Intense Ground‐State Charge‐Transfer Interactions in Low‐Bandgap, Panchromatic Phthalocyanine–Tetracyanobuta‐1,3‐diene Conjugates

A cycloaddition–retroelectrocyclization reaction between tetracyanoethylene and two zinc phthalocyanines (ZnIIPcs) bearing one or four anilino‐substituted alkynes has been used to install a strong, electron‐accepting tetracyanobuta‐1,3‐diene (TCBD) between the electron‐rich ZnIIPc and aniline moieties. A combination of photophysical, electrochemical, and spectroelectrochemical investigations with the ZnIIPc‐TCBD‐aniline conjugates, which present panchromatic absorptions in the visible region extending all the way to the near infrared, show that the formal replacement of the triple bond by TCBD has a dramatic effect on their ground‐ and excited‐state features. In particular, the formation of extremely intense, ground‐state charge‐transfer interactions between ZnIIPc and the electron‐accepting TCBD were observed, something unprecedented not only in Pc chemistry but also in TCBD‐based porphyrinoid systems.