Fig. 2

Optical spectra. The 77 K phosphorescence a and 298 K fluorescence b of cycLa-phLa (λ_exc = 273 nm) in the solid state. c Room temperature absorption spectrum of cycLa-phEu in buffer solution at pH 7.4 at two concentrations: black, 5 μM; red, 10 μM. The insert d shows the simulated absorption spectrum in the gas phase between 300 and 700 nm as determined from LUMPAC³⁰ with the triplet levels calculated to low energy of 316 nm marked by vertical lines. The singlet transitions were broadened with widths of 2000 cm⁻¹