Expanding the Chemical Structure Space of Opto-Electronic Molecular Materials: Unprecedented Push–Pull Chromophores by Reaction of a Donor-Substituted Tetracyanofulvene with Electron-Rich Alkynes

The reaction of a 3,5-bis­(<i>N</i>,<i>N</i>-dimethylanilino)-substituted 2,4,6,6-tetracyanopentafulvene (TCPF) with mono- and bis­(<i>N</i>,<i>N</i>-dimethylanilino)­acetylene provides facile access to push–pull chromophores with diverse new scaffolds. The starting TCPF reacts with bis­(<i>N</i>,<i>N</i>-dimethylanilino)­acetylene in a formal [2+2] cycloaddition at the exocyclic double bond, followed by retroelectrocyclization, to yield an ethenylene-extended push–pull pentafulvene. The transformation with 4-ethynyl-<i>N</i>,<i>N</i>-dimethylaniline also yields a similar extended pentafulvene as well as two other products that required X-ray analysis for their structure elucidation. One features an 8,8-dicyanoheptafulvene core formed by formal [2+2] cycloaddition, followed by ring opening via fragmentation. The second is a chiral cyclobutenylated tetrahydropentalene, resulting from a cascade of formal [6+2] and [2+2] cycloadditions. All new nonplanar push–pull chromophores display amphoteric redox behavior with both strong electron-donating and -accepting potency. Notably, the <i>N</i>,<i>N</i>-dimethylanilino-substituted extended pentafulvenes show remarkably low oxidation potentials (0.27/0.28 V vs Fc/Fc<sup>+</sup> reference) that are lower than those for <i>N</i>,<i>N</i>-dimethylaniline itself. The push–pull-substituted extended pentafulvenes feature intense electronic absorption bands, extending over the entire visible spectral range into the near infrared, and low highest occupied molecular orbital–lowest unoccupied molecular orbital gaps. These properties, together with high thermal stability and good solubility, suggest the potential use of the new chromophores as advanced materials in molecular electronics devices.