Excited states in spatially-confined [3x3] grid-type complexes

Smith, Steven (2011) Excited states in spatially-confined [3x3] grid-type complexes. Masters thesis, Memorial University of Newfoundland.

[English] PDF - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. Download (39MB)

Abstract

The field of nanoscience is predicated on the study of organized assemblies on the nanoscale. Through an inderstanding of the unique properties of highly-ordered molecular assemblies at confined dimensions, the development of new devices can be realized. However, the challenge in the constructin of a new device involves an understanding of the properties expressed by each of the components in the combined collective. -- Previously synthesized grid-type complexes incorporate both metal ions and π-ligands into a highly-organized spatially-confined nanoscale system. The composition of the grid-type structure can vary from anarray of [2x2] metal ions with 4 ligands to [5x5] metal ions with 10 ligands. These nanostructures may be partitioned into substructures with involve a grid-like core of metal ions and a π-stacked ligand frameowrk encompassing the core. An understanding of the electronic properties of these nanostructures involves an understanding of the electronci properties of each of these substructures, and the collective electronic properties expressed through interaction of the core with the ligands. The studies presented in this thesis focuses on the phtotophysical properties of three self-assembled [3x3] grid-type systems which are compsed of Zn(II)₉, Mn(II)₉, and Mn(III)₄Mn(II)₅ metal ions and 6 hydrazon-based (2POAP) ligands. -- Comprehensive studies on [Zn(II)₉(2POAP-2H)₆](NO₃)₆ are presented which classify the excited states for the ligand framework in the gred-tytpe complexes studied. The ligands in the [3x3] grid-type complex portray both discrete and emergent charge transfer behaviour which is greatly influenced by spatial-confinement. The ligand excited states are shown to exhibit intramolecular charge transfer specific to each ligand as well as interligand charge transfer between ligands. -- Following a discussion on the ligand states, the excited states for the metal core in [Mn(II)₉(2POAP-2H)₆](ClO₄)₆ and [Mn