Electrochemistry and Electrogenerated Chemiluminescence of n-Pentyl and Phenyl BODIPY Species: Formation of Aggregates from the Radical Ion Annihilation Reaction

The electrochemistry and the electrogenerated chemiluminescence (ECL) of the BODIPY species (2,6-diethyl-1,3,5,7-tetramethyl-8-n-pentyl-4,4-difluoro-4-bora-3a,4a-diaza-s-indacene, i.e., B-8-n-pentyl), an aromatic monomer (B-8-phenyl), and a closely related dimer were examined. The B-8-n-pentyl species with the n-pentyl donor chain in the meso position shows good electrochemical behavior in MeCN with the formation of stable radical ions. The ECL emission is characterized by long-wavelength emission during consecutive oxidation and reduction steps. This is attributed to aggregate formation on radical ion annihilation, the extent of which increased with increasing concentration of the compound. The B-8-phenyl electrochemistry also shows stable radical ions. However, B-8-phenyl with the meso phenyl group ECL emission does not show any long-wavelength emission. The synthesized dimer closely related to this species shows two electrochemical oxidations with peak separations of 0.5 V and two reductions with peak separations 0.2 V, which corresponds to a high degree of intermolecular interactions in the molecule. The growth of additional electrochemical peaks during the oxidation and reduction of B-8-n-pentyl was not seen, and both radical ions were stable, suggesting that emitting secondary products were not formed.