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Title: Synthesis and photochemical characterisation of luminescent gold complexes for technological applications
Author: Pichereau, Jeremie Guillaume
Awarding Body: Swansea University
Current Institution: Swansea University
Date of Award: 2008
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Two new precursors of dithiolate ligands, 2,6-dimercaptopyrazine (DMPA) and 2,6-dimercaptonicotinic acid (ADMN) have been synthesised and characterised. Their photochemical properties have been studied along with those of other known N-heterocyclic thiol compounds namely: (4,6-dimercaptopyrimidine (46PYRI), 2,4-dimercaptopyrimidine (24PYRI), 5,6-diamino-2,4-dimercaptopyrimidine (NPYRI) and 2,6-dimercaptopyridine (DMP)). All these compounds can be in a tautomeric equilibrium between thiol and thione forms, and it has been shown that in polar media the thioketone is the dominant species. All emit in a glass at 77 K and room temperature, but only 24PYR1 and 46PYRI give phosphorescence at 77 K (T = 380 mus and 57 mus respectively). The presence of a thiol group effectively quenches the phosphorescence and only fluorescence is observed for the other compounds. They all have an irreversible electrochemistry. The crystal structure of 46PYRI is reported for the first time. Twenty-five new binuclear gold(I) phosphine derivatives of these dithiolate ligands have been synthesised: i.e. with bis(diphenylphosphino)methane, bis(diphenylphosphino)ethane, bis(diphenylphosphino)propane and bis(diphenylphosphino)butane, for annular complexes, or with triphenylphosphine for open ring compounds. A mononuclear triphenylphosphinegold(I) complex with DMP is also reported. Gold-gold interactions were absent from the two crystal structures obtained. All these compounds show phosphorescence in the solid state at RT and in a glass at 77 K, but only complexes with DMP as dithiolate emit in solution at RT (through phosphorescence also). The origin of the luminescence is thought to be from a mixture of LMCT or ILCT excited states. Complexes with electron-withdrawing groups (e.g. ADMN) on the thiolate promote the ILCT excited state whereas electron-donating groups (e.g. NPYRI) promote the LMCT excited state. All complexes studied gave irreversible electrochemistry. Ab initio studies on the dithiols confirm the greater stability of the thioketone form in polar solvents. Structural simulations of the binuclear gold(I) complexes confirm both the absence of an aurophilic interaction and the origin of luminescence.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available