEST<0.29 eV),因此可能通过系间窜越和反系间窜越发生TADF过程.导致ΔEST较低的原因是这些化合物团簇的最高占据分子轨道和最低未占据分子轨道分布在不同的元素上,使得二者重叠度较低.这些理论结果揭示了类富勒烯团簇的发光性质和可能的荧光机理,为寻找和设计稳定高效的发光材料提供了重要指导.Thermally activated delayed fluorescence(TADF),a unique molecular fluorescence mechanism,plays a key role in designing emitters of high efficiency.Carbon fullerenes such as C_(60) and C_(70) exhibit strong TADF with intensity even higher than that of the prompt fluorescence,owing to their long lifetimes of triplet state and modest singlet-triplet energy gaps.Thus,there arises the intriguing question whether other fullerene-like clusters can also have fluorescence and host the TADF effect.In this work,by time-dependent density functional theory(TD-DFT)calculations,we explore the excited-states of the experimentally reported boron nitride cage clusters B_(12)N_(12),B_(24)N_(24) and B_(36)N_(36),as well as compound clusters B_(12)P_(12),Al_(12)N_(12) and Ga_(12)N_(12) with the same geometry as B_(12)N_(12).Using the HSE06 hybrid functional,the predicted energy gaps of these fullerenelike clusters are obtained to range from 2.83 eV to 6.54 eV.They mainly absorb ultraviolet light,and their fluorescence spectra are all in the visible range from 405.36 nm to 706.93 nm,including red,orange,blue,and violet emission colors.For the boron nitride cages,the energy gap of excited states increases with the cluster size increasing,accompanied by a blue shift of emission wavelength.For the clusters with B12N12 geometry and different elemental compositions,the excited energy gap decreases as the atomic radius increases,resulting in a red shift of emission wavelength.In addition,the highest occupied molecular orbitals(HOMOs)and lowest unoccupied molecular orbitals(LUMOs)of these compound cage clusters are distributed separately on different elements,resulting in small overlap between HOMO and LUMO wavefunctions.Consequently,these fullerenelike clusters exhibit small singlet-triplet energy differences below 0.29 eV,which is beneficial for the intersystem crossing between the excited singlet state and triplet state,and hence promoting the TADF process.Our theoretical results unveil the fluorescence characteristics of cage clusters ot

关 键 词：类富勒烯团簇 激发单重态 激发三重态 荧光 反系间窜越 热激活延迟荧光 

分 类 号：O641.4[理学—物理化学] TB34[理学—化学]