Chemical and Electrochemical Dimerization of BODIPY Compounds: Electrogenerated Chemiluminescent Detection of Dimer Formation

The electrochemistry of several difluoroboradiaza-s-indacene (BODIPY) compounds lacking substituent groups in the meso (8)- and/or 3 (alpha)-positions was investigated. Chemical and electrochemical dimerization was demonstrated, and the dirnerization depended on the character of substitution. The chemical dimerization was achieved by oxidative coupling using FeCl3 in CH2Cl2 at 0 degrees C. The electrochemical dimerization proceeded via anodic oxidation to the radical cation and monitored by both cyclic voltammetry (CV) and electrogenerated chemiluminescence (ECL). An available open 3-position was important for the formation of the dimer. The resulting 3,3'-dimer produced a second peak in the CV oxidation and also the appearance of a longer wavelength ECL peak at 656 nm, which is considerably shifted from the parent peak at 532 nm. No dimerization was seen for BODIPY molecules in which only the meso 8-position was unsubstituted, either by chemical or electrochemical means, demonstrating that dimerization occurs at position 3.