Synthesis of a borylated boron–dibenzopyrromethene dye enabling the visual detection of H₂O₂ vapor

Given our interest in the development of reaction-based chemosensors, we developed a novel boron–dibenzopyrromethene dye with a pinacolboryl group (1), blue in color (λ_max = 621 nm, ε = 8.74 × 10⁴ M⁻¹ cm⁻¹) with red emission (λ_max = 643 nm, λ_ex = 550 nm) in THF. H₂O₂-mediated oxidation of the pinacolboryl group was found to induce a significant fluorescence decrease at 642 nm (λ_ex = 550 nm) in EtOH/H₂O (1 : 1 v/v) at 25 °C, enabling us to detect trace levels of H₂O₂ visually. The time-dependent response was investigated to evaluate the pseudo-first-order rate constant of 1.69 min⁻¹ under basic conditions, meaning that its fluorescence was decreased by 80% in 2 min. Such a remarkable response capability motivated us to test the suitability of 1 for the detection of H₂O₂ vapor. For these experiments, a 1-coated TLC plate was fabricated by a spin-coating method and then placed in sealed bottles with H₂O₂ vapor. It was found that the increasing vapor concentration of H₂O₂ could be visually monitored by a change in red emission (ΔR value). Based on this, we estimated the detection limit of this method to be 8.43 ppb. We also found that the 1-coated TLC plate could selectively detect H₂O₂ vapor over common solvents tested.