Synthesis, Photophysical, Electrochemical, and Electrogenerated Chemiluminescence Studies. Multiple Sequential Electron Transfers in BODIPY Monomers, Dinners, Trimers, and Polymer

Synthesis of the C-8 BODIPY monomers, dimers, and trimers, a C-8 polymer, and N-8 aza-BODIPY monomer and dimer was carried out. Methyl and mesityl C-8-substituted monomers, dimers, and trimers were used. Dimers, trimers, and polymer were formed chemically through the beta-beta (2/6) positions by oxidative coupling using FeCl3. A red shift of the absorbance and fluorescence is observed with addition of monomer units from monomer to polymer for C-8 dyes. The aza-BODIPY dye shows red-shifted absorbance and fluorescence compared with the C-8 analogue. Cyclic voltammetry shows one, two, and three one-electron waves on both reduction and oxidation for the monomer, dimer, and trimer, respectively, for the C-8 BODIPYs. The separation for the reduction peaks for the C-8 dimers is 0.12 V compared with 0.22 V for the oxidation, while the trimers show separations of 0.09 V between reduction peaks and 0.13 V for oxidation peaks. The larger separations between the second and third peaks, 0.25 V for the oxidation and 0.2 V for the reduction, are consistent with a larger energy to remove or add a third electron compared with the second one. The BODIPY polymer shows the presence of many sequential one-electron waves with a small separation. These results provide evidence for significant electronic interactions between different monomer units. The aza-BODIPY dye shows a reduction peak 0.8 V more positive compared to the C-8 compound. Aza-BODIPY dimer shows the appearance of four waves in dichloromethane. The separation between two consecutive waves is around 0.12 V for reduction compared with 0.2 V for oxidation, which is comparable with the results for the C-8 dyes. Electrogenerated chemiluminescence (ECL) of the different species was obtained, including weak ECL of the polymer.