扭曲结构D-A分子的设计、合成及激发态性质研究
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摘要
有机电致发光是目前有机半导体领域的重要研究方向和热点。它的发展经历了两个重要的阶段性突破：一是器件制备从块状晶体到薄膜，另一个是从荧光到磷光金属配合物。层状薄膜器件结构开启了当今有机电致发光研究的起点，而磷光材料在电致发光中的应用则推动了电致发光快速发展。目前电致发光效率和稳定性都已经达到工业化生产的标准，但是磷光材料本身所需的稀有贵重金属（Ir、Pt等）原料限制了其在将来的大规模工业生产中的应用，因而开发新型的有机分子电致发光材料仍有必要。
磷光材料的成功在于其充分利用了电致发光器件中电子空穴复合产生的占75%比例的三线态激子，单线态激子发生系间窜越向更低能级的三线态转移能使磷光器件的激子利用率甚至可以达到100%，正是磷光材料的高激子利用率促使电致发光器件的性能发展到目前的水平。因而如何提高器件的激子利用率则成了设计新型有机电致发光材料的指导思想。
根据量子自旋统计，电致发光器件中电子空穴从两极注入迁移复合会形成25%的单线态激子和75%的三线态激子（一般因跃迁禁阻而不发光）。目前提高器件的激子利用效率通常采用两种方法，其一是利用三线态激子发光（磷光）或者将三线态激子转换成单线态激子发光（延迟荧光，如TTA和TADF），其二是直接打破量子自旋统计的限制让单线态激子的生成比例突破25%。共轭聚合物发光器件中发现单线态激子比例超过25%的实例，一种观点是聚合物的弱束缚态激子在电子空穴复合时单线态激子的生成概率大于三线态，另一种则是相邻的聚合物分子之间形成高能的分子间CT态，CT态的单三线态能级接近，三线态激子发生反系间窜越使单线态激子比例就会超过遵守量子自旋统计的25%。
同聚合物一样，CT激发态也是一种弱束缚激子态，电子空穴会分布在分子内的不同位置或者两个相邻的分子上，之间只有很弱的库伦作用力束缚着。因而利用CT态来发展有机电致发光材料可能成为提高器件的激子利用率的途径。但是受轨道对称性及重叠程度的影响，CT态材料通常发光效率较低。因而如何设计高发光的CT态就成了关键。
扭曲结构D-A分子通过给受体间大的扭曲角抑制或打断两者之间的共轭，可以产生给受体间的电荷转移跃迁。给体采用三苯胺，受体采用常用的高发光生色团，扭曲结构D-A分子可以实现高的发光效率；通过改变受体单元，可以实现扭曲结构D-A分子的不同光色的发光调控；理论模拟计算表明扭曲结构D-A分子给受体间存在较大的扭曲角（约30-70°），前线轨道模拟和电化学测试结果显示，扭曲结构D-A分子HOMO分布在给体三苯胺上，LUMO分布在受体生色团上，同时HOMO和LUMO之间存在一定程度的轨道交叠，这是扭曲结构D-A分子高发光效率的原因；在扭曲角的存在下，D-A分子内的LE（局域态）和CT态发生杂化而生成新的局域电荷转移杂化态（Hybridized Local and ChargeTransfer state，HLCT）；高发光的LE态和弱束缚的CT态杂化而成的HLCT态是一个高发光的CT态；扭曲角的变化对HLCT态的性质影响较大，扭曲角度越大，最低HLCT态中的CT成分越多，扭曲角达到90°，HLCT态中没有LE成分，显示为不发光的纯CT态；溶剂化实验显示HLCT态在低极性（如正己烷溶剂）下显示局域激发态性质，在高极性（如乙腈溶剂）下呈现CT态性质；扭曲结构D-A分子在不同极性溶剂中的单指数寿命曲线确认了HLCT态的存在，而不是LE和CT两个态的混合；理论计算模拟了HLCT态在极性溶剂中的变化，发现HLCT态在低极性下能级下降缓慢，高极性下能级下降很快，与溶剂化实验中观察到的扭曲结构D-A分子在低极性下光谱移动较小而高极性下光谱移动很大的现象相符；HLCT态偶极距在不同极性溶剂中的非线性变化则是扭曲结构D-A分子溶剂化光谱随极性非线性移动的根源。
利用HLCT态性质的扭曲结构D-A分子作为发光层制备的电致发光器件展示了优越的性能，尤其是深蓝光与深红光以及橙光器件的发光效率达到或超过文献报导同类材料的最大值；其电致发光器件的激子利用率经估算均超过了量子自旋统计25%的限制，并最大达到了90%（深红光，TPA-NZP）；器件的发光衰减实验没有观察到明显的长寿命衰减，即基本无延迟荧光；激子利用率的突破可能是弱束缚的CT态杂化而成的HLCT态在器件电注入条件下电子空穴复合直接形成了超过25%比例的单线态激子，即HLCT态单线态激子的形成概率大于三线态激子，也可能是高能CT态单三线态之间的反系间窜越过程使最低单线态激子的比例超过25%；扭曲结构D-A分子内分离的稳定氧化还原态对于提高器件稳定性即寿命有利，器件的高效率高稳定性表明HLCT是下一代电致发光的有效途径。
通过溶液培养或气相沉积方法获得并分析了扭曲结构D-A分子的各种不同的晶体结构及分子堆积方式，如头尾交替平行堆积、平行错位堆积等；在TPA-PY的O型晶体中发现给受体通过各自不同的分子间作用力形成了给受体自分离的堆积方式；通过溶液培养的堆积结构相同的TPA-PY的M型带状晶体和TPA-PE片状晶体成功实现了场效应器件工作并测出其空穴载流子迁移率；通过气相沉积方法生长的TPA-PE片状晶体表明质量更高，场效应器件的空穴迁移率可以达到0.02-0.1cm~2V~(-1)s~(-1)，且器件表现出非常好的稳定性；AFM测试表明气相沉积得到的TPA-PE晶体表面依然不够平整，故迁移率还有可能更高；总体来说扭曲结构D-A分子在高载流子迁移率上有着较大的潜力和研究空间。
