Degree Name

Master of Science (MS)

Semester of Degree Completion

2017

Thesis Director

Hongshan He

Abstract

During the past 20 years there has been a remarkable growth in the use of the fluorescence technique in biological studies. Fluorescence and time-resolved fluorescence spectroscopy are considered primary research tools in the field of biochemistry. Currently, fluorescence spectroscopy is a dominant methodology and used widely in biotechnology and medical diagnosis process. One impediment in using fluorescent probes is the fluorescence of biological substrates and fluorescence of diagnostic probes are significantly overlapped, and it decreases the detection sensitivity. Also, commercially available probes require UV or near-UV light excitation, causing severe degradation of biological substrates. Near-infrared emitting lanthanide complexes can overcome this problem by enhancing the detection sensitivity.

BODIPY dyes have gained significant attention in application of fluorescence sensing and imaging in recent years, because they possess many desirable properties such as high extinction coefficient, narrow absorption and emission bands, high quantum yield and low photobleaching effect. One strategy to overcome the low detection sensitivity of fluorescent dyes is; shift the absorbance and emission of BODIPY precursor towards the longer wavelength regions by increasing the π-conjugation of a sensitizer. BODIPY molecules are especially responsive to this method.

Four BODIPY-based ligands and four Yb(III) lanthanide complexes have been synthesized, which bear 5-ethynyl-5'-methyl-2,2'-N-bipyridine ligand-binding-group (LBG) in the C2 position and either a hydrogen (PH1), an iodine (PH2), an 4-ethynylbenzoic acid (PH3) or an 1-ethynyl-4-isothiocyanatobenzene (PH4) groups in its C6 position. This study focused to test their ability to sensitize the luminescence of NIR emission of Yb(III) ion. All ligands exhibited broader absorption with high molar absorption coefficients. The PH3 ligand displays maximum absorption at (573 nm). The typical metal centered luminescence is detected at 980 nm for Yb(III) upon excitation at their maximal absorption position in the visible region. All complexes showed similar lifetimes in the NIR region (10.9 - 11.1 μs), which corresponds to emission yield of 0.09%. This study demonstrates that the BODIPY-bipyridine ligands are adequate for sensitizing the luminescence of NIR-emitting lanthanide ions, allowing excitation wavelengths extending into the red region of the visible spectrum.

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