【作者】 刘慧；

【导师】 沈珍；

【作者基本信息】 南京大学 ， 化学， 2020， 博士

【摘要】 电子给体-受体（D-A）构型的纯有机分子,因其显著的分子内电荷转移特征（ICT）以及独特的光电性能,在材料科学领域备受关注,是当今研究热点之一。与重金属/重原子的分子材料相比纯有机D-A分子具有易于构建、类型丰富、毒性低等优势,近年来在光电器件（如有机光伏、场效应晶体管、有机发光二极管）,生物成像,以及光催化等领域展现出广泛的应用前景。D-A分子结构的键连方式,以及供受体的类型都会对其性质产生显著的影响,因此设计、合成具有特定结构和性质的D-A分子,结合理论计算解释其构-效关系,对于理解复杂的光物理过程,并制备出具有优异光、电性质的分子材料具有深远而重要的意义。本研究论文是基于具有较强吸电子能力且结构刚性的keto-BODIPY分子,通过引入不同的给电子基团（二噻吩乙烯基团或咔唑基团）,合成了一系列新颖的D-A分子体系,实现了环境光诱导的光环化途径（Norrish-Yang vs.6π）的调控以及延迟荧光行为。主要研究成果如下:1、基于苯并噻吩/噻吩-keto BODIPY的D-A分子的合成及其光控性质研究:广泛研究的光致变色二芳基乙烯在紫外光照射下发生6π电子的光环化,而在可见光照射下则发生可逆的开环过程。虽然1,2-二酮的Norrish–Yang环化反应是由发光二极管蓝光触发的,但大多数Norrish光反应发生在紫外光汞灯照射下,会导致副反应和光损伤,特别不利于生物系统中的应用。此外,由于酮在紫外可见区的摩尔消光系数较低,它们的Norrish-Yang光环化反应总是效率低下。为了提高可见光驱动光反应的效率,我们将两个光响应基元（二芳基噻吩和酮）作为π-共轭体系的一部分并入一个生色团中,从而使n-π和π-π*的电子跃迁红移到可见光范围。由于噻吩是电子给体,酮是电子受体,这些染料的HOMO和LUMO轨道在空间上的分离促进了三重态的产生,并且在可见光区域自敏化了分子内的光环化。研究发现改变二芳基噻吩上的R取代基可以控制分子内光环化途径,当R为甲基时（如1d,2d）,发生6π的光环化,而R为乙基时（如3d,6d）则发生Norrish-Yang光环化,具有很高的光化学选择性。三维时间分辨和稳态发射光谱表明,Norrish-Yang光环化反应在毫秒内发生,转换效率高达96%,并首次通过理论计算阐明了Norrish-Yang光环化反应的机制。2、基于咔唑-keto BODIPY的D-A分子的合成及延迟发光性质研究:热致延迟荧光分子材料由于具有比较小的ΔE_ST,可以实现三重态激子反向系间窜越过程上转换到单重态,提高激子利用率,是新一代具有优异OLED发光性能的分子材料。由于keto BODIPY是一类具有刚性平面结构和较强吸电子能力的氟硼染料,通过在这类染料的异吲哚啉酮单元上引入双咔唑取代基,即形成以咔唑为电子供体,keto-BODIPY为受体的D-A分子体系。这类分子吸收光谱中存在具有精细振动结构的LE主吸收峰和长波长处强烈的CT吸收峰,基态下存在强烈的从咔唑到keto BODIPY基元的ICT效应,主吸收峰则主要源于氟硼染料母核单元。通过meso-位氮原子和氰基的取代,可将发光颜色从源于BF₂母核的蓝光调控到红光区;此外,还具有对氧气和溶剂极性都有依赖性的发光性质,即氧气和大极性溶剂都对发光强度产生淬灭效应。通过稳瞬态光谱技术以及不同温度下的时间分辨发射光谱进一步证明了延迟荧光的存在,并发现低温77 K下长达577 ms的长余辉发光寿命。结合X-射线单晶衍射,DFT理论计算考察影响延迟荧光性质的结构因素。3、基于D-A的CT发光特征的金属铱配合物:以2-二氟苯基吡啶为主配体的金属铱配合物通常具有蓝色磷光发射,然而通过改变辅助配体的共轭度可使配合物的发光红移,由源于主配体的LE蓝光发射变成了CT发光特征的红光。辅助配体结构的变化对配合物发光性质影响比较大,仅仅将吡啶基换成异喹啉基就可以使发光波长红移了近72 nm。结合X-射线单晶衍射,光谱学性质,量子化学理论计算,考察了辅助配体的电子效应以及空间构型对发光性质的影响。更多还原

