2020 年 78 巻 8 号 p. 782-791
The modern history of organic electronics based on conducting polymers started with doped polyacetylene in 1970’s. However, polyacetylene suffers many problems, such as structural disorder along C-C single bonds, the resulting short effective conjugation length, and insolubility. To address these issues, many efforts were made in terms of partial rigidification of the polyene structure with heteroatom and carbon linkages. Among them, oligo(phenylenevinylene)s (OPVs) are all-carbon analogues of polyacetylenes, albeit many C-C single bonds that can freely rotate are still left in a molecular framework. We envisioned that full linkages between each phenylene and vinylene unit using sp3-carbon atoms can rigidify the entire OPV skeleton. Indeed, methylene-bridged stilbene was prepared in 1922, and the longer homologue of such carbon-bridged oligo(phenylenevinylene)s (COPV) is a framework of which construction had been a long-term challenge in a field of synthetic organic chemistry. In 2009 we have reported the synthesis of COPV based on a novel intramolecular cyclization reaction to afford a dilithiated indacene framework, a key intermediate to construct the COPV framework. Thus prepared COPV were found to show not only excellent photophysical and electronic properties due to the rigid planar π-conjugated framework, but also high stability and solubility due to the organic side chains installed on the bridging carbon atoms that sterically protect the π-conjugated framework. With these features, the COPV molecules have also served as versatile materials at a single-molecular and a bulk level, such as in organic thin-film lasers, dye-sensitized and perovskite solar cells, and molecular wires. Remarkable discoveries in the area connecting chemistry and physics include inelastic tunneling and long-range resonance tunneling at ambient temperature, which were previously observed only for organic molecules under cryogenic conditions. This class of newly prepared molecules created by the power of organic synthesis will serve as versatile materials for fundamental and applied researches in a broad range of field.