Dicyanomethylene substituted oxocarbon dianions: A comparative computational study

A comparative and computational study of various dicyanomethylene substituted dianions of squarate (SQ1-SQ3), croconate (CR1-CR4) and rhodizonate (RH1-RH7) with absorption in the visible to the near-infrared region (300-800 nm) is reported. Rhodizonate dianions show ~100 nm red-shifted absorption as compared to corresponding croconate dianions. Similarly, croconate dianions show ~100 nm red-shifted absorption as compared to the corresponding squarate dianions. Further, on increasing the number of dicyanomethylene substitutions on the central ring, there is a change in electronic properties (absorption shifts toward longer wavelength). The drastic changes in absorption properties are due to the variation in size of the central ring as shown by DFT, TDDFT and SAC-CI data.