Tuning the Donor−π–Acceptor Character of Arylborane–Arylamine Macrocycles

Donor−π–acceptor
compounds based on arylamine
and arylborane moieties connected by a π-conjugated linker are
attractive materials in organic electronics and imaging applications
due to the strong charge transfer character that leads to low energy
absorption and solvatochromic emission properties. Here we introduce
a new conjugated macrocyclic system that consists of four arylborane
and two arylamine units as confirmed by single-crystal X-ray structure
analysis. The acceptor character of the arylboranes is enhanced by
exocyclic electron-withdrawing 2,4,6-tris­(trifluoromethyl)­phenyl (FMes) substituent as well as the mutual interaction between
adjacent boranes. The absorption, solvent-dependent emission, and
electrochemical properties are studied and compared to those of other
macrocyclic organoboranes. Computational studies offer additional
insights into the electronic structure. Due to the enhanced acceptor
character of the boranes, the LUMO orbitals are lower lying, leading
to more facile reduction, red-shifted absorption and emission, and
larger Stokes shifts than those found for previously studied B–N
macrocycles.