Optical and Photosensitizing Properties of Spiro(dipyridinogermole)(dithienogermole)s with Eletron‐Donating Amino and Electron‐Withdrawing Pyridinothiadiazole Substituents

Three spiro(dipyridinogermole)(dithienogermole) (sDPyG) derivatives with conjugated substituents on the dithienogermole system were synthesized. sDPyG with highly conjugated dithienylbenzothiadiazole substituents ( 4 ) showed moderate photoluminescence (PL) behavior with quantum yields of 15–17%, regardless of the solvent (chloroform, THF, or 1,4‐dioxane). In contrast, PL quantum yields of sDPyGs with relatively less conjugated triphenylamine and phenylcarbazole substituents, respectively ( 5 and 6 ), were decreased in polar solvents without significant solvatochromic shifts of the PL bands. This seems to indicate that the photo‐induced electron transfer took place in 5 and 6 . The sDPyGs were also examined as photosensitizers for singlet oxygen ( 1 O 2 ) generation. The first‐order rate constant for the 1 O 2 generation of 6 was k obs =0.048/min, comparable to that of tetraphenylporphyrin (TPP, 0.056/min), a typical photosensitizer for 1 O 2 generation. The quantum yield of the 4 ‐sensitized 1 O 2 generation was also determined to be 0.37.