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Title:	The structure and electronic properties of new ruthenium complexes with 1-benzoyl-3-(pyridine-2-yl)-1h-pyrazole as potential photosensitiser
Authors:	Mark Lee Wun Fui (P72599)
Supervisor:	Mohammad Kassim, Prof. Dr.
Keywords:	Electronic properties Ruthenium Photosensitiser Synthesis Universiti Kebangsaan Malaysia -- Dissertations
Issue Date:	Apr-2017
Description:	The precursor 2-(1H-pyrazol-3-yl)pyridine (pypz) ligand and benzoyl chloride have been used for the synthesis of 1-benzoyl-3-(pyridine-2-yl)-1H-pyrazole (L) ligand. Derivatives of L (R-L) with variant substituent groups (R = CH3, OCH3, Cl and Br) on the benzoyl ring at ortho, meta or para positions were also synthesised. Subsequently, the Ru(II) complex, [{Ru(bpy)2(pypz)}(PF6)2] (bpy = 2, 2'-bipyridyl), abbreviated as Ru(pypz), was synthesised from the precursor [Ru(bpy)2Cl2] (RuCl2) and pypz. However, the reaction of RuCl2 and L to obtain the desired [{Ru(bpy)2(L)}(PF6)2] (RuL) complex was unsuccessful due to the cleavage of the benzoyl moiety that occurred in L. Eventually, RuL was successfully synthesised via the reaction of Ru(pypz) with benzoyl chloride. Derivatives of [{Ru(bpy)2(R-L)}(PF6)2] complexes were synthesised accordingly with the same method. The implementation of substituent groups in L was expected to affect the structure and electronic properties of the obtained complexes. The ligands and complexes were structurally characterized on the basis of micro-elemental analysis for C, H and N, and spectroscopic techniques such as infrared (IR), ultraviolet-visible (UV-Vis), fluorescence, nuclear magnetic resonance (NMR) and mass spectroscopy (MS). Full geometry optimization and electronic structure of the ligand and complex structures were studied using density functional theory (DFT) and time-dependent (TD) DFT method with B3LYP exchange-correlation functional and 6-31G (d,p) basis-set for H, C, N, O, Cl and Br; and LAN2LDZ basis set as effective core potential for the ruthenium centre. The ligands showed an intense IR stretching frequency for C=O in the range of 1714-1679 cm-1, while in the Ru(II) complexes the characteristic v(C=O) falls in a higher frequency range (1741-1716 cm-1). In general, the UV-Vis spectra of the Ru(II) complexes exhibit a broad absorption peak due to metal (d) → ligand (pπ*) charge tranfer (MLCT) transitions (ε = 5000-10000 M-1cm-1; 0.05 mM; CH3CN), in the visible region, ca. 400-600 nm. While, the ligand-based π→π* electronic transition occurred in the UV region of the spectrum; (ε = ~30000 M-1cm-1; 0.05 mM; CH3CN). The location and energy levels of the highest occupied (HOMO) and lowest unoccupied (LUMO) molecular orbital involved in these electronic transitions are influenced by the position and types of substituent groups on the benzoyl ring. In RuL and its derivatives, the HOMO is mainly localised at the Ru(II) centre, while the LUMO is spread across the L ligand. Implementation of Ru(II) complexes as a potential panchromatic photosensitizer in a TiO2 catalysed photoelectrochemical (PEC) water splitting reaction requires matching of band energies of Ru(II) complexes, TiO2 and the water splitting potentials. Cyclic voltammetry was used to determine their redox potentials from which the band energies were calculated. Subsequently, energy band diagram of Ru(II) complexes were constructed along with TiO2 (conduction band) and water oxidation potential. The LUMO levels are strategically positioned above the conduction band of TiO2 to allow photoexcited electrons of LUMO to flow freely into the lower energy TiO2 conduction band. Therefore, Ru(II)-sensitised TiO2 photoanode demonstrated positive photoresponse towards photocurrent generation in a PEC cell.,Certification of Master's/Doctoral Thesis" is not available
Pages:	141
Publisher:	UKM, Bangi
Appears in Collections:	Faculty of Science and Technology / Fakulti Sains dan Teknologi

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