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

• Published in: Chemistry : a European journal 2016-09, Vol.22 (39), p.13908-13915
• Main Authors: Tokoro, Yuichiro, Oishi, Anna, Fukuzawa, Shin-ichi
• Format: Article
• Language: English
• Subjects: Absorption; Absorption spectra; Acids; arenes; Aromatic compounds; Aromaticity; Catalysis; Chemical reactions; Chemistry; Crystal structure; cyclization; Data processing; Dehydrogenation; Emission analysis; Fluorescence; Fluorescence spectroscopy; fused-ring systems; luminescence; Mathematical models; Maxima; Molecular orbitals; Optical properties; Organic chemistry; Polycyclic aromatic hydrocarbons; Rhodium; Single crystals; Spectroscopic analysis; Spectroscopy; Twisting; Wavelength; X-ray diffraction
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201602474

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. Fusion and twisting: Steric hindrance for twisted polycyclic aromatic hydrocarbons (PAHs) was efficiently induced by the successive annulation and dehydrogenative cyclization of dialkynylarenes with a biphenylboronic acid. Fusion of the benzene ring toward the central ring of the PAHs induced a large degree of twisting by decreasing the aromatic character of the central ring and by the bathochromic shift of the UV/Vis absorption and emission by extended conjugation (see figure).