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Understanding the Quenching Effects of Aromatic C–H- and C–D-Oscillators in Near-IR Lanthanoid Luminescence

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posted on 03.10.2012, 00:00 authored by Christine Doffek, Nicola Alzakhem, Caroline Bischof, Jessica Wahsner, Tuba Güden-Silber, Joachim Lügger, Carlos Platas-Iglesias, Michael Seitz
Several series of selectively deuterated 2,2′-bipyridine-based cryptates with the near-IR emissive lanthanoids Pr, Nd, Er, and Yb are reported. The structural and luminescence properties of these complexes have been comprehensively investigated. A combination of experimental techniques (X-ray crystallography, lanthanoid-induced NMR shift analysis, luminescence, vibrational near-IR absorption) and theoretical concepts has been applied with a focus on nonradiative deactivation through multiphonon relaxation of lanthanoid excited states by aromatic, high-energy C–(H/D) oscillators. It is shown that the characteristics for the overtones of these vibrational modes deviate substantially from harmonic oscillators and that anharmonicity within a local-mode Morse model is an essential parameter for any accurate description. The spectral overlap integrals (SOIs) of lanthanoid electronic states with aromatic C–(H/D) overtones are evaluated quantitatively for different lanthanoid/oscillator combinations and the implications for luminescence enhancement through deuteration is discussed. Simple Gaussian functions are proposed as appropriate mathematical forms for the empirical approximation of SOIs.