The organic light-emitting diodes (OLEDs) as one of the most importantapplications of organic luminescent molecules have been widely studied. In the pastdecades, the rapid development of OLEDs benefited mainly from the emergency oflayered nanoscale-thickness-film device structure and the application of highlyefficient phosphorescent materials. Nowadays, OLEDs have come to the stage ofapplication in industry production, but the cost of rare and expensive heavy metal inphosphorescent materials prevents it for further development in the future.
The performance of OLEDs is ultimately decided by the theoretically attainableradiative excitons ratio for electroluminescence. In phosphorescent device the75%triplet excitions formed in electric condition by spin coupling statistics could beeffectively employed, in many cases, the proportion was nearly100%. If a pureorganic material can fully employ100%excitons like a metal-based phosphorescentmaterial, it is very significant for the development of OLEDs due to their advantage incost and resource. In current stage, some investigations based on delayed fluorescenceby transferring triplet excitons to singlet for employing more than25%excitonsthrough TTA or TADF methods have been reported. In extended pi-conjugatedmolecule or polymer with delocalized electronic state, a breakthrough in the singletexciton ratio was also observed, which is explained by larger singlet formingprobability in weakly binding state or triplet transferring to singlet in the high energyinter-chain CT state. This directs a concept for OLED material design to breakthrough the spin coupling statistics (singlet/triplet=1/3) in strongly bound excited stateby employing molecular exciton state with weak binding energy. Thus to findfluorescent molecules with properties of weakly bound exciton in the lowest excitedstate as well as high fluorescence at the same time would be a route towards thenext-generation highly efficient OLED material design.
Charge-transfer (CT) exciton is a kind of weakly coupling interaction, in whichelectron and hole location sites are separated from and of a certain distance to eachother. The binding energy of CT exciton is supposed be a weak one in betweenWannier exciton (radius of~100, or called free electron and hole) with bindingenergy of~10meV and Frenkel exciton (radius of~10, or call local excited exciton)with binding energy of1eV. But an unavoidable problem for the CT-statephotoluminescence is just its very low quantum efficiency, arising from the forbiddenelectron transition due to the little overlap and poor symmetry of their molecularorbital. Thus to find CT state molecules with high-efficiency fluorescence is of greatimportance currently for improving the highly efficient OLED.
