Naphthalene diimides (NDI) are planar electron acceptors that have been studied for applications in organic electronics, pigments and biological applications. Here we show that sulfur substitution of the carbonyls of a core-substituted napthalene diimide (RF2) results in a controlled red-shift of the absorption. The UV-visible absorption spectra exhibit a 50 nm shift for each sulfur substitution: 630, 680, 730 nm for RF2, RF2-1S and RF2-2S, respectively. Cyclic voltammetry showed lower reduction potentials (-1.39, -1.17 and -1.03 V vs Fc/Fc+) and decreasing HOMO-LUMO gaps (2.00, 1.83 and 1.71 eV) for RF2, RF2-1S and RF2-2S, respectively. Thionation of the carbonyls is a promising tool to develop new materials that combine high electron affinity and absorption in the near IR.