Multiphonon Relaxation in Molecular Lanthanoid Luminescence

• Applicant: Professor Dr. Michael Seitz
• Subject Area: Inorganic Molecular Chemistry - Synthesis and Characterisation
• Term: from 2014 to 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 256010690

Non-radiative deactivation of excited levels in molecular compounds by the interaction of electronic states and vibrational overtones (= multiphonon relaxation, MR) is one of the most fundamental phenomena in the photophysics of light-emitting systems. One of the most interesting class of luminophores that are severely hampered by MR via anharmonic, high-energy oscillators are molecular lanthanoid complexes that emit in the near-infrared region of the spectrum (ca. 650-2000 nm). A detailed empirical and theoretical understanding of the intricacies determining MR in these species is still in its very infancy despite of the great technological potential of near-IR luminescence in areas like biomedical imaging or optical telecommunication. The current proposal aims at alleviating this situation by developing a comprehensive understanding of MR in molecular lanthanoid luminescence. The key enabling methodology for its realization is the organic synthesis of stereochemically well defined lanthanoid complexes which are systematically labeled with heavier isotopes (e.g. C-D instead of C-H). These tailor-made, isotopologic model systems allow the quantification of critical parameters for MR induced by typical structural motifs in the ligands. In particular, the project entails the determinations of the 3D complex structures in solution (paramagnetic 1H NMR), the non-radiative deactivation rates (time-resolved luminescence spectroscopy) and the vibrational overtone properties (near-IR absorption spectroscopy) of various coupled oscillator fragments, followed by integration of all empirical data under the known theoretical framework of the inductive-resonant mechanism of non-radiative transitions. The desired groundbreaking, unified understanding of MR for high-energy, anharmonic oscillators would go far beyond the current state-of-the-art and complement the well-known energy gap law for harmonic, low-energy oscillators in all areas of molecular photophysics.

• DFG Programme: Research Grants