Spectroscopic aspects for the Yb3+ coordination compound with a large energy gap between the ligand and Yb3+ excited states

• Published in: Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy Molecular and biomolecular spectroscopy, 2022-06, Vol.274, p.121072, Article 121072
• Main Authors: Kasprzycka, Ewa, Carneiro Neto, Albano N., Trush, Viktor A., Malta, Oscar L., Jerzykiewicz, Lucjan, Amirkhanov, Vladimir M., Legendziewicz, Janina, Gawryszewska, Paula
• Format: Article
• Language: English
• Subjects: Absorption spectroscopy; Energy transfer; Luminescence; N-phosphorylated sulfonamide; Theoretical calculations; Ytterbium
• ISSN: 1386-1425
• DOI: 10.1016/j.saa.2022.121072

[Display omitted] •The spectroscopic data are essential for the use of the theoretical model.•The energy gap between the ligand and Yb excited states is large.•The theoretical model shed light on the ligand-to-Yb energy transfer phenomenon.•The theoretical model used allows to estimate the quantum yield of the Yb emission.•The charge transfer state plays an important role in the energy transfer process. We present the experimental and theoretical results that made it possible to propose the energy transfer mechanism for a Yb complex with a large energy gap between the ligand and Yb excited states using a theoretical model and experimental data. Absorption and emission spectroscopy in the 300–4 K range is used for the study of the Yb3+ compound with N-phosphorylated sulfonamide (Na[YbL4]), which, despite the large energy gap, is characterized by high emission sensitization efficiency (ηsens = 40%) and relatively long Yb3+ emission lifetime (27 μs). The crystal structure of Na[YbL4], radiative lifetime (930 μs), refractive index (1.46), intrinsic (3.0%), and overall (1.3%) emission quantum yield were determined. To obtain the electronic properties of the Na[YbL4], a time-dependent density functional theory (TD-DFT) was performed. The intramolecular energy transfer (IET) rates from the excited states S1 and T1 to the Yb3+ ion as well as between the ligand and the ligand-to-metal charge transfer (LMCT) states were calculated. Once the intersystem crossing S1 → T1 is not so effective due to a large energy gap between S1 and T1 (≈10000 cm−1), it has been shown that the LMCT state acts as an additional channel to feed the T1 state. Then, the T1 can transfer energy to the Yb3+ 2F5/2 energy level (WT), where WT is dominated by the exchange mechanism. Based on IET and a rate equation model, the overall emission quantum yield QLLn was simulated with and without the LMCT, this also confirmed that the pathway S1 → LMCT → T1 → Yb3+ is more likely than the S1 → T1 → Yb3+ one.