Characterization of Nonanuclear Europium and Gadolinium Complexes by Gas-Phase Luminescence Spectroscopy

Gas-phase measurements using mass-spectrometric techniques allow determination of the luminescence properties of selected molecular systems with knowledge of their exact composition. Furthermore, isolated luminophores are unaffected by matrix effects like solvent interactions or crystal packing. As a result, the system complexity is reduced relative to the condensed phase and a direct comparison with theory is facilitated. Herein, we report the intrinsic luminescence properties of nonanuclear europium­(III) and gadolinium­(III) 9-hydroxyphenalen-1-one (HPLN)–hydroxo complexes. Luminescence spectra of [Eu₉(PLN)₁₆(OH)₁₀]⁺ ions reveal an europium-centered emission dominated by a 4-fold split Eu­(III) hypersensitive transition. The corresponding Gd­(III) complex, [Gd₉(PLN)₁₆(OH)₁₀]⁺, shows a broad emission from a ligand based triplet state with an onset of about 1000 wavenumbers in excess of the europium emission. As supported by photoluminescence lifetime measurements for both complexes, we deduce an efficient europium sensitization via PLN-based triplet states. The luminescence spectra of the complexes are discussed in terms of a square antiprismatic europium/gadolinium core structure as suggested by density functional computations