Tunable Low-LUMO Boron-Doped Polycyclic Aromatic Hydrocarbons by General One-Pot C–H Borylations

Boron-doping
has long been recognized as a promising LUMO energy-lowering
modification of graphene and related polycyclic aromatic hydrocarbons
(PAHs). Unfortunately, synthetic difficulties have been a significant
bottleneck for the understanding, optimization, and application of
precisely boron-doped PAHs for optoelectronic purposes. Herein, a
facile one-pot hydroboration electrophilic borylation cascade/dehydrogenation
approach from simple alkene precursors is coupled with postsynthetic
B-substitution to give access to ten ambient-stable core- and periphery-tuned
boron-doped PAHs. These include large hitherto unknown doubly boron-doped
analogues of anthanthrene and triangulene. Crystallographic, optical,
electrochemical, and computational studies were performed to clarify
the effect of boron-doped PAH shape, size, and structure on optoelectronic
properties. Our molecular tuning allowed the synthesis of molecules
exhibiting visible-range absorption, near-unity fluorescence quantum
yields, and, to our knowledge, the most facile electrochemical reductions
of any reported ambient-stable boron-doped PAHs (corresponding to
LUMO energy levels as low as fullerenes). Finally, our study describes
the first implementation of a precise three-coordinate boron-substituted
PAH as an acceptor material in organic solar cells with power conversion
efficiencies (PCEs) of up to 3%.

硼掺杂长期以来被视为石墨烯及相关多环芳烃（polycyclic aromatic hydrocarbons, PAHs）中一种极具应用前景的降低最低未占据分子轨道（Lowest Unoccupied Molecular Orbital, LUMO）能量的修饰手段。遗憾的是，合成难题始终是制约精准硼掺杂多环芳烃在光电领域开展研究、优化性能与实现应用的显著瓶颈。本研究以简单烯烃为前驱体，通过简便的一锅法硼氢化-亲电硼化级联/脱氢反应，并结合后合成硼取代修饰，成功获得了十种核与外围结构可调的环境稳定型硼掺杂多环芳烃，其中包含迄今尚未见报道的安坦蒽（anthanthrene）与三角烯（triangulene）的大尺寸双硼掺杂类似物。我们通过晶体学、光学、电化学与计算研究，阐明了硼掺杂多环芳烃的形貌、尺寸与结构对其光电性能的影响规律。通过分子结构调控，我们合成了兼具可见光吸收特性、近单位荧光量子产率的目标分子；据我们所知，这也是已报道的环境稳定型硼掺杂多环芳烃中最易发生电化学还原的体系，其最低未占据分子轨道能级可低至富勒烯水平。最后，本研究首次将精准三配位硼取代多环芳烃作为受体材料应用于有机太阳能电池，其功率转换效率（PCEs）最高可达3%。