Electrogenerated Chemiluminescence of B⁸amide: A BODIPY-Based Molecule with Asymmetric ECL Transients

B 8 amide is a large molecule based on a derivative of the BODIPY laser dye PM567. Both molecules exhibit highly stable radical ions and similar absorbance and photoluminescence spectra. For B 8 amide, the redox potentials are E ° = −1.40 and 0.96 V vs SCE for reduction and oxidation, respectively, and for PM567, they are E ° = −1.37 and 0.94 V vs SCE. The absorbance and fluorescence λ max are 526 and 537 nm, respectively, for B 8 amide, and 516 and 533 nm for PM567. Whereas the ECL spectrum of PM567 consists of a single peak with λ max = 555 nm, the ECL of B 8 amide possesses peaks at 551 and 741 nm. The 741 nm peak includes a shoulder that extends to even longer wavelengths. The intensity ratio I 741 / I 551 increases as a function of pulsing time, implying that film formation contributes to the 741 nm peak. Preliminary results also suggest a lower intensity ratio for lower bulk concentrations, which usually indicates dimer, excimer, or aggregate formation; however, excimer formation for BODIPY compounds has been observed only at 650−670 nm. Phosphorescence has been observed at 770 nm, although such emission is rarely observed in solution at room temperature. The proposed film on the electrode may stabilize the triplets long enough for them to relax radiatively. The ECL transients of B 8 amide are highly stable, despite drastic alternations of intensity with each pulse. The light pulses observed on reduction are initially about 30 times smaller than those that appear on oxidation. Bulk electrolysis results indicate polymerization of the radical cation, but this is too slow to account for the dramatic intensity difference between pulses.