Twisting donor-acceptor molecule is an effective way to obtain the intramolecularCT state by breaking the conjugation between donor and acceptor to induce a CTtransition in between them. Through fixing the donor of triphenylamine andmodifying the acceptor of fluorescent molecular groups, a series of twistingdonor-acceptor molecules with high efficiency and whole-color-range emission canbe obtained. Frontier orbital and electrochemistry results show that, in the twistingdonor-acceptor molecules with twist angles of30-70degree between donor andacceptor, HOMO was localized mainly on triphenylamine and LUMO was localizedon fluorescent molecular groups, with some overlap between them, which isresponsible for the high efficiency of twisting donor-acceptor molecule. The twistconfiguration induces the hybrid of local excited state (LE) and CT state to form anew hybridized local and charge transfer (HLCT) state in the twisting donor-acceptormolecules. The bigger the twist angle is, the more the proportions of CT transitions inHLCT state are. When twist angle reach90degree, the HLCT become a pure CT statewith no light emission, that is, the hybrid of high-efficiency LE state into HLCT statemake it become a highly efficient CT state. HLCT acts as a LE state in the low polarsolvents, and a CT state in the high polar solvents. The single exponential lifetime ofHLCT state in different polar solvents confirm that it is a hybridized state, not amixture of LE and CT states. Theory calculation on the energy level of HLCT state indifferent polar solvents shows that HLCT displays a slow decrease in the low polarsolvents and a large one in the high polar solvents, which is consistent to that of solvatochromic effect of molecular spectra in the experiments. The nonlinear changeof HLCT state dipole is thought to be the root of the special solvatochromic effect oftwisting donor-acceptor molecules in different polar solvents.
OLEDs based on twisting donor-acceptor molecules with HLCT state as emitterexhibit excellent properties, especially in deep-blue, deep-red and orange colordevices, among the best reported results with similar fluorescent color. Almost all thedevices show a breakthrough in the singlet exciton ratio of more than25%(90%inthe TPA-NZP case). The decay of device emission shows nearly none delayed lightwith long lifetime. The breakthrough in the single exciton ratio in twistingdonor-acceptor molecular device is ascribe to the large singlet forming probability ofHLCT state with weak bonding energy, or the triplet transferring to singlet in thepossible inter-or intra-molecular CT state at the high energy level. Moreover, thesimultaneously stable oxidation and reduction in the twisting donor-acceptormolecules contribute much to the lifetime or stability enhancement of OLED device.
Through the solution or PVT (physical vapor transport) methods, various singlecrystal structure and molecular stack mode are discovered for twisting donor-acceptormolecules. In the case of TPA-PY, the self-assembling separately of donor andacceptor is discovered in O crystal. Field effect transistors (FETs) based on slicecrystals of TPA-PE and TPA-PY (M crystal) by solution methods show large holetransporting mobilities. FETs based on TPA-PE crystal by PVT method exhibit higherhole transporting mobilities of0.02-0.1cm~2V~(-1)s~(-1)and great device stability. Atomicforce microscopy measurements show that TPA-PE crystals display poor surfaces,indicating of possible higher mobility in TPA-PE crystal as well as the great potentialof twisting donor-acceptor molecular crystal in the FET area.
