Synthesis, characterization and photophysical studies of triazine-based lanthanide(III) β-diketonate complexes

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Synthesis, characterization and photophysical studies of triazine-based lanthanide(III) β-diketonate complexes

 

Author: Lo, Wai Sum
Title: Synthesis, characterization and photophysical studies of triazine-based lanthanide(III) β-diketonate complexes
Degree: Ph.D.
Year: 2016
Subject: Rare earth metals.
Rare earth metals -- Spectra.
Hong Kong Polytechnic University -- Dissertations
Department: Dept. of Applied Biology and Chemical Technology
Pages: 279 pages : color illustrations
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b2929125
URI: http://theses.lib.polyu.edu.hk/handle/200/8791
Abstract: A review on the general background, coordination properties and optical properties of trivalent lanthanides is presented, with particular emphasis on their characteristic photoluminescent properties. Ln(III) are excellent emitters which cover most regions of the visible spectrum and extend to the near-infra red (NIR) region, with long lifetimes and distinctive emission profiles. However, their poor ability to absorb light means an external antenna is required to channel excited energy prior to radiative deactivation and careful design of the ligand system is necessary to minimize numerous competitive non-radiative processes. This work encompasses the photophysical studies of europium(III), samarium(III) and ytterbium(III) complexes in a bi-chromophoric system. The well-known chelate - and sensitizer - 2-thenoyltrifluoroacetate (TTA) and a 1,3,5-triazine-based tridentate ligand complements the coordination of the trivalent lanthanides. The incorporation of an N,N-diethylanilinyl moiety imparts intraligand charge transfer (ILCT) character to the tridentate ligand which will be discussed following the general syntheses of various ligands and complexes in Chapter 3. Chapter three focuses on the visible luminescence from the Eu(III) and Sm(III) complexes and evaluates the sensitization efficiencies and quantum efficiencies between the TTA and ILCT antennae. As ILCT transitions are solvatochromic, the photophysical properties were measured in various solvents and discussed in details. It was found that in non-polar solvents such as benzene, the luminescence quantum yield of the Sm(III) complexes are quite high compared to literature.
As Sm(III) is dual-emissive - emitting in both the visible and NIR regions, the NIR photophysical properties were investigated. Originating from the same emitting state as the visible luminescence transitions, the NIR transitions were studied and compared. In addition to solvatochromic studies, this chapter discusses the validity of the energy gap law in estimating the extent of quenching by high energy oscillators and thus provide a blueprint for maximizing the intrinsically weak NIR luminescence by manipulating the coordination environment. NIR luminescence from the ytterbium(III) complex was also presented, as the energy transfer mechanism of Yb(III) has always been sort of an enigma due to the large energy difference between the Yb(III) only excited state and the donating state of common antennae. Chapter five focuses on the syntheses of a multidentate water-soluble pocket for lanthanide(III) complexes. The ligand system extends the aforementioned studies by using a single multi-chelate in place of multiple tri-/bi-dentate ligands as an effort to increase the stability of the complexes in solution state and thus creates a platform for exploring the non-triplet ILCT energy transfer pathway for lanthanide(III) luminescence sensitization in water to expand the scope of potential applications.

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