Single oxygen generation sensitized by spiro(dipyridinogermole)(dithienogermole)s

Abstract

Three spiro(dipyridinogermole)(dithienogermole) derivatives (1–3), including newly prepared spiro(dipyridinogermole)[di(2-pyridyl)dithienogermole] (3), were examined as photosensitizers for singlet oxygen (¹O₂) generation in dichloromethane–methanol. Irradiation of their air-saturated solutions led to the generation of ¹O₂, which was readily trapped by well-known scavengers, dihydronaphthoquinone (DHN) and diphenylisobenzofuran (DPBF). Spiro(dipyridinogermole)[bis(n-hexylbithiophenyl)dithienogermole] (2) showed the best performance with a first-order rate constant that was higher than that of tetraphenylporphyrin (TPP), an efficient photosensitizer for ¹O₂ generation. This is ascribable to the efficient intersystem crossing characteristic of the dipyridinogermole unit. The quantum yield of ¹O₂ generation was φ_Δ = 0.72 for 2, relative to that for rose bengal (RB) in methanol as reference (φ_Δ = 0.8).