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The introduction of unconventional elements into π-conjugated systems has been studied to manipulate the electronic states and properties of compounds. Herein, boron- and germanium-containing hybrid macrocycles, as a new class of element-hybrid conjugated systems, have been synthesized. The palladium-catalyzed Stille cross coupling of bis(bromothienyl)borane and bis(trimethylstannylthienyl)- or bis(trimethylstannylphenyl)-substituted dithienogermoles as the boron- and germanium-containing building blocks, respectively, produced a mixture of several macrocyclic compounds. Single-crystal X-ray analysis of the 2:2 coupling product revealed a planar structure with a cavity inside the macrocycle. The optical properties of the macrocyclic products indicated rather small electronic interactions between the building units. However, intramolecular photoenergy transfer from the dithienogermole unit to the boron unit was clearly observed with respect to the fluorescence spectra.

The reaction of 4,4-dichloro-2,6-di(n-butyl)dithienogermole (DTGCl) with lithium naphthalenide yielded a dark blue solution, which was treated with methyl iodide to provide a 4,4-dimethylated product in 67% isolated yield, indicating the formation of 4,4-dilithio-2,6-di(n-butyl)dithienogermole (DTGLi). Similar treatment of the dark blue solution containing DTGLi with trimethylsilyl fluoride and water gave the corresponding 4,4-disubstituted products. When trimethylsilyl chloride was used, however, no silylated products were obtained, likely due to steric hindrance. The reaction of DTGLi with DTGCl gave poly[2,6-di(n-butyl)dithienogermole-4,4-diyl], whose UV–vis absorption spectra revealed a more extended conjugation than that of a previously prepared product from the Wurtz-type coupling of DTGCl with sodium. Reinvestigation of the electronic states of poly(dithienogermole-4,4-diyl) derivatives on the basis of crystal orbital calculations was also accomplished.

Dithienosilole (DTS) and dithienogermole (DTG) are useful building units of π-conjugated organic materials. In the present work, donor-π-acceptor (D-π-A) dyes with bis(dihexyloxyphenyl)aminophenyl, DTS or DTG, and pyridine or cyanoacrylic acid as the donor (D), the π-conjugated linker (π), and the acceptor (A) units, respectively, were prepared and their optical properties were investigated. The D-π-A dyes exhibited strong absorption in the visible region, indicating efficient intramolecular donor-acceptor interaction. The addition of trifluoroacetic acid to solutions of pyridine-containing dyes led to red-shifts of the absorption bands as a result of pyridinium salt formation. Similar red-shifts were observed for cyanoacrylic acid dyes, which were due to the enhanced formation of neutral dyes relative to the separated ion pairs. The D-π-A dyes, however, showed similar absorption spectra when attached to the TiO2 surface, indicating that the dye-TiO2 electronic interaction was rather weak. In contrast to the finding that these dyes exhibited similar optical properties regardless of the π-linker (i.e., DTS or DTG), dye-sensitized solar cells (DSSCs) based on DTG-containing dyes exhibited superior performance compared to those based on DTS-containing dyes. Electrochemical impedance spectroscopy measurements supported the higher performance of the DSSCs with DTG-containing dyes.