New strong organic acceptors by cycloaddition of TCNE and TCNQ to donor-substituted cyanoalkynes

Donor-substituted 1,1,2,4,4-pentacyanobuta-1,3-dienes and a cyclohexa-2,5-diene-1,4-diylidene-expanded derivative were prepared by a [2 + 2] cycloaddition of tetracyanoethene (TCNE) or 7,7,8,8-tetracyanoquinodimethane (TCNQ) to anilino-substituted cyanoalkynes, followed by retro-electrocyclisation; they feature intense bathochromically-shifted intramolecular chargetransfer bands and undergo their first one-electron reductions at potentials similar to those reported for TCNE and TCNQ.