Strong Ground and Excited State Charge Transfer in C3‐Symmetric Truxene Derived, Low‐Band Gap, Phenothiazine‐Tetracyanobutadine (TCBD) and Expanded TCBD Conjugates

C3‐symmetric, star shaped phenothiazene substituted truxene 1, synthesized by the Pd‐catalyzed Sonogashira cross‐coupling reaction, was reacted with electron acceptors tetracyanoethylene (TCNE) and 7,7,8,8‐tetracyanoquinodimethane (TCNQ) which undergo, cycloaddition‐retroelectrocyclization reaction to yield tetracyanobutadine (TCBD) and cyclohexa–2,5–diene–1,4–ylidene–expanded TCBD bearing conjugates 2 and 3. A combination of spectral, electrochemical, and photophysical investigations of 2 and 3 reveal that the functionalization of the triple bond by TCBD and expanded TCBD (abbreviated as DCNQ = dicyanoquinodimethane) has a pronounced effect on their ground and excited‐state interactions. Specifically, the existence of strong ground state interactions between phenothiazine and electron accepting TCBD or DCNQ resulting in PTZ+‐TCBD‐ or PTZ+‐DCNQ‐ charge transfer states, and subsequent ultrafast charge separation resulting in PTZ+‐TCBD‐ or PTZ+‐DCNQ‐ electron transfer products is unequalled not only in phenothiazine chemistry but also in TCBD and DCNQ‐derived donor‐acceptor conjugates. Additionally, for the first time, by manipulating spectroelectrochemical data, spectrum of the charge‐separated species is construed, and shown to be highly useful in interpreting the rather complex transient spectra.

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