We next examined the solution state luminescence properties of 1-Eu and 1-Yb at room temperature (Table , Figures 4 and Supporting Information Figures ). Since 1-Sm possesses intense absorption bands that span the entire visible region, any emission arising from f-d or charge transfer electronic transitions are fully quenched by non-radiative decay mechanisms, hence 1-Sm is not included in this study. The luminescence of Ln(III) complexes is largely independent of the ligand field, due to the "core-like" nature of the 4f-electrons, and these processes are wellunderstood. However for Eu(II) and Yb(II), f-d excitations are possible that result in broader, shorter lived visible emission, observable since stabilization of the d-orbitals can change the relaxation pathways that are available to Ln(II) ions. In 1-Eu and 1-Yb in fluid toluene solution, excitation between 300 and 410 nm (Figure ) results in intense vibrationally broadened emission in the green (em = 555 nm) and red (em = 666 Yb, em = 475 nm). The emission bands in 1-Eu and 1-Yb are independent of excitation wavelength in both cases, confirming that the emission originates from a common excited state. The excitation spectrum recorded at the emission maxima for 1-Eu (Figure ) reveals a single, symmetric broad excitation band centered at 340 nm, with no contribution from higher energy charge transfer states. By contrast, the excitation spectrum of 1-Yb (Figure ) possesses two features at 328 and 364 nm, again with no contributions from higher energy electronic excitations. The features in 1-Eu and 1-Yb are comparable to those seen for [K(2.2.2.cryptand)][Ln{N(Si t BuMe2)2}3(THF)n] (Ln = Eu, 280 and 330 nm; Yb, 320 and 360 nm). Together, these data indicate that the emission may be a result of deactivation of an f-d excited state that is initially populated by a higher energy charge transfer state. The luminescence lifetime of 1-Eu at the emission maxima of 555 nm at room temperature was determined to be monoexponential at 1.42 s (following excitation with a 375 nm picosecond pulsed diode laser, see Supporting Information Figure ). This lifetime is slightly shorter than that recorded for [K(2.2.2.cryptand)][Eu{N(Si t BuMe2)2}3] (5.8 ±0.005 s), but is significantly longer than the luminescence lifetime observed for macrocyclic Eu(II) compounds in solution at room temperature, for example [Eu(benzo-15-crown-5)2][ClO4]2 (0.14 s in MeOH) 348). However, the lifetime of 1-Eu is much shorter than for the near-linear Eu(II) complex [Eu{N(Si i Pr3)2}2] (49.6 ±1.3 s). By contrast, the luminescence lifetime of 1-Yb could not be recorded due to it being shorter than the instrument response function (<0.5 ns), likely as a result of increased competitive non-radiative quenching processes in line with the energy gap law. Emission spectrum (Em), black trace and excitation spectrum (Ex), red trace of complex 1-Yb in toluene (0.018 mM). Excited at 300 nm (Ex), observed at 666 nm (Em).