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Authors: Otto, Sven Fabian
Title: Molecular rubies: novel spin-flip NIR-emitter : synthesis, understanding and first applications
Online publication date: 26-Jul-2018
Year of first publication: 2018
Language: english
Abstract: Near infrared (NIR) emissive compounds are of great interest for many applications ranging from (O)LEDs and laser media over fiber optics and security inks to optical chemical sensors. The latter in particular requires molecular and soluble emitters, a role filled at most times by complexes of rare earth or precious metals. Even though it is very challenging to achieve emission from earth abundant metal complexes, it recently is, due the high price and scarcity of the currently employed materials, a rapidly growing field of research. This work describes the development of a new class of strong NIR emitter, based on chromium(III). The presented chromium(III) complexes feature luminescence quantum yields up to 11 % in water and up to 30 % if the ligand is deuterated, with life-times of close to a millisecond (more than two milliseconds in the deuterated cases). Due to the spin-flip nature of the emission, the emission bands are exceptionally sharp. First applications of these new emitters have also been explored. The dual emission of [Cr(ddpd)2]3+ allows the measurement of temperature in solution and nanoparticles without a reference, since the emissive states are in a thermal equilibrium and the emission bands are well resolved. Further promising sensing applications include the detection of molecular oxygen by the quenching of the phosphorescence and the measurement of pressure, due to a strong red shift of the emission bands upon applied pressure. The luminescence quenching by molecular oxygen, has further been exploited for the photocatalytic production of singlet oxygen. This has been used in situ for the oxidation of tertiary, aliphatic amines and their subsequent reaction with cyanide gave α-amino-nitriles in good yields. The strong emission of [Cr(H2tpda)2]3+ is quenched by deprotonation and can, in the absence of water, be recovered by re-protonation. To fully understand the involved excited states and supplement the experimental data, theoretical methods have been employed. These include density functional theory as well as ab initio calculations. Furthermore, the zinc(II) complex [Zn(ddpd)2]2+ has been investigated. It enters an equilibrium with [ZnCl4]2– and [ZnCl2(ddpd)] in the presence of chloride ions, as a result of the d10 ions coordination diversity and the ligands flexibility. Also structurally interesting is the first mononuclear gold(II) complex [Au(tpp)], synthesized and characterized by Sebastian Preiß. High level DFT calculations could verify the second order Jahn-Teller distortion arising from the relativistic contraction of the metals 6s orbital.
DDC: 540 Chemie
540 Chemistry and allied sciences
Institution: Johannes Gutenberg-Universität Mainz
Department: FB 09 Chemie, Pharmazie u. Geowissensch.
Place: Mainz
URN: urn:nbn:de:hebis:77-diss-1000021577
Version: Original work
Publication type: Dissertation
License: In Copyright
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Extent: xvi, 320 Seiten
Appears in collections:JGU-Publikationen

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