Highly Luminescent Chiral Carbon Nanohoops via Symmetry Breaking with a Triptycene Unit: Bright Circularly Polarized Luminescence and Size‐Dependent Properties

• Published in: Small (Weinheim an der Bergstrasse, Germany) Germany), 2024-04, Vol.20 (14), p.e2308429-n/a
• Main Authors: Guo, Shengzhu, Liu, Lin, Li, Xiaonan, Liu, Guoqin, Fan, Yanqing, He, Jing, Lian, Zhe, Yang, Huiji, Chen, Xuebo, Jiang, Hua
• Format: Article
• Language: English
• Subjects: [n]CPPs; Broken symmetry; Carbon; Circular polarization; Fluorescence; high CPL brightness; high quantum yield; Luminescence; Molecular orbitals; Optical properties; Symmetry; symmetry breaking; triptycene
• ISSN: 1613-6810; 1613-6829
• DOI: 10.1002/smll.202308429

Chiral carbon nanohoops with both high fluorescence quantum yield and large luminescence dissymmetry factor are essential to the development of circularly polarized luminescence (CPL) materials. Herein, the rational design and synthesis of a series of highly fluorescent chiral carbon nanohoops TP‐[8–13]CPPs via symmetry breaking with a chiral triptycene motif is reported. Theoretical calculations revealed that breaking the symmetry of nanohoops causes a unique size‐dependent localization in the highest occupied molecular orbitals (HOMOs) and the lowest unoccupied molecular obtitals (LUMOs) as the increasing of sizes, which is sharply different from those of [n]cycloparaphenylenes. Photophysical investigations demonstrated that TP‐[n]CPPs display size‐dependent emissions with high fluorescence quantum yields up to 92.9% for TP‐[13]CPP, which is the highest value among the reported chiral conjugated carbon nanohoops. The high fluorescence quantum yields are presumably attributed to both the unique acyclic, and radial conjugations and high radiative transition rates, which are further supported by theoretical investigations. Chiroptical studies revealed that chiral TP‐[n]CPPs exhibit bright CPL with CPL brightness up to 100.5 M−1 cm−1 for TP‐[11]CPP due to the high fluorescence quantum yield. Importantly, the investigations revealed the intrigued size‐dependent properties of TP‐[n]CPPs with regards to (chir)optical properties, which follow a nice linear relationship versus 1/n. Such a nice linear relationship is not observed in other reported conjugated nanohoops including CPPs. A series of highly fluorescent chiral carbon nanohoops TP‐[8–13]CPPs via symmetry breaking with a chiral 2, 6‐substituted triptycene motif is synthesized, which has revealed intriguing size‐dependent properties of TP‐[n]CPPs, particularly in their (chir)optical properties. Notably, the TP‐[n]CPPs display high quantum yields, leading to their exceptional brightness in circularly polarized luminescence (CPL).