B,N-Embedded Double Hetero[7]helicenes with Strong Chiroptical Responses in the Visible Light Region

Abstract

The development of helicene molecules with significant chiroptical responses covering a broad range of the visible spectrum is highly desirable for chiral optoelectronic applications; however, their absorption dissymmetry factors (g abs ) have been mostly lower than 0.01. In this work, we report unprecedented B,N-embedded double hetero[7]helicenes with nonbonded B and N atoms, which exhibit excellent chiroptical properties, such as strong chiroptical activities from 300 to 700 nm, record high g abs up to 0.033 in the visible spectral range, and tunable circularly polarized luminescence (CPL) from red to near-infrared regions (600−800 nm) with high photoluminescence quantum yields (PLQYs) up to 100%. As revealed by theoretical analyses, the high g abs values are related to the separate molecular orbital distributions owing to the incorporation of nonbonded B and N atoms. The new type of B,N-embedded double heterohelicenes opens up an appealing avenue to the future exploitation of high-performance chiroptical materials.

An S-shaped double helicene showing both multi-resonance thermally activated delayed fluorescence and circularly polarized luminescence

“…There are only two reports where the MR-TADF core structure shows intrinsic chirality and both are boron/nitrogen-based helicenes: compounds BN5 86 and OBN-Cz (aka 1a ). 87…”

Azulene‐Embedded [n]Helicenes (n=5, 6 and 7)

“…Due to the non‐mirror frontier orbitals of azulene, the distribution of lower energy orbitals and higher energy orbital (HOMO−1/HOMO−2 and LUMO+1 for [6]AzH , and HOMO−1/HOMO−3 and LUMO+1 for [7]AzH ) are largely separated (Figure S16), which are ascribed to the transitions of S 0 to S 2 according to TD‐DFT calculations (Tables S7 and S8). Thus, the separated molecular orbitals might account for the high |g abs | values of azulene‐embedded helicenes [4j] …”

The Rise of 1,4‐BN‐Heteroarenes: Synthesis, Properties, and Applications

“…Notably, at the same time, Wang and co‐workers independently reported compounds 69a,b as well as compound 69c , and disclosed their excellent chiroptical properties as a new type of B,N‐embedded double hetero[7]helicenes, such as high absorption dissymmetry factors ( g abs ) and efficient circularly polarized luminescence (see Section 3.2 ). [ 31 ]…”