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Twisted Polycyclic Aromatic Systems Prepared by Annulation of Bis(arylethynyl)arenes with Biphenylboronic Acids.

Twisted polycyclic aromatic hydrocarbons (PAHs) were prepared by the successive rhodium-catalyzed annulation and dehydrogenative cyclization of bis(arylethynyl)arenes with di-tert-butylbiphenyl-2-ylboronic acid. The molecular structures of the PAHs were determined by single-crystal XRD analysis. The PAHs showed up to four fjord regions, and the twisting angle was 46.7°. The nonplanarity (NP) and harmonic oscillator model of aromaticity (HOMA) were calculated by using the structural data obtained from XRD analysis. The PAHs derived from dialkynyl naphthalenes showed low planarity and HOMA of the central ring. The optical properties of the PAHs were investigated by UV/Vis absorption and fluorescence spectroscopy analyses. The absorption and emission maxima of the PAHs with a larger planar region appeared at a longer wavelength. DFT calculations support that the absorption band at λ≈450 nm can be mainly attributed to the HOMO-LUMO transition.