School of Chemistry - Research Publications

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Author: Gomez, Daniel × Author: Polyzos, Anastasios × End date: 2022 × Type: Journal Article ×

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    Photoexcited Pd(ii) auxiliaries enable light-induced control in C(sp3)-H bond functionalisation
    Czyz, ML ; Weragoda, GK ; Horngren, TH ; Connell, TU ; Gomez, D ; O'Hair, RAJ ; Polyzos, A (ROYAL SOC CHEMISTRY, 2020-03-07)
    Herein we report the photophysical and photochemical properties of palladacycle complexes derived from 8-aminoquinoline ligands, commonly used auxiliaries in C-H activation. Spectroscopic, electrochemical and computational studies reveal that visible light irradiation induces a mixed LLCT/MLCT charge transfer providing access to synthetically relevant Pd(iii)/Pd(iv) redox couples. The Pd(ii) complex undergoes photoinduced electron transfer with alkyl halides generating C(sp3)-H halogenation products rather than C-C bond adducts. Online photochemical ESI-MS analysis implicates participation of a mononuclear Pd(iii) species which promotes C-X bond formation via a distinct Pd(iii)/Pd(iv) pathway. To demonstrate the synthetic utility, we developed a general method for inert C(sp3)-H bond bromination, chlorination and iodination with alkyl halides. This new strategy in auxiliary-directed C-H activation provides predictable and controllable access to distinct reactivity pathways proceeding via Pd(iii)/Pd(iv) redox couples induced by visible light irradiation.
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    Luminescence of a Transition Metal Complex Inside a Metamaterial Nanocavity
    Connell, TU ; Earl, SK ; Ng, C ; Roberts, A ; Davis, TJ ; White, JM ; Polyzos, A ; Gomez, DE (John Wiley & Sons, 2017-08-25)
    Modification of the local density of optical states using metallic nanostructures leads to enhancement in the number of emitted quanta and photocatalytic turnover of luminescent materials. In this work, the fabrication of a metamaterial is presented that consists of a nanowire separated from a metallic mirror by a polymer thin film doped with a luminescent organometallic iridium(III) complex. The large spin–orbit coupling of the heavy metal atom results in an excited state with significant magnetic-dipole character. The nanostructured architecture supports two distinct optical modes and their assignment achieved with the assistance of numerical simulations. The simulations show that one mode is characterized by strong confinement of the electric field and the other by strong confinement of the magnetic field. These modes elicit drastic changes in the emitter’s photophysical properties, including dominant nanocavity-derived modes observable in the emission spectra along with significant increases in emission intensity and the total decay rate. A combination of simulations and momentum-resolved spectroscopy helps explain the mechanism of the different interactions of each optical mode supported by the metamaterial with the excited state of the emitter.