End-to-end communication in a linear supermolecule with a BOPHY centre and N,N-dimethylanilino-based terminals

The recently introduced BOPHY (i.e., symmetrical bis(pyrrole-BF2)) chromophore is a highly attractive building block for constructing linear molecules with extended p-conjugation running along the molecular backbone. In order to assess the level of electronic communication between the terminal groups in this type of supermolecule, we have examined selective protonation and oxidation of the bis-(N,N-dimethylanilino-styryl) derivative. The amino N atoms are separated by 22.6 angstrom via a conjugated pathway but there is no indication of through-bond electronic coupling. Instead, the disparate pK(a) values and also reduction potentials found for one-electron oxidation of each aniline group are well explained in terms of very long-range electrostatic interactions. It is necessary, however, to allow for the effects of ion-pairing. As an interesting aside, it is shown that protonation can be achieved in a cast PMMA film by using a suitable photo-acid generator.