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.