Azaborahelicene fluorophores derived from four-coordinate N , C -boron chelates: synthesis, photophysical and chiroptical properties.

A series of six azaborahelicenes with varying electron-donor substitution at the 4-position of the aryl residue ( i.e. , naphthyl) or with variable π-extension of the aryl residue (thianthrenyl, anthryl, pyrenyl) was prepared with an efficient and flexible synthetic protocol. These different types of functionalization afforded notably pronounced intramolecular charge-transfer (ICT) character for the dyes with the strongest electron donor substitution (NMe 2 ) or easiest to oxidize aryl residues, as evidenced by photophysical investigations. These effects also impact the corresponding chiroptical properties of the separated M - and P -enantiomers, which notably display circularly polarized luminescence (CPL) with dissymmetry factors in the order of magnitude of 10 -4 to 10 -3 . Theoretical calculations confirm the optical spectroscopy data and are in agreement with the proposed involvement of ICT processes.