Symmetry breaking and the turn-on fluorescence of small, highly strained carbon nanohoops
Symmetry breaking and the turn-on fluorescence of small, highly strained carbon nanohoops
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DOI：
10.1039/c9sc00169g
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发表时间：
2019-04-07
期刊：
影响因子：
8.4
通讯作者：
Jasti, Ramesh
中科院分区：
文献类型：
--
作者：
Lovell, Terri C.;Colwell, Curtis E.;Jasti, Ramesh
[n]环对亚苯基，或“碳纳米环”，是独特的共轭大环，具有类似于碳纳米管中的径向取向的π系统。这些分子的中心对称性质和构象刚性导致不寻常的尺寸依赖的物理特性。为了进一步研究这些效应并扩展可能的结构家族，公开了一类新的具有破缺对称性的相关碳纳米环。在这些被称为Meta[n]环对亚苯基的结构中，单个碳-碳键被移动一个位置以打破母体[n]环对亚苯基的中心对称性质。有利地，对称性破缺导致较小纳米环中的明亮发射，由于光学选择规则，这些较小纳米环通常是非荧光的。此外，这种简单的结构操作保留了nanohoop结构的最独特的特征之一-具有相对大的消光系数和量子产率的尺寸依赖性发射特性。受Tretiak及其同事早期理论工作的启发，这项联合合成，物理和理论研究提供了进一步的设计原则，以操纵这类具有径向取向π系统的分子的光学性质。
[n]Cycloparaphenylenes, or "carbon nanohoops," are unique conjugated macrocycles with radially oriented pi-systems similar to those in carbon nanotubes. The centrosymmetric nature and conformational rigidity of these molecules lead to unusual size-dependent photophysical characteristics. To investigate these effects further and expand the family of possible structures, a new class of related carbon nanohoops with broken symmetry is disclosed. In these structures, referred to as meta[n]cycloparaphenylenes, a single carbon-carbon bond is shifted by one position in order to break the centrosymmetric nature of the parent [n]cycloparaphenylenes. Advantageously, the symmetry breaking leads to bright emission in the smaller nanohoops, which are typically non-fluorescent due to optical selection rules. Moreover, this simple structural manipulation retains one of the most unique features of the nanohoop structures-size dependent emissive properties with relatively large extinction coefficients and quantum yields. Inspired by earlier theoretical work by Tretiak and co-workers, this joint synthetic, photophysical, and theoretical study provides further design principles to manipulate the optical properties of this growing class of molecules with radially oriented pi-systems.