Intramolecular (electron) delocalization between aromatic donors and their tethered cation–radicals. Application of electrochemical and structural probes

Abstract

To study the mechanism of electronic transduction along (poly)phenylene chains, a series of aromatic donors with general formula D–B–D has been synthesized [where D = 2,5-dimethoxy-4-methylphenyl donor and B = (poly)phenylene bridge]; and the corresponding cation–radical salts D–B–D⁺˙ SbCl₆⁻ have been isolated for X-ray crystallographic analyses. The magnitude of the electronic interaction between the D and D⁺˙ moieties through the various B bridges has been measured (i) as the difference between the first and the second oxidation potentials of D–B–D donors and (ii) as the structural changes induced in neutral D by the presence of the tethered D⁺˙ group in D–B–D⁺˙ cation–radicals. The intramolecular interaction of D and D⁺˙ groups was found to occur via π-conjugation of the bridging (poly)phenylene group. As such, the electronic interaction is highly dependent on the planarity of the (poly)phenylene bridge, and can be either inhibited or promoted by the deliberate modifications of the molecular conformation. Crystal structures of compounds A, B, B⁺˙⁺˙, 1, 1⁺˙, 2, 2⁺˙, 3⁺˙, 8 and 9⁺˙ are reported.