Electrogenerated chemiluminescence 71. Photophysical, electrochemical, and electrogenerated chemiluminescent properties of selected dipyrromethene-BF₂ dyes

The photochemistry, electrochemistry, and electrogenerated chemiluminescence (ECL) of five boron-based laser dyes (BODIPY, PM 546, PM 567, PM 580, PM 597) have been investigated. These show high fluorescence quantum yields (Φ > 0.85) for all dyes except PM 597 (Φ ≈ 0.41), because of the high degree of substitution and inductive effects of the substituents. Moderately intense ECL was observed from the three dyes, exhibiting reversible electrochemical oxidation and reduction with ECL efficiencies of ∼0.009 for PM 567, ∼0.007 for PM 580, and ∼0.003 for PM 597. The parent fluorophore, BODIPY, displayed both irreversible oxidation and reduction, because of the lack of substituents at positions 2, 6, and 8, and, hence, higher reactivity of the electrogenerated radical ions. Substituting a methyl group at position 8 stabilized the radical anion, causing a reversible reduction, as shown in PM 546. However, for both BODIPY and PM 546, irreversible chemical side reactions, such as oxidative polymerization, were responsible for the lack of ECL or low ECL efficiency.