The electronic UV-Vis-NIR absorption spectra of 1-Ln were recorded as 2 mM toluene solutions (see Figure energy of these Laporte-allowed transitions into the visible region to often mask weaker Laporte-forbidden f-f transitions. This is the case for complexes containing Sm(II) ions, and as such toluene solutions of 1-Sm are deep green, with two broad and intense absorption bands spread across the visible region with λmax = 25,000 cm -1 (ε = 776 M -1 cm -1 ) and 17,182 cm -1 (ε = 355 M -1 cm -1 ). These absorptions are more intense than the feature in the UV region, which is typically assigned to charge transfer or intra-ligand absorptions. The spectrum of 1-Sm is comparable with previously reported Sm(II) complexes such as [Sm{N(SiMe3)2}2]2 (λmax = 28,600, 24,000, 18,000 and 16,200 cm -1 ) (ε = 488 M -1 cm -1 ) and λmax = 15,385 cm -1 (ε = 526 M -1 cm -1 ). By contrast, pale solutions are generally observed for Eu(II) complexes as the Laporte-allowed f-d transitions tend to occur outside the visible region, and the f-f transitions are also spin-forbidden. As such, pale yellow toluene solutions of 1-Eu are featureless apart from a band that tails into the visible region from the UV. Finally for the Yb(II) complexes no f-f transitions are possible as a result of the 4f 14 closed shell electronic structure, but the crystal field (CF) imposed can influence colors strongly by varying the energies of the f-d transitions. Toluene solutions of 1-Yb are pale yellow with a weak band tailing from the UV to the visible region, similar to 1-Eu, but this band has two distinct shoulders at λmax = 25,641 cm -1 (ε = 695 M -1 cm -1 ) and λmax = 23,256 cm -1 (ε = 356 M -1 cm -1 ). UV-Vis-NIR absorption spectroscopic data for Yb(II) phosphide complexes are scarce, but [Yb{(μ-P t Bu2)2Li(THF)}2] possesses absorption features at λmax = 45,000, 37,000, 33,300 and 27,500 cm -1 , with no bands reported at lower energies