Single and double cyclophenylene-ethynylenes (CPEs) with axial and helical chirality were synthesized by the Sonogashira cross-coupling of di- and tetraethynyl biphenyls with a U-shaped prearom. diiodoparaphenylene followed by reductive aromatization. X-ray crystallog. analyses and DFT calcns. revealed that the CPEs possess highly twisted bent structures. Bend angles on the edge of the paraphenylene units were close to the value of [5]cycloparaphenylene (CPP)-the smallest CPP to date. The double and single CPEs possessed stable chirality despite flexible biphenyl structures because of the high strain in the diethynyl-paraphenylene moiety. In both the single and double CPEs, orbital interactions along the biphenyl axis were obsd. by DFT calcns. in LUMO and LUMO+2 of the single CPE and LUMO+1 of the double CPE, which likely cause lowering of these orbital energies. Concerning chiroptical properties: boosting of the gabs value was obsd. in the biphenyl-based double CPE, as well as the binaphthyl-based single CPE, compared to the biphenyl-based single CPE. [on SciFinder(R)]
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