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

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 φΔ = 0.72 for 2, relative to that for rose bengal (RB) in methanol as reference (φΔ = 0.8).