Potential-controlled visible and near-infrared electrochemiluminescence from a BODIPY-DO3A macrocycle conjugate

A multicolour ECL system consisting of a conjugate composed of BODIPY (boron-dipyrromethene) core coupled via an amide linkage to DOTA (1,4,7,10-Tetraazacyclododecane-1,4,7-tris(t‑butyl acetate)) was studied. When a lanthanide ion was bound to the DOTA ligand, it was found that energy transfer could be initiated by optical but not electrochemical excitation. However, ECL experiments on the conjugate in the absence of lanthanide ions, revealed an interesting dual wavelength ECL behaviour at 549 and 730 nm in both annihilation and co-reactant pathways, which could be modulated by controlling the potential. Using the 3D ECL technique to probe the potential and concentration dependence of the ECL emission, it was possible to characterise the various mechanisms giving rise to annihilation and co-reactant ECL emissions in the visible and near-infrared. Analysis of the energetics of each reaction showed that aggregation following radical ion electrogeneration explained the long wavelength emission, facilitated by the incorporation of tBu-DO3A into the BODIPY structure. This system offers interesting new insights into BODIPY-based ECL systems.