Structure and Luminescence Properties of Lutetium(Iii) Complexes with 5,10,15,20-Tetraphenylporphine and its Derivatives
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Journal of Applied Spectroscopy, Vol. 87, No. 5, November, 2020 (Russian Original Vol. 87, No. 5, September–October, 2020)
STRUCTURE AND LUMINESCENCE PROPERTIES OF LUTETIUM(III) COMPLEXES WITH 5,10,15,20-TETRAPHENYLPORPHINE AND ITS DERIVATIVES M. P. Tsvirko,a* B. Kalota,a* A. Mikus,b and S. Ostrowskib
UDC 535.372+535.373
The spectral and luminescent properties of new complexes of lutetium(III)–chloride with 5,10,15,20-tetraphenylporphine and its mono-nitrophenyl derivative with a para-nitro group on one of the meso-phenyl rings were studied. The complexes showed weak fluorescence (φfl = 5·10–4) and moderate phosphorescence (φphosph = 3·10–2) at 77 K and phosphorescence at room temperature. The type of extra ligand (monodentate chloride and bidentate acetylacetonate) and the presence of an electron-withdrawing NO2 group on the meso-phenyl ring did not have an appreciable effect on the photophysics of the Lu(III)-porphyrins. The phosphorescence spectra of the complexes were shifted to the long-wavelength region. The phosphorescence lifetimes were longer (2800–3100 μs) than those of the known oxygen sensors Pt(II)- or Pd(II)-porphyrins. The oxygen determination limit in solution was estimated from quenching of the Lu(III)-porphyrin phosphorescence. Keywords: porphyrins, lutetium complexes, inorganic axial ligand, oxygen sensor, fluorescence, phosphorescence. Introduction. Practical applications of lanthanide(III)-porphyrins have attracted increasing interest in the last few decades [1–4]. Previously, applications were based mainly on f–f-luminescence of Yb(III)-, Nd(III)-, and Er(III)-porphyrins in the near-IR (NIR) region. The quantum yields of the f–f-luminescence of these complexes are comparatively low (0.1–0.5%) [5, 6]. Molecular π-π*-fluorescence and phosphorescence of Lu(III)- and Gd(III)-porphyrins without f–fluminescence has opened new possibilities. Molecular luminescence of Lu(III)- and Gd(III)-porphyrins is attractive for analytical applications because of the large Stokes shift (~180 nm) and the rather high quantum yield of NIR phosphorescence at room temperature [7–10]. Furthermore, the porphyrin ligand is amenable to numerous modifications of the complex structure and, correspondingly, flexible regulation of the chelate photophysical and chemical properties. This opens new possibilities for designing oxygen luminophore-sensors for various applications. Lanthanide(III)-porphyrins usually include a monodentate, bidentate, or tridentate axial ligand, e.g., Cl, acetylacetonate (acac), or hydro-tris(1-pyrazolyl)borate (Tr), respectively [2]. Bidentate or tridentate axial ligands are often used for NIRluminescent lanthanide(III)-porphyrins [Yb(III) Nd(III), Er(III)] to prevent addition of a solvent molecule, e.g., H2O, to the Ln3+ ion [4]. Structure determinations of Ln(III)-porphyrins with a monodentate axial ligand led to the conclusion that a solvent molecule (DMF or THF) could enter the Ln3+ coordination sphere [1, 2]. Phosphorescing meso-substituted Lu(III)and Gd(III)-porphyrins containing acac as an
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