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A Strongly Luminescent Chromium(III) Complex Acid
Author(s) -
Otto Sven,
Förster Christoph,
Wang Cui,
ReschGenger Ute,
Heinze Katja
Publication year - 2018
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201802797
Subject(s) - deprotonation , luminescence , quantum yield , protonation , chemistry , photochemistry , hydroxide , hydrogen bond , pyridine , acetonitrile , ligand (biochemistry) , ion , inorganic chemistry , fluorescence , medicinal chemistry , molecule , materials science , organic chemistry , biochemistry , physics , receptor , optoelectronics , quantum mechanics
The synthesis, structure, reactivity, and photophysical properties of a novel acidic, luminescent chromium(III) complex [Cr(H 2 tpda) 2 ] 3+ ( 2 3+ ) bearing the tridentate H 2 tpda (2,6‐bis(2‐pyridylamino)pyridine) ligand are presented. Excitation of 2 3+ at 442 nm results in strong, long‐lived NIR luminescence at 782 nm in water and in acetonitrile. X‐ray diffraction analysis and IR spectroscopy reveal hydrogen‐bonding interactions of the counter ions to the NH groups of 2 3+ in the solid state. Deprotonation of the NH groups of 2 3+ by using a non‐nucleophilic Schwesinger base in CH 3 CN switches off the luminescence. Re‐protonation by using HClO 4 restores the emission. In water, the p K a value of 2 3+ amounts to 8.8, yet deprotonation is not reversible in the presence of hydroxide ions. Dioxygen quenches the emission of 2 3+ , but to a weaker extent than expected. This is possibly due to the strong ion‐pairing properties of 2 3+ even in solution, reducing the energy transfer efficiency to O 2 . Deuteration of the NH groups of 2 3+ approximately doubles the quantum yield and lifetime in water, demonstrating the importance of multiphoton relaxation in these NIR emitters.