Tetraphenylhexaazaanthracene: A Case for Dominance of Cyanine Ion Stabilization Overwhelming 16π Antiaromaticity

Abstract

Tetraphenylhexaazaanthracene (I), a double-barrel cyanine dye, was synthesized. Characterization by x-ray diffraction anal. shows I to be monoclinic, P21/c. The mols. pack such that electrostatic interactions are minimized. Results of theor. calcns. support the characterization of the title compd. as a zwitterion, and establish the ground state as singlet, with the triplet being 18.9 kcal higher in energy. The emission spectrum of I is not a mirror image of the absorption spectrum, and is sensitive to concn. quenching. The emission wavelength is blue-shifted with increasing dielec. const. of the medium, indicating that the ground state is more polar than the excited state. [on SciFinder(R)]