Synthesizing Aza[n]helicenes to the Limit: Hydrogen-bond-assisted Solubility and Benzannulation Strategy

22 November 2023, Version 1
This content is a preprint and has not undergone peer review at the time of posting.


Synthetic challenges toward anomalous structures and electronic states often involve handling problems such as insolubility in common organic solvents and oxida-tive degradation under aerobic conditions. We de-signed benzo-annulated aza[n]helicenes, which bene-fit from both the suppressed elevation of HOMO ener-gies and high solubility due to hydrogen-bonding with solvent molecules to overcome these challenges. This strategy enabled the synthesis of six new aza[n]helicenes ([n]AHs) of different lengths (n = 9–19) from acyclic precursors via one-shot oxidative fu-sion reactions. The structures of all the synthesized aza[n]helicenes were determined by X-ray diffraction (XRD) analysis, and their electrochemical potentials were measured by cyclic voltammetry. Among the syn-thesized aza[n]helicenes, [17]AH and [19]AH are the first heterohelicenes with a triple-layered helix. The noncovalent interaction (NCI) plots confirm the exist-ence of an effective π-π interaction between the layers. The absorption and fluorescence spectra red-shifted as the helical lengths increased, without any distinct satu-ration points. The optical resolutions of N-butylated [9]AH, and [11]AH were accomplished and their circu-lar dichroism (CD) and circularly polarized lumines-cence (CPL) were measured. Thus, the structural, (chir)optical, and electrochemical properties of the aza[n]helicenes were comprehensively analyzed.


circularly polarized luminescence

Supplementary materials

Supporting Information
Synthesis procedures, characterization data, details of the photophysical measurements, and NMR spectra of all new compounds


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