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.