4 years ago

Unsymmetrical and Symmetrical Push–Pull Phenothiazines

Unsymmetrical and Symmetrical Push–Pull Phenothiazines
Prabhat Gautam, Rajneesh Misra, Yogajivan Rout
A series of unsymmetrical and symmetrical push–pull phenothiazines (37) were designed and synthesized by the Pd-catalyzed Sonogashira cross-coupling reaction and subsequent [2 + 2] cycloaddition–retroelectrocyclization reaction with tetracyanoethylene (TCNE) and 7,7,8,8-tetracyanoquinodimethane (TCNQ). The effect of systematic variation of the number and nature of cyano-based acceptor TCNE and TCNQ units on the photophysical, electrochemical, and computational studies was investigated. The single-photon absorption on phenothiazines 37 reveals that substitution of 1,1,4,4-tetracyanobutadiene (TCBD) and a cyclohexa-2,5-diene-1,4-diylidene-expanded TCBD unit results in strong intramolecular charge transfer and lowering of the LUMO energy level. The TCBD-linked and cyclohexa-2,5-diene-1,4-diylidene-expanded TCBD-linked phenothiazines 37 exhibit multiredox waves. The computational studies on phenothiazines 37 exhibit substantial stabilization of the LUMO with the increase in acceptor strength, which results in lowering of the HOMO–LUMO gap.

Publisher URL: http://dx.doi.org/10.1021/acs.joc.7b00991

DOI: 10.1021/acs.joc.7b00991

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