日本东京大学的中村荣一（Eiichi Nakamura）小组最近成功合成了一类硼/氮掺杂的对芳基乙烯基荧光分子，该分子具有优异的荧光量子产率，有望在生物成像中得到应用。他们还使用微晶电子衍射技术确定了其分子堆积方式。 这一研究成果于2020年10月22日发表在国际顶尖学术期刊《美国化学会志》上。

研究人员通过在共轭骨架中引入硼氮杂化的五元环结构成功合成了一类硼/氮掺杂的对芳基乙烯基荧光分子。新的分子骨架结构内部的环张力使得共轭体系更为刚性、平坦，而硼原子和氮原子之间的配价键也比碳-碳键更容易形成，使得合成设计大为简化。硼-氮配价键还大大降低了最高已占分子轨道（HOMO）和最低未占空轨道（LUMO）之间的带隙，从而导致该分子与全碳五元环的结构类似的分子相比，在发射光谱和吸收光谱上都出现了明显的红移，但该分子保留了在溶液和薄膜中的高光稳定性和高荧光量子产率。

具有两个硼氮杂化五元环的化合物最大发射峰为540 nm而斯托克斯位移仅有20 nm，其荧光量子产率为98％。该分子还是一种优秀的可用于活细胞成像的亲脂性荧光染料，在实验中显示出比商品化的BODIPY基荧光染料更高的光稳定性。

据介绍，线性共轭系统长期以来是许多共轭材料的设计模板，但其性能被两个内在的结构问题所困扰，即分子间作用力导致的潜在的不稳定性，以及连接碳碳双键的碳碳单键旋转导致结构缺乏刚性。解决以上问题的尝试包括在共轭系统中插入芳香性单元或引入碳桥，以阻碍碳碳单键的旋转。

附：英文原文

Title: B/N-Doped p-Arylenevinylene Chromophores: Synthesis, Properties, and Microcrystal Electron Crystallographic Study

Author: Hua Lu, Takayuki Nakamuro, Keitaro Yamashita, Haruaki Yanagisawa, Osamu Nureki, Masahide Kikkawa, Han Gao, Jiangwei Tian, Rui Shang, Eiichi Nakamura

Issue&Volume: October 22, 2020

Abstract: Linearly conjugated systems have long served as an archetype of conjugated materials, but suffer from two intrinsic structural problems: potential instability due to intermolecular interactions and the flexibility of the C–C bonds connecting C═C bonds. Efforts to solve these problems have included the insertion of aromatic units as a part of the conjugation and the introduction of carbon bridges to stop the bond rotation. We report here B/N-doped p-arylenevinylene chromophores synthesized through the incorporation of a cyclopenta[c][1,2]azaborole framework as a part of the conjugated system. The ring strain intrinsic to this new skeleton both flattens and rigidifies the conjugation, and the B––N+ dative bond is much easier to form than a C–C bond, which simplifies the synthetic design. The B–N dative bond also reduces the HOMO–LUMO gap, thereby causing a significant redshift of the absorption and emission compared with their all-carbon congeners while retaining high photostability and high fluorescence quantum yield in both solution and film states. A doubly B/N-doped compound showed emission peaks at 540 nm with a small Stokes shift of 20 nm and a fluorescence quantum yield of 98%. The molecules serve as excellent lipophilic fluorescent dyes for live-cell imaging, showing a higher photostability than that of commercially available BODIPY-based dyes.

DOI: 10.1021/jacs.0c10337

Source: https://pubs.acs.org/doi/10.1021/jacs.0c10337