Steady-state and Time-resolved Spectroscopic Studies on Gold(I) Complexes
Date Issued
2012
Date
2012
Author(s)
Chang, Yuh-Chia
Abstract
Alkynyl gold complexes attract considerable attention due to their rich photoluminescent properties an pronounced tendency of the gold ions to form metal-metal (aurophilic) bonds, these compounds often aggregate in the solid state and in solution to give intriguing polynuclear assemblies of various structural types.
We investigate a homoleptic Au−Cu alkynyl cluster that represents an unexplored class of luminescent materials with stimuli-responsive photophysical properties. We also synthesize high-yield self-assembly of homoleptic clusters (AuC2R)10 by treatment of Au(SC4H8)Cl with stoichiometric amount of hydroxyaliphatic alkyne in the presence of NEt3. The luminescence behavior of both AuI10 and AuI8 families has been studied, revealing efficient room-temperature phosphorescence in solution and in the solid state, with the maximum quantum yield approaching 100%. DFT computational studies showed that in both AuI10 and AuI8 clusters metal-centered Au→Au charge transfer transitions mixed with some π-alkynyl MLCT character play a dominant role in the observed phosphorescence.
A series of newly synthesized diphosphine bimetallic Au(I) complexes exhibit remarkable ratiometric changes of intensity for phosphorescence versus fluorescence that are excitation wavelength dependent. This phenomenon is in stark contrast to what is commonly observed in condensed phase photophysics. The mechanism is rationalized by negligible metal d orbital contribution in the S1 state for the titled complexes. Conversely, significant ligand-to-metal charge transfer character in higher-lying excited states greatly enhances spin-orbit coupling and hence the ISC rate. The net result is to harvest high electronically excited energy toward triplet states, enhancing the phosphorescence. The above mechanism of harvesting triplet state may have numerous applications. For example, color-tunable OLED (organic light-emitting diode) devices for which the color of luminescence can be changed via altering the applied voltage may be fabricated.
We also demonstrate the feasibility of transient upconversion in this type of au complexes. The triplet state can be considered as a reservoir of excited states for a subsequent energy transfer. We can pump the complex with “green” laser(532nm) and then obtain “blue” emission(430nm) which is of particular interest due to energy issue.
Subjects
Transition metal complexes
gold
transient absorption spectra
time-resolved spectra
Type
thesis
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