Estimation of Singlet Oxygen Quantum Yield Using Novel Green-Absorbing Baird-type Aromatic Photosensitizers

We report two new organic green-absorbing singlet oxygen (¹ O₂ ) photosensitizers: Quinoidal naphthyl thioamide (QDM) and bis-iodol-dipyrrolonaphthyridine-dione (I₂ -DPND), with triplet energies of 40.8 and 47.5 kcal mol^-1 (at 77 K in a glassy matrix) , respectively. The UV-vis absorption and emission characteristics of QDM and I₂ -DPND are similar to other commercially available organic ¹ O₂ photosensitizers such as Rose Bengal, which was used as standard/reference to estimate the ¹ O₂ quantum yield (Φ_∆ ) of the chromophores under study. Using 9,10-diphenylanthracene (DPA) as an ¹ O₂ quencher, we estimated the Φ_∆ ≈ 67-85% for QDM and Φ_∆ ≈ 25-32% for I₂ -DPND. The discrepancy in the Φ_∆ values could be explained by the apparent photo-decomposition of the later dye. Nevertheless, the high Φ_∆ value for QDM is unprecedented, as this chromophore exhibits relatively low structural complexity and could further be derivatized to create novel photodynamic agents.