磷光材料的成功在于其充分利用了电致发光器件中电子空穴复合产生的占75%比例的三线态激子，单线态激子发生系间窜越向更低能级的三线态转移能使磷光器件的激子利用率甚至可以达到100%，正是磷光材料的高激子利用率促使电致发光器件的性能发展到目前的水平。因而如何提高器件的激子利用率则成了设计新型有机电致发光材料的指导思想。
根据量子自旋统计，电致发光器件中电子空穴从两极注入迁移复合会形成25%的单线态激子和75%的三线态激子（一般因跃迁禁阻而不发光）。目前提高器件的激子利用效率通常采用两种方法，其一是利用三线态激子发光（磷光）或者将三线态激子转换成单线态激子发光（延迟荧光，如TTA和TADF），其二是直接打破量子自旋统计的限制让单线态激子的生成比例突破25%。共轭聚合物发光器件中发现单线态激子比例超过25%的实例，一种观点是聚合物的弱束缚态激子在电子空穴复合时单线态激子的生成概率大于三线态，另一种则是相邻的聚合物分子之间形成高能的分子间CT态，CT态的单三线态能级接近，三线态激子发生反系间窜越使单线态激子比例就会超过遵守量子自旋统计的25%。
同聚合物一样，CT激发态也是一种弱束缚激子态，电子空穴会分布在分子内的不同位置或者两个相邻的分子上，之间只有很弱的库伦作用力束缚着。因而利用CT态来发展有机电致发光材料可能成为提高器件的激子利用率的途径。但是受轨道对称性及重叠程度的影响，CT态材料通常发光效率较低。因而如何设计高发光的CT态就成了关键。
扭曲结构D-A分子通过给受体间大的扭曲角抑制或打断两者之间的共轭，可以产生给受体间的电荷转移跃迁。给体采用三苯胺，受体采用常用的高发光生色团，扭曲结构D-A分子可以实现高的发光效率；通过改变受体单元，可以实现扭曲结构D-A分子的不同光色的发光调控；理论模拟计算表明扭曲结构D-A分子给受体间存在较大的扭曲角（约30-70°），前线轨道模拟和电化学测试结果显示，扭曲结构D-A分子HOMO分布在给体三苯胺上，LUMO分布在受体生色团上，同时HOMO和LUMO之间存在一定程度的轨道交叠，这是扭曲结构D-A分子高发光效率的原因；在扭曲角的存在下，D-A分子内的LE（局域态）和CT态发生杂化而生成新的局域电荷转移杂化态（Hybridized Local and ChargeTransfer state，HLCT）；高发光的LE态和弱束缚的CT态杂化而成的HLCT态是一个高发光的CT态；扭曲角的变化对HLCT态的性质影响较大，扭曲角度越大，最低HLCT态中的CT成分越多，扭曲角达到90°，HLCT态中没有LE成分，显示为不发光的纯CT态；溶剂化实验显示HLCT态在低极性（如正己烷溶剂）下显示局域激发态性质，在高极性（如乙腈溶剂）下呈现CT态性质；扭曲结构D-A分子在不同极性溶剂中的单指数寿命曲线确认了HLCT态的存在，而不是LE和CT两个态的混合；理论计算模拟了HLCT态在极性溶剂中的变化，发现HLCT态在低极性下能级下降缓慢，高极性下能级下降很快，与溶剂化实验中观察到的扭曲结构D-A分子在低极性下光谱移动较小而高极性下光谱移动很大的现象相符；HLCT态偶极距在不同极性溶剂中的非线性变化则是扭曲结构D-A分子溶剂化光谱随极性非线性移动的根源。
利用HLCT态性质的扭曲结构D-A分子作为发光层制备的电致发光器件展示了优越的性能，尤其是深蓝光与深红光以及橙光器件的发光效率达到或超过文献报导同类材料的最大值；其电致发光器件的激子利用率经估算均超过了量子自旋统计25%的限制，并最大达到了90%（深红光，TPA-NZP）；器件的发光衰减实验没有观察到明显的长寿命衰减，即基本无延迟荧光；激子利用率的突破可能是弱束缚的CT态杂化而成的HLCT态在器件电注入条件下电子空穴复合直接形成了超过25%比例的单线态激子，即HLCT态单线态激子的形成概率大于三线态激子，也可能是高能CT态单三线态之间的反系间窜越过程使最低单线态激子的比例超过25%；扭曲结构D-A分子内分离的稳定氧化还原态对于提高器件稳定性即寿命有利，器件的高效率高稳定性表明HLCT是下一代电致发光的有效途径。
通过溶液培养或气相沉积方法获得并分析了扭曲结构D-A分子的各种不同的晶体结构及分子堆积方式，如头尾交替平行堆积、平行错位堆积等；在TPA-PY的O型晶体中发现给受体通过各自不同的分子间作用力形成了给受体自分离的堆积方式；通过溶液培养的堆积结构相同的TPA-PY的M型带状晶体和TPA-PE片状晶体成功实现了场效应器件工作并测出其空穴载流子迁移率；通过气相沉积方法生长的TPA-PE片状晶体表明质量更高，场效应器件的空穴迁移率可以达到0.02-0.1cm~2V~(-1)s~(-1)，且器件表现出非常好的稳定性；AFM测试表明气相沉积得到的TPA-PE晶体表面依然不够平整，故迁移率还有可能更高；总体来说扭曲结构D-A分子在高载流子迁移率上有着较大的潜力和研究空间。
The organic light-emitting diodes (OLEDs) as one of the most importantapplications of organic luminescent molecules have been widely studied. In the pastdecades, the rapid development of OLEDs benefited mainly from the emergency oflayered nanoscale-thickness-film device structure and the application of highlyefficient phosphorescent materials. Nowadays, OLEDs have come to the stage ofapplication in industry production, but the cost of rare and expensive heavy metal inphosphorescent materials prevents it for further development in the future.
