Multiple Helicenes Defected by Heteroatoms and Heptagons with Narrow Emissions and Superior Photoluminescence Quantum Yields**

Abstract

AbstractThe incorporation of heteroatoms and/or heptagons as the defects into helicenes expands the variety of chiroptical materials with novel properties. However, it is still challenging to construct novel boron‐doped heptagon‐containing helicenes with high photoluminescence quantum yields (PLQYs) and narrow full‐width‐at‐half‐maximum (FWHM) values. We report an efficient and scalable synthesis of a quadruple helicene 4Cz‐NBN with two nitrogen‐boron‐nitrogen (NBN) units and a double helicene 4Cz‐NBN‐P1 bearing two NBN‐doped heptagons, the latter could be formed via a two‐fold Scholl reaction of the former. The helicenes 4Cz‐NBN and 4Cz‐NBN‐P1 exhibit excellent PLQYs up to 99 % and 65 % with narrow FWHM of 24 nm and 22 nm, respectively. The emission wavelengths are tunable via stepwise titration experiments of 4Cz‐NBN‐P1 toward fluoride, enabling distinguished circularly polarized luminescence (CPL) from green, orange (4Cz‐NBN‐P1‐F1) to yellow (trans/cis‐4Cz‐NBN‐P1‐F2) with near‐unity PLQYs and broader circular dichroism (CD) ranges. The five structures of the aforementioned four helicenes were confirmed by single crystal X‐ray diffraction analysis. This work provides a novel design strategy for construction of non‐benzenoid multiple helicenes exhibiting narrow emissions with superior PLQYs.