Boron complexes of cyclo[m]pyridine[n]pyrroles

Novel boron complexes were synthesized by reacting cyclo[m]pyridine[n]pyrroles (m+n= 6) with BF₃. These complexes were characterized and studied by means of NMR, UV, and fluorescence spectroscopies, and X-ray crystallography. As compared to the non-boronated starting materials, the complexes of this study are more rigid and twisted, a feature that translates into a modulation of the optical features. Specifically, these boron complexes can be either strongly fluorescent or barely fluorescent, depending on the numbers of pyridine subunits contained within the macrocycle. The present approach could thus define an attractive and potentially generalizable means for modulating the inherent optical characteristics of expanded porphyrins.