The performance of OLEDs is ultimately decided by the theoretically attainableradiative excitons ratio for electroluminescence. In phosphorescent device the75%triplet excitions formed in electric condition by spin coupling statistics could beeffectively employed, in many cases, the proportion was nearly100%. If a pureorganic material can fully employ100%excitons like a metal-based phosphorescentmaterial, it is very significant for the development of OLEDs due to their advantage incost and resource. In current stage, some investigations based on delayed fluorescenceby transferring triplet excitons to singlet for employing more than25%excitonsthrough TTA or TADF methods have been reported. In extended pi-conjugatedmolecule or polymer with delocalized electronic state, a breakthrough in the singletexciton ratio was also observed, which is explained by larger singlet formingprobability in weakly binding state or triplet transferring to singlet in the high energyinter-chain CT state. This directs a concept for OLED material design to breakthrough the spin coupling statistics (singlet/triplet=1/3) in strongly bound excited stateby employing molecular exciton state with weak binding energy. Thus to findfluorescent molecules with properties of weakly bound exciton in the lowest excitedstate as well as high fluorescence at the same time would be a route towards thenext-generation highly efficient OLED material design.
Charge-transfer (CT) exciton is a kind of weakly coupling interaction, in whichelectron and hole location sites are separated from and of a certain distance to eachother. The binding energy of CT exciton is supposed be a weak one in betweenWannier exciton (radius of~100, or called free electron and hole) with bindingenergy of~10meV and Frenkel exciton (radius of~10, or call local excited exciton)with binding energy of1eV. But an unavoidable problem for the CT-statephotoluminescence is just its very low quantum efficiency, arising from the forbiddenelectron transition due to the little overlap and poor symmetry of their molecularorbital. Thus to find CT state molecules with high-efficiency fluorescence is of greatimportance currently for improving the highly efficient OLED.
Twisting donor-acceptor molecule is an effective way to obtain the intramolecularCT state by breaking the conjugation between donor and acceptor to induce a CTtransition in between them. Through fixing the donor of triphenylamine andmodifying the acceptor of fluorescent molecular groups, a series of twistingdonor-acceptor molecules with high efficiency and whole-color-range emission canbe obtained. Frontier orbital and electrochemistry results show that, in the twistingdonor-acceptor molecules with twist angles of30-70degree between donor andacceptor, HOMO was localized mainly on triphenylamine and LUMO was localizedon fluorescent molecular groups, with some overlap between them, which isresponsible for the high efficiency of twisting donor-acceptor molecule. The twistconfiguration induces the hybrid of local excited state (LE) and CT state to form anew hybridized local and charge transfer (HLCT) state in the twisting donor-acceptormolecules. The bigger the twist angle is, the more the proportions of CT transitions inHLCT state are. When twist angle reach90degree, the HLCT become a pure CT statewith no light emission, that is, the hybrid of high-efficiency LE state into HLCT statemake it become a highly efficient CT state. HLCT acts as a LE state in the low polarsolvents, and a CT state in the high polar solvents. The single exponential lifetime ofHLCT state in different polar solvents confirm that it is a hybridized state, not amixture of LE and CT states. Theory calculation on the energy level of HLCT state indifferent polar solvents shows that HLCT displays a slow decrease in the low polarsolvents and a large one in the high polar solvents, which is consistent to that of solvatochromic effect of molecular spectra in the experiments. The nonlinear changeof HLCT state dipole is thought to be the root of the special solvatochromic effect oftwisting donor-acceptor molecules in different polar solvents.
