具有非线性光学响应的碳硼烷衍生物设计与合成

Nonlinear optics are being widely used in our social life, and for sake of continuation of this thriving perspective, the pursuing of new NLO materials is thus becoming crucial. As remarkable members of NLO motif, the organic or organometallic nonlinear compounds have been the subject of intense investigation in the last two decades. Compared to the inorganic NLO counterparts, they possess higher non-linear coefficient, faster response, higher damage threshold, more facility for modification, and for organometallic ones, additional MLCT (metal to ligand charge transfer) which significantly improves NLO performances. The basic principle for constructing organic NLO molecules is to connect the electron donor and acceptor with ∏ bridge, which is in general based on aryl or aromatic heterocyclic groups. However, the rigid explorations with aryl systems have brought about considerable limitations such as less diversity, less flexibility, for the findings of more advanced materials. In this funding proposal, we present the designing of NLO molecules which are based on ortho-carobrane. 0-Carborane (C2B10H12) is a polyhedral boron-carbon molecular cluster that stabilized by electron-delocalized covalent bonding in the skeletal framework. Several remarkable features within 0-carorane are the three-dimensional cluster aromaticity, the electron deficiency at carbon sites and the electron sufficiency at boron sites, all of which indicating carborane as a possible alternative of aryl. Carborane derivatives as organic emitting examples have been also reviewed, and the predominant emissive behaviors within them are originated from the photo-induced electron transfer, in good agreements with the requirements of non-linear optics. Based on the well-known organic non-linear systems, we are trying to building possible NLO candidates by replacing the traditional acceptor with C-substituted carborane, the donor with B-substituted carborane, or even the ambiguous conjugator with the C,B-cosubstituted carborane. Besides, by the replacement of B(3) with Ru fragment, the organometallic carborane-based NLO derivatives can also be constructed, and due to the reverse in electron nature of carborane cage, these examples may result in even better NLO performances. Though some effort has already be contributed, this proposal aims at extending the scope of carborane derivatives with more systematic investigations and more specialization in NLO applications. With some expected results at hand, we believe this may open new avenue in both chemistry of carborane and NLO.

如今非线性正被广泛地应用于日常生活，发现新的非线性材料也变得重要。过去二十年中，(金属)有机非线性材料是研究的重点。有机类材料非线性系数高、响应速度快、损伤阈值高以及易于剪裁；金属有机类兼有金属-配体电荷转移，能够提升非线性。构建此类分子的方法是利用芳环连接电子给体和受体。然而单一的芳环体系存在着多样性、可调节性不足等限制。本项目中我们将设计碳硼烷非线性分子。碳硼烷是骨架电子离域的碳硼簇，具有芳香性、碳端缺电子性以及硼端给电子性，可成为芳环的替代者。回顾碳硼烷发光分子，主要源自光诱导电子转移，符合非线性要求。我们尝试着基于已知的有机非线性体系，通过碳硼烷碳端连接替换受体，硼端连接替代给体，或者用碳硼同时连接替代芳基构建非线性体系。另外，用钌金属替换B(3)构建金属碳硼烷，可能得到更好的性能。本项目旨在非线性领域对碳硼烷衍生物进行系统深入的研究，开拓碳硼烷和非线性光学材料的新视野。

共轭连接的D-A型有机光电材料是当前的研究热点之一。构建D-A型有机共轭分子需要同时筛选电子给体和电子受体，其中给体种类繁多，而受体的种类较少。为了发现更多优异的光电性能，寻找新的电子受体变得尤为重要。邻位碳硼烷（o-C2B10H12）是十二顶点二十面体笼状化合物，具有高热稳定性、三维芳香性、缺电子性，可以成为传统电子受体的替代者。本项目以碳硼烷为电子受体构建具有不同应用前景的D-A型功能材料。首先，我们设计了L型和V型两种分子拓扑结构，以不同数量芳基乙炔连接咔唑（D）和碳硼烷（A）。对这两个类型的碳硼烷化合物进行光物理性质研究时，我们发现L型和V型两中化合物中，CT态发光随着共轭增长出现罕见的蓝移现象，而在L型化合物中，伴随CT发射出现的LE发射却随共轭增长红移。 理论计算显示碳硼烷激发态的27电子结构使得CT态发射产生于LUMO到比HOMO更低能级的跃迁，形成蓝移。其次，我们设计了苯环连接双碳硼烷为电子受体，并以此构建大共轭D-A-A-D结构。我们初步测定了其基态吸收光谱，发现双碳硼烷体系较单碳硼烷体系在摩尔吸收系数上有了明显的提升。再次，我们意外发现了一系列芴基碳硼烷，呈现出高达95% 量子效率晶体发光。晶体结构分析显示，芴基碳硼烷分子间以H…π相互作用，在碳硼烷C-C键延伸方向实现紧密堆积，能够有效阻止基团振动导致的淬灭效应。最后，我们将电子给体引入芴基碳硼烷体系，得到了一系列具有优异固体发光的碳硼烷化合物。当电子给体为苯基咔唑时，晶体的发光效率85%，且激发态寿命达到0.83 μs。当电子给体为异构的苯基咔唑时，晶体发光效率高达95%，但激发态寿命仅为6.88 ns。我们发现造成激发态寿命巨大差异的原因是π…π 堆积的存在，而当分子间只以H…π相互作用实现紧密堆积时，能够实现高效率长激发态寿命的固体荧光发射。本项目的研究表明了碳硼烷在非线性光学和电致发光领域均具有很好的应用前景，值得进一步探索。