Luminescent Eu(III) and Gd(III) trisbipyridine cryptates: Experimental and theoretical study of the substituent effects

Synthesis, absorption spectra and luminescence properties of a series of lanthanide trisbipyridine cryptates Ln subset of R-Bpy.R-Bpy.R-Bpy, where Ln=Eu, Gd and R=H, COOH, COOCH3, CONH-(CH2)(2)NH2 are described. Comparison of the unsubstituted parent compound with the substituted compounds shows that bipyridine substitution doesn't alter significantly the photophysical properties of the lanthanide cryptate. The absorption maximum is slightly red-shifted when three bipyridines are substituted, whereas substituting one bipyridines has a negligible effect on the absorption spectra. The experimental triplet state energy is between 21600 and 22100 cm(-1) for the series of compounds and the luminescence lifetimes at 77 K are between 0.5 and 0.8 ms in H2O and equal to 1.7 ms in DO. The experimental characterizations are completed by DFT and TD-DFT calculations to assess the ability of these approaches to predict absorption maxima, triplet state energies and structural parameters of lanthanide cryptates and to characterize the electronic structure of the excited states. The calculations on the unsubstituted parent and substituted compounds show that absorption maxima and lowest (3)pi pi* triplet state energies can be accurately determined from density functional theory (DFT) and time-dependent (TD) DFT calculations.