OLEDs based on twisting donor-acceptor molecules with HLCT state as emitterexhibit excellent properties, especially in deep-blue, deep-red and orange colordevices, among the best reported results with similar fluorescent color. Almost all thedevices show a breakthrough in the singlet exciton ratio of more than25%(90%inthe TPA-NZP case). The decay of device emission shows nearly none delayed lightwith long lifetime. The breakthrough in the single exciton ratio in twistingdonor-acceptor molecular device is ascribe to the large singlet forming probability ofHLCT state with weak bonding energy, or the triplet transferring to singlet in thepossible inter-or intra-molecular CT state at the high energy level. Moreover, thesimultaneously stable oxidation and reduction in the twisting donor-acceptormolecules contribute much to the lifetime or stability enhancement of OLED device.
Through the solution or PVT (physical vapor transport) methods, various singlecrystal structure and molecular stack mode are discovered for twisting donor-acceptormolecules. In the case of TPA-PY, the self-assembling separately of donor andacceptor is discovered in O crystal. Field effect transistors (FETs) based on slicecrystals of TPA-PE and TPA-PY (M crystal) by solution methods show large holetransporting mobilities. FETs based on TPA-PE crystal by PVT method exhibit higherhole transporting mobilities of0.02-0.1cm~2V~(-1)s~(-1)and great device stability. Atomicforce microscopy measurements show that TPA-PE crystals display poor surfaces,indicating of possible higher mobility in TPA-PE crystal as well as the great potentialof twisting donor-acceptor molecular crystal in the FET area.
引文
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[3] FORREST S R，BRADLEY D D C，THOMPSON M E. Measuring the efficiencyof organic light-emitting devices[J].Adv.Mater,2003,15:1043-1048.
[4] TANG C W,VANSLYKE S A,et al.Organic electroluminescent diodes[J].ApplPhys Lett,1987,51:913-916
[5] SHEATS J R,ANTONIADIS H,HUESCHEN M et al.Organic electroluminescentdevices [J]. Science,1996,273:884-888.
[6] MA Y G,ZHANG H Y,CHEN C M,SHEN J C.Electroluminescence from tripletmetal-ligand charge-transfer excited state of transition metalcomplexes [J].Synth.Met.,1998,94:245-248
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[8] LAMANSKY S,DJUROVICH P,MURPHY D et al. Highly PhosphorescentBis-Cyclometalated Iridium Complexes: Synthesis, PhotophysicalCharacterization, and Use in Organic Light Emitting Diodes [J].J. Am.Chem. Soc.,2001,123:4304-4312.
[9] LIU H,CHENG G,HU D H et al. A highly Efficient, Blue-PhosphorescentDevice Based on a Wide-Bandgap Host/FIrpic: Rational Design of theCarbazole and Phosphine Oxide Moieties on Tetraphenylsilane [J].Adv.Funct. Mater.,2012,22:2830-2836.
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[14] BARFORD W, Theory of singlet exciton yield in light-emitting polymers[J]. PHYSICAL REVIEW B,2004,70:205204.
[15] SEGAL M, SINGH M, RIVOIRE K, et al. Extrafluorescentelectroluminescence in organic light-emitting devices [J]. NatureMaterials,2007,6:374-378
[16] REINEKE S, BALDO M A. Recent progress in the understanding of excitondynamics within phosphorescent OLEDs [J]. Phys. Status Solidi A209,2012,12:2341–2353.
[17] LUO Y C，AZIZ H. Correlation between triplet–triplet annihilationand electrolum inescence efficiency in doped fluorescent organiclight-emitting devices[J]. Adv.Funct.Mater.,2010,20:1285–1293.
[18] ENDO A,SATO K,YOSHIMURO,et al.Efficient up-conversion of tripletexcitons into a singlet state and its application for organic lightemitting diodes[J]. Appl.Phys.Lett.,98:083302.
[19] UOYAMA H,GOUSHI K,SHIZU K, et al.Highly efficient organiclight-emitting diodes from bdelayed fluorescence[J].Nature,2012,492:234-238.
[20] KIM S K,YANG B,MANG Y G,et al.Exceedingly efficient deep-blueelectroluminescence from new anthracenes obtained using rationalmolecular design[J].J.Mater.Chem.,2008,18:3376–3384.
[21] XIE Z Q, YANG B, LI F, et al.Cross Dipole Stacking in the Crystalof Distyrylbenzene Derivative: The Approach toward High Solid-StateLuminescence Efficiency[J].J.AM.CHEM.SOC.2005,127:14152-14153.
