Experimental and theoretical study on spontaneous intermolecular charge transfer features and antiaromaticities of unusual bisazo compounds with antiaromatic cores

Abstract

Antiaromatic compounds have been applied in optoelectronic devices. In this paper, acenaphthoquinone bisphenylhydrazone (1a) and acenaphthoquinone bis(4-bromophenylhydrazone) (2a), were synthesized by a Schiff base reaction of acenaphthoquinone with phenylhydrazine or 4-bromophenylhydrazine. Two bisazo compounds with antiaromatic five-membered rings, 1,2-bisphenylazoacenaphthylene (1b) and 1,2-bis(4-bromophenylazo)acenaphthylene (2b) were respectively synthesized by oxidation reactions of compound 1a or 2a with PbO2. The crystal structures show that these compounds would be aggregated to H-aggregation structures, which were caused by the antiaromatic cores. Based on crystal structures of 1a, 2a, 1b and 2b, nucleus independent chemical shift (NICS) values were calculated. The obtained NICS (0) values for the five-membered rings located at cores of molecules 1a (3.64), 1b (4.64), 2a (4.42) and 2b (3.97) suggest that those core rings would exhibit antiaromatic nature. Crystal geometries and thermodynamic data of Gibbs free energies and entropies suggest that the bisazo compounds would easily accept and delocalize electrons in these crystals due to the antiaromatic cores and H-aggregation. This paper suggests a way of design of electron-accepting materials with spontaneous charge transfer nature.