Cw/pulsed ESR study of bis[dianthrylcarbene] coupled by 1,4-diethynylbenzene

Cw and pulsed ESR spectroscopy have been applied to bis[dianthrylcarbene] coupled by 1,4-diethynylbenzene in order to investigate electronic and molecular structures of the biscarbene. Spin multiplicity of the biscarbene was identified by 2D-Electron Spin Transient Nutation (2D-ESTN) spectroscopy. 2D-ESTN spectra showed that the biscarbene has a thermally accessible excited triplet state. It is concluded that the two dianthrylcarbene units are antiferromagnetically coupled through 1,4-diethynylbenzene. A fine-structure parameter D of the triplet state determined by the spectral simulation was fairly large compared with that expected from a distance between the two localized non-bonding electron spins on the divalent carbons, indicating an unusually large delocalization effect of the π-electron spin from the carbene sites to a 1,4-ethynylbenzene unit and dianthryl moieties. A large amount of the delocalization arises from the perpendicular conformation of the n-conjugations at the divalent carbon sites.