[22] LUO J D,XIE Z L,LAM J W Y et al. Aggregation-induced emission of1-methyl-1,2,3,4,5-pentaphenylsilole [J].Chem. Commun.,2001:1740-1741
[23] WANG J,MEI J,HU R R et al. Click Synthesis, Aggregation-InducedEmission, E/Z Isomerization, Self-Organization, and MultipleChromisms of Pure Stereoisomers of a Tetraphenylethene-CoredLuminogen [J].J. Am. Chem. Soc.,2012,134:9956-9966.
[24] XIA Y J,SUN K,OUYANG J Y.Solution-Processed Metallic ConductingPolymer Films as Transparent Electrode of Optoelectronic Devices [J].Adv. Mater.,2012,24:2436-2440.
[25] HE Z C,ZHANG C,XU X F,et al.Largely Enhanced Efficiency with a PFN/AlBilayer Cathode in High Efficiency Bulk Heterojunction PhotovoltaicCells with a Low Bandgap Polycarbazole Donor[J].Adv.Mater.,2011,23:3086–3089.
[26] ZHOU Y H,FUENTES-HERNANDEZ C,SHIM J,et al.A Universal Method toProduce Low–Work Function Electrodes for Organic Electronics[J].SCIENCE,2012,336:327-332.
[27] XUE S F,YAO L,SHEN F Z,et al.Highly Efficient and FullySolution-Processed White Electroluminescence Based on FluorescentSmall Molecules and a Polar Conjugated Polymer as theElectron-Injection Material[J].Adv.Funct.Mater.,2012,22:1092–1097.
[28] ZHAO H D,TANJUTCO C,THAYUMANAVAN S.Design and synthesis of stabletriarylamines for hole-transport applications [J].TetrahedronLetters,2001,42:4421-4424.
[29] CHU Y L, CHENG C C, YEN Y C, et al.A New Supramolecular HoleInjection/Transport Material on Conducting Polymer for Applicationin Light-Emitting Diodes[J]. Adv.Mater.,2012,24:1894-1898.
[30] SU S J,SASABE H,PU Y J,et al.Tuning Energy Levels ofElectron-Transport Materials by Nitrogen Orientation forElectrophosphorescent Devices with an‘Ideal’Operating Voltage [J].Adv.Mater.,2010,22:3311–3316.
[31] PU Y J, NAKATA G, SATOH F,et al.Optimizing the Charge Balance ofFluorescent Organic Light-Emitting Devices to Achieve High ExternalQuantum Effi ciency Beyond the Conventional Upper Limit [J]. Adv.Mater.,2012,24:1765-1770.
[32] GU C,DONG W Y,YAO L, et al. Cross-Linked Multifunctional ConjugatedPolymers Prepared by In Situ Electrochemical Deposition for aHighly-Efficient Blue-Emitting and Electron-Transport Layer[J].Adv.Mater.,2012,24:2413–2417.
[33] CHASKAR A,CHEN H F,WONG K T. Bipolar Host Materials: A ChemicalApproach for Highly Efficient Electrophosphorescent Devices [J].Adv.Mater.,2011,23:3876–3895.
[34] KIM J Y,YASUDA T,YANG Y S,ADACHI C. Bifunctional Star-Burst AmorphousMolecular Materials for OLEDs: Achieving Highly EfficientSolid-State Luminescence and Carrier Transport Induced bySpontaneous Molecular Orientation [J].Adv. Mater.,2013,DOI:10.1002/adma.201204902.
[35] CAPELLI R,TOFFANIN S,GENERALI G,et al. Organic light-emittingtransistors with an efficiency that outperforms the equivalentlight-emitting diodes[J].Nature Materials,2010,9:496-503.
[36] SATRIA Z B,TAISHI T,YOHEI Y,et al. High Mobility and LuminescentEfficiency in Organic Single-Crystal Light-Emitting Transistors [J].Adv.Funct.Mater.,2009,19:1728–1735.
[37] TAKENOBU T,BISRI S Z,TAKAHASHI T,et al.High Current Density inLight-Emitting Transistors of Organic Single Crystals [J]. PRL,2008,100:066601.
[38] NAKANOTANI H,SAITO M,NAKAMURA H,et al.Tuning of threshold voltageby interfacial carrier doping in organic single crystal ambipolarlight-emitting transistors and their bright electroluminescence [J].Appl.Phys.Lett.,2009,95:103307.
[39] WANG Y,KUMASHIRO R,NOUCHI R,et al.Influence of interfacemodifications on carrier mobilities in rubrenen single crystalambipolar field-effect transistors[J].J.Appl.Phys.,2009,105:124912.
[40] WANG Y,KUMASHIRO R,LI Z F,et al. Light emitting ambipolarfield-effect transistors of2,5-bis4-biphenylbithiophene singlecrystals with anisotropic carrier mobilities[J].Appl.Phys.Lett.,2009,95:103306.
[41] POPE M,SWENBERG C E.Electronic Processes in Organic Crystals andPolymers.Oxford University Press,1999.
[42] LEHN J M. Supramolecular Chemistry—Scope and Perspectives Molecules,Supermolecules, and Molecular Devices (Nobel Lecture)[J]. Angew.Chem. Int. Ed. Engl.,1988,27:89-112.
[43] EBERSON L. Electro Transfer Reaction in Organic Chemistry. Springer-Verlag；New York.1987.
[44] KAVARNOS G T, TURRO N J. Photosensitization by reversible electrontransfer: theories, experimental evidence, and examples [J]. Chem.Rev.,1986,86:401-449.
[45] MARCUS R A. Chemical and Electrochemical Electron-Transfer Theory[J]. Annu. Rev. Phys. Chem.,1964,15:155-196.
[46] MARCUS R A, SUTIN N. Electron transfers in chemistry and biology [J].Biochem. Biophys. Acta.,1985,811:265-322.
[47] ROTKIEWICZ K, GRELLMANN K H, GRABOWSKI Z R. Reinterpretation of theanomalous fluorescence of p-N, N-dimethylamine-benzonitrilr [J].Chem. Phys. Lett.,1973,19:315-318.
[48]SIEMIARCZUK A, GRABOWSKI Z R, KRóWCZYNSKI A, et al. Two emittingstates of excited p-(9-anthryl)-n,n-dimenthylaniline derivatives inpolar solvent [J]. Chem. Phys. Lett.,1977,51:315-320.
[49] GRABOWSKI Z R,ROTKIEWICZ K,RETTIG W,et al.Structural ChangesAccompanying Intramolecular Electron Transfer:Focus on TwistedIntramolecular Charge-Transfer States and Structures [J]. Chem. Rev.2003,103:38994031.
[50] OKADA T,UESUGI M,KOHLER G et al. Time-resolved spectroscopy of DMABNand its cage derivatives6-cyanobenzquinuclidine (CBQ) andbenzquinuclidine (BQ)[J].Chem. Phys.,1999,241:327-337.
[51] LIPPERT E, LüDER W, BOOS H. In Advances in Molecular Spectroscopy;Mangini, A., Ed.; Pergamon Press: Oxford,1962; p443.
[52] BAUMANN W,BISCHOF H,FROHLING J C et al. Considerations on the dipolemoment of molecules forming the twisted intramolecular chargetransfer state [J]. J. Photochem. Photobiol. A: Chem.,1992,64:49-72.
[53] GORSE A D, PESQUER M. Intramolecular Charge Transfer Excited StateRelaxation Processes in Para-Substituted N,N-Dimethylaniline: ATheoretical Study Including Solvent Effects [J]. J. Phys. Chem.,1995,99:4039-4049.
[54] MARGUET S,MIALOCQ J C,MILLIE P et al. Intramolecular charge transferand trans-cis isomerization of the DCM styrene dye in polar solvents.A CS INDO MRCI study [J].Chem. Phys.,1992,160:265-279.
[55] AUWERAER M V,GRABOWSKI Z R,RETTIG W, et al.Molecular Structure andTemperature-Dependent Radiative Rates in Twisted IntramolecularCharge Transfer and Exclplex Systems[J].J.Phys.Chem.,1991,95:2083-2092.
[56] DIFLEY S,BELJONNE D,VOORHIS T V. On the Singlet-Triplet Splittingof Geminate Electron-Hole Pairs in Organic Semiconductors [J].J. Am.Chem. Soc.,2008,130:3420-3427.
[57] COWAN S R,BANERJI N,LEONG W L et al. Charge Formation, Recombination,and Sweep-Out Dynamics in Organic Solar Cells [J].Adv. Funct. Mater.,2012,22:1116–1128.
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