【Abstract】 Pure organic molecules with electron donor-acceptor（D-A）configuration have attracted much attention in the field of materials science due to their outstanding intramolecular charge transfer（ICT）characteristics and unique photoelectric properties.With unique advantages over molecular materials based on heavy metal/heavy atoms,it has been widely used in photoelectric devices（such as organic photovoltaic,field effect transistor,organic light emitting diode）,biological imaging,and photocatalysis in recent years.In D-A molecular system,the spatially bonding mode between donor and acceptor,as well as for type of both can have a significant effect on its photophysical properties.So,the construction of D-A molecules with a certain structure,as well as exploration of structure-property relationship combined with the theoretical calculation,has profound and important significance for thorough comprehension of the complex photophysical process,and preparation of D-A molecular materials imparting with excellent optical-electrical properties.In this paper,a series of novel D-A molecular systems based on the keto-BODIPY molecule with strong electron-withdrawing ability and rigid structure were synthesized by introducing different electron-donating groups（diarylethene or carbazole moieties）.Regulation of ambient light–induced photocyclization pathway（Norrish-Yang vs.6π）and delayed fluorescence behavior were realized in this D-A system.The main research contents of this paper are as follows:1.A series of D-A molecule based on benzothiophenyl/thienyl-keto BODIPY has been prepared.The widely investigated photochromic diarylethenes undergo 6πphotocyclization upon irradiation with ultraviolet light,with the reverse process observed upon visible light irradiation.However,to the best of our knowledge,although the Norrish-Yang cyclization of 1,2-diketones was reported to be triggered by light-emitting diode blue light,most Norrish photoreactions occur under ultraviolet mercury lamp irradiation,which can lead to side reactions and photodamage,especially in biological systems.Furthermore,owing to the low molar extinction coefficient of ketones in the UV-visible region,their Norrish-Yang photocyclizations are always inefficient.To increase the efficiency of visible light–driven photoreactions,we herein incorporate two photoresponsive motifs（diarylethene and ketone）into one chromophore as part of aπ-conjugated system,thus pushing n→π*/π→π*transitions to the visible range.Thiophene is an electron donor,whereas ketone is an electron acceptor,the spatial separation of the HOMO and LUMO of these dyes promotes triplet state generation and self-photosensitizes intramolecular photocyclization in the visible light region.The results reveal that simple variation of R substituents on the diaryl moiety allows one to control the intramolecular photocyclization mechanism with high photochemical selectivity,e.g.,under ambient light,methyl-substituted 1d and 2d undergo reversible 6πphotocyclization,whereas ethyl-substituted 3d and 6d exclusively undergoes irreversible Norrish-Yang photocyclization,indicating a high photochemical selectivity.Three-dimensional time-resolved and steady-state emission spectra of 3d show that the Norrish-Yang photocyclization takes place within milliseconds with excellent conversion efficiency（96%）.And the mechanism of Norrish-Yang photocyclization was first elucidated by theoretical calculations.2.The D-A molecules based on carbazole-keto BODIPY have been synthesized.Due to relatively smallΔE_ST,thermally activated delayed fluorescence,that excited excitons undergo reverse intersystem crossing（RISC）from T₁ to S₁ generating the final emissive singlet excitons,can improve the exciton efficiency in devices.It is a new generation of molecular material with excellent OLED luminescence performance.As keto-BODIPY is a kind of BF dyes with rigid plane structure and strong electron-withdrawing ability,carbazole substituent was introduced into the isoindolinone unit of this kind of dyes,generating a D-A system with carbazole as the electron donor and keto-BODIPY as the acceptor.Absorption spectra of this molecule,show a LE main absorption peaks with fine vibration structure and an intense CT band at longer wavelength.In the ground state,there are strong ICT effects from carbazole to keto-BODIPY segment,and the LE absorption band are mainly derived from the BF₂ dye core.By meso-cyano modification,the emission color can be regulated from yellow to red.In addition,the luminescent properties are dependent on both oxygen and solvent polarity,that is,both oxygen and large polar solvent have quenching effects on luminescence intensity.The existence of delayed fluorescence was further proved by variable-temperature and time-resolved emission spectra.Furthermore,a long afterglow emission at 77 K with lifetime up to 577 ms has also been observed.The structural factors affecting the properties of delayed fluorescence were investigated by X-ray single crystal diffraction and DFT theoretical calculation.3.Iridium（Ⅲ）complexes based on 2-difluorophenylpyridine unit generally show blue phosphorescence.The luminescence behavior of this system was regulated by introducing different auxiliary ligands.The electronic effect of auxiliary ligands and the influence of space configuration on the luminescent properties were investigated by X-ray single crystal diffraction,spectroscopic property and theoretical calculation.更多还原