【作者】 王涛；

【导师】 张兴元； 张国庆；

【作者基本信息】 中国科学技术大学 ， 高分子化学与物理， 2019， 博士

【摘要】 近年来纯有机发光材料受到了世界各地研究人员的广泛关注,尤其是热活化延迟荧光和室温磷光材料。这类材料在传感器、光电器件、生物成像以及数据加密等领域存在着巨大的应用前景。现阶段来说,设计热活化荧光和室温磷光的关键在于提高反系间窜越和系间窜越的效率。如今比较流行的方法主要有两种:(1)利用分子内或分子间电荷转移态作为单线态和三线态的媒介来促进单线态激子和三线态激子的交流;(2)设计HOMO能级和LUMO能级空间分离的分子结构以实现较小的单线态和三线态能级差。通常,发光分子会被制备成晶体或分散在高分子基质中以避免聚集诱导淬灭效应。本博士论文主要的研究分为两部分:(1)聚集诱导发光型热活化延迟荧光和室温磷光材料设计开发;(2)高分子基质分散的室温磷光材料的设计开发。具体内容如下:1.基于咔唑给体和氰基苯受体合成了一系列聚集诱导热活化延迟荧光的给体-受体二联体结构。这类分子在有机良溶剂中,由于光诱导电荷转移作用,使得氰基苯能够淬灭咔唑基元的激子。当其形成聚集态后,咔唑和氰基苯之间形成的电荷转移态能够作为单线态和三线态之间沟通的媒介以促进激子的系间窜越和反系间窜越,从而实现热活化延迟荧光。值得注意的是,这类分子在水和四氢呋喃的混合溶液中能够自组装成长达数厘米的宏观纤维,其绝对量子产率最高可达39%。最后,将所制备的聚集诱导热活化延迟荧光分子作为有机发光二极管的发光层来研究其电致发光性能。2.基于联咔唑和二苯甲酮以及二苯基砜合成了四种化学共轭连接的二联体结构,这类二联体结构具有明显的聚集诱导室温磷光特征。在溶液状态下,由于分子内旋转以及扭曲的电荷转移态作用淬灭激子,这类二联体几乎不发光。然而,当其形成聚集态结构时,分子内旋转以及扭曲的电荷转移态作用被限制,使得激子可以从激发态以辐射跃迁的方式回到基态。值得注意的是,联咔唑-二苯甲酮类二联体表现出明显的双重室温磷光特征,其发光绝对量子产率最高达64%。实验计算和理论计算的一致性进一步证明这类聚集诱导发光的二联体分子具有高效的双重室温磷光发射。为了表明这类分子在光电领域具有巨大的应用前景,我们将这类分子作为发光层制备成成非掺杂的机发光二极管。实验结构表明,所制备的有机发光二极管的外转换效率最高达5.8%,超过了传统荧光型有机发光二极管的效率极限(～5%)。3.通过改变电子受体种类,设计了三种给体-受体型分子。此外,我们将这三种分子作为引发剂引发D,L-丙交酯开环聚合以避免发光小分子的聚集淬灭,最终得到了具有室温磷光性质的聚乳酸材料。由于聚乳酸的刚性基质效应,使得分子内运动以及分子间的碰撞得到极大程度的抑制,这三种聚乳酸分子的最高量子产率达39.4%。通过给体-受体的不同组合,从而实现了荧光发射向室温磷光发射的转变。并且,CZBP-PLA和CZAQ-PLA表现出低温双重磷光特征。最后,我们将三种发光聚乳酸材料制备成纳米粒子由于细胞成像。研究结果表明,磷光型CZAQ-PLA的成像的信噪比明显优于荧光型的CZNI-PLA。4.基于萘酰亚胺类二醇合成了一系列单组分的荧光/室温磷光双发射的水性聚氨酯材料。通过将小分子染料以化学共价键的形式接入到高分子主链中来抑制热振动引起的激子淬灭。此外,基于重原子效应促进自旋轨道耦合原理,在萘酰亚胺分子上引入溴原子来增加单线态激子向三线态系间窜越的效率,最终诱导出室温磷光。对比实验结果发现,溴取代的萘酰亚胺型水性聚氨酯表现出明显的荧光/磷光双发射性质,并且RTP的强度远大于荧光强度。然而无卤原子取代的萘酰亚胺型水性聚氨酯仅仅表现出了传统的荧光发射。随着染料接入含量的增加,激发态分子和同种的基态分子形成激基缔合物导致单线态能级的降低,从而使得单线态和三线态的能级差减小,这极有可能增加单线态激子向三线态系间窜越的概率。因此,通过调控激基缔合物的形成比例的方法,有望成为设计室温磷光材料的新途径。更多还原

【Abstract】 Recently,purely organic luminescent materials,especially thermally activated delayed fluorescent（TADF）and room-temperature phosphorescent（RTP）materials,have captured worldwide researchers’ attention due to their enormously potential applications in sensors,optoelectronic devices,bioimaging,and data encryption and so on.For now,the key method for designing TADF and RTP materials is to enhance the efficiency of reverse intersystem crossing（RISC）and intersystem crossing（ISC）.Here are two common methods:（1）utilizing intra-/intermolecular charge-transfer（CT）states as a mediate bridge to promote communication between singlet and triplet excitons;（2）rationally designing molecular structure with spatially separated highest occupied molecular orbitals（HOMOs）and lowest unoccupied molecular orbitals（LUMOs）to realize small energy gap between singlet and triplet states（△EST）.Generally,luminogens are made into crystals or dispersed in polymer matrices to circumvent aggregation-caused quenching（ACQ）effect.In this thesis,the research works are mainly divided into two parts;（1）the design and development of AIE-based TADF and RTP materials;（2）the design and development of RTP materials utilizing polymers as dispersed matrices.The detailed contents are summarized as follows:1.Based on the donor,carbazole,and acceptor,cyanobenzene,a series of TADF-based donor-acceptor dyads with AIE were synthesized.In good solvents,cyanobenzene is able to quench carbazole excitons via photo-induced electron transfer（PET）effect.However,in the aggregated state,CT states formed by carbazole and cyanobenzene can serve as a bridge between singlet and triplet states,resulting in TADF generation.It is noteworthy that these dyads can self-assemble into centimeter-long macroscopic wires in THF/water mixtures,of which absolute quantum yield is up to 39%.Finally,to determine electroluminescence properties,these dyads were fabricated into organic light-emitting diode as the emitting layer.2.Based on biscarbazole,benzophenone and diphenyl sulfone derivatives,four chemically conjugated donor-acceptor dyads with distinct aggregation-induced RTP were developed.In solution,these dyads are almost non-emissive in that intramolecular motion and twisted intramolecular CT（TICT）can quench excitons while in the aggregated state,intramolecular motion and TICT are extremely restricted,leading to exciton transition to the ground state in the radiative transition mode.It is noteworthy that biscarbazole-benzophenone dyads exhibit conspicuous dual-phosphorescence with the absolute quantum yield of up to 64%.Theoretical calculations in consistency with experimental results further demonstrate these AIE dyads have high-efficiency dual-phosphorescence properties.To show a vast application foreground,these AIE molecules were fabricated into non-doped OLED as the emitting layer.As experimental results show,the maximal external quantum efficiency（EQE）of as-fabricated OLED is up to 5.8%,which surpasses that of conventional fluorescence-based OLED.3.Three types of donor-acceptor molecules were synthesized via tuning acceptor species.Besides,to avoid ACQ effect,these small molecules were used as initiators to initiate ring-opening polymerization of D,L-lactide to form RTP polylactides（PLAs）.Due to the rigid matrix effect of PLA,molecular motion and intramolecular collisions of luminogens are suppressed,which results in maximal quantum yield of 39.4%.Besides,CZBP-PLA and CZAQ-PLA have been endowed with dual-phosphorescence emission.Finally,these PLAs were prepared into nanoparticles as bioimaging agents.According to cell imaging results,the signal-to-noise ratio for phosphorescent CZAQ-PLA nanoparticle is higher than that of fluorescent CZNI-PLA nanoparticles.4.Several single-component dual-emissive waterborne polyurethanes（WPUs）with fluorescence and RTP were developed based on naphthalimide diols.By incorporating luminogens covalently into polymeric main chains,thermal vibrational relaxation can be restrained,which generally cause the quenching o excitons.Besides,given that heavy atoms can promote spin-orbit coupling,the bromine atom was introduced into naphthalimide to enhance the ISC process to produce high-efficiency RTP.By analyzing experimental results,bromine-substituted naphthalimide-based WPUs show obvious dual-emissive property with fluorescence and RTP while non-substituted naphthalimide-based WPUs only exhibit conventional fluorescence emission.With the increase in dye’s ratio in WPUs,excimers are formed,contributing to decreasing △E_ST,which is likely to promote ISC efficiency between singlet and triplet states.Therefore,tuning△E_ST via controlling the excimer ratio is a promising method to design RTP materials.更多还原