Synthesis and electronic properties of alkynylated phenothiazines

Alkynylated phenothiazines 1, 2, 5, 7, and 12-15 can be synthesized in moderate to excellent yields by sequences of aldehyde-alkyne transformations and/or Sonogashira cross-coupling reactions from suitable phenothiazine aldehydes or bromides. The electronic properties of (hetero)aryl ethynyl-substituted N-methyl-phenothiazines (UV/Vis absorption, fluorescence, redox potentials) strongly correlate with Hammett sigma(P) parameters and indicate that remote substituents transmit their electronic information through pi-electron delocalization and the sigma-framework. Phenothiazinyl dyads (7g, 12, 13) and triads (14) reveal different degrees of intramolecular electronic coupling as demonstrated by cyclic voltammetry, qualifying them as good model candidates for redox-active molecular wires. (C) Wiley-VCH Verlag GmbH Co.