Synthesis, Properties, and Polymerization of Spiro[(dipyridinogermole)(dithienogermole)]

Compounds
with spiro-condensed dithienogermole (DTG) and dipyridinogermole
(DPyG) units were synthesized, and their optical and electrochemical
properties were investigated. The reaction of tetrachlorogermane and
3,3′-dilithio-5,5′-bis­(trimethylsilyl)­bithiophene, followed
by treatment of the resulting mixture containing 1,1-dichlorodithienogermole
with 3,3′-dilithio-4,4′-bipyridyl, gave spiro­{(dipyridinogermole)
[bis­(trimethylsilyl)­dithienogermole]} (sDPyDTG1). The
UV–vis spectrum of sDPyDTG1 showed absorption
bands that were due to both electronically isolated DTG and DPyG units.
In contrast, the photoluminescence (PL) spectrum showed only the band
ascribed to the DTG unit even when the DPyG unit was irradiated, indicating
intramolecular photoenergy transfer. It was also suggested that photoinduced
electron transfer from DTG to DPyG occurred to suppress the PL quantum
yield. Bromination of sDPyDTG1 with NBS provided the
dibromide, and the subsequent Stille coupling of the resulting dibromide
with distannylbithiophenes produced the corresponding conjugated oligomer
and polymer. The oligomer and the polymer also showed different optical
properties, suggesting intramolecular photoenergy and electron transfer,
depending on the substituent.