We present rational design of phenothiazine dyes by controlled quinoidization of the thiophene unit. We systematically study the effect of electron-withdrawing functional groups including pseudo- and superhalogens. We propose a new dye where a fumaronitrile unit induces an increase in the bond length alternation and a concurrent red shift in the absorption spectrum vs. the parent dye. The visible absorption peak is predicted at 520 nm, in CH2Cl2 vs. 450 nm for the parent dye. The LUMO and HOMO levels of the new dye are suitable for injection into TiO2 and regeneration by available redox shuttles, respectively. (C) 2014 Elsevier B.V. All rights reserved.