Chemiluminescence of praseodymium (III), neodymium (III) and ytterbium (III) β-diketonates in solution excited from 1,2-dioxetane decomposition and singlet–singlet energy transfer from ketone to rare-earth β-diketonates

This work is concerned with the chemiluminescence (CL) of Nd3+, Yb3+ and Pr3+ β-diketonates in solution. Chemiluminescent reaction of adamantylideneadamantane-1,2-dioxetane (AAD) decomposition generating singlet (Ad=OS∗) and triplet (Ad=OT∗) excited adamantanone was used as a source of excited species. AAD chemiluminescence due to emission from Ad=OS∗ is quenched by Ln3+ β-diketonates: (a) by intermolecular singlet-singlet (S-S) energy transfer from Ad=OS∗ to β-diketonate ligand levels of Ln(TTA)3·2H2O and Ln(BTFA)3·2H2O; (b) by complex formation between AAD and Pr(FOD)3 or Pr(DPM)3. Corresponding Stern–Volmer quenching constants or stability constants of the complex were measured. Chemiluminescence spectra of Ln3+ β-diketonates were recorded and relative luminescence quantum yields compared. Yb3+ chelates show higher luminescence yields compared to Nd3+, due to a different efficiency of non-radiative energy degradation. Chemiexcitation of Ln3+ ions in the systems studied occurs by: (a) intermolecular singlet–singlet energy transfer: Ad=OS∗→LS∗→LT∗→Ln3+∗ (where LS∗ and LT∗ are the first singlet and triplet excited states of the β-diketonate ligand); (b) intermolecular triplet–triplet energy transfer: Ad=OT∗→LT∗→Ln3+∗; (c) intracomplex energy transfer from the decomposition of AAD in the complex with Ln3+ β-diketonate. Efficiency of chemiexcitation pathways is different for each Ln3+ β-diketonate and Ln3+ ion.