Tetraphenylhexaazaanthracenes: 16π Weakly Antiaromatic Species with Singlet Ground States

Org Lett. 2015 Aug 21;17(16):4026-9. doi: 10.1021/acs.orglett.5b01923. Epub 2015 Aug 5.

Abstract

Tetraphenylhexaazaanthracene, TPHA-1, is a fluorescent zwitterionic biscyanine with a closed-shell singlet ground state. TPHA-1 overcomes its weak 16π antiaromaticity by partitioning its π system into 6π positive and 10π negative cyanines. The synthesis of TPHA-1 is low yielding and accompanied by two analogous TPHA isomers: the deep red, non-charge-separated, quinoidal TPHA-2, and the deep green TPHA-3 that partitions into two equal but oppositely charged 8π cyanines. The three TPHA isomers are compared.