Electron Transfer in Self-Assembled Orthogonal Structures

Two new molecular dyads, comprising pyrromethene (bodipy) and 2,2‘:6‘,2‘ ‘-terpyridine (terpy) subunits,
have been synthesized and fully characterized. Absorption and fluorescence spectral profiles are dominated
by contributions from the bodipy unit. Zinc(II) cations bind to the vacant terpy ligand to form both 1:1 and
1:2 (cation:ligand) complexes, as evidenced by X-ray structural data, NMR and spectrophotometric titrations.
Attachment of the cations is accompanied by a substantial decrease in fluorescence from the bodipy
chromophore due to intramolecular electron transfer across the orthogonal structure. At low temperature,
nuclear tunneling occurs and the rate of electron transfer is essentially activationless. However, activated
electron transfer is seen at higher temperatures and allows calculation of the corresponding reorganization
energy and electronic coupling matrix element. In both cases, charge recombination is faster than charge
separation.