The variety of electron-deficient sigma aromatic clusters formed by bismuth gives rise to a wide range of spectroscopic behaviors. Of particular interest are the systems capable of low-energy electronic transitions, as these have demonstrated potential as near-infrared light emitters. It is the tendency of electron-deficient bismuth to form sigma-delocalized clusters with small HOMO/LUMO gaps that gives rise to the near-infrared emissions. This property makes these species potentially valuable to the field of near-infrared optical tomography, which exploits the near-infrared window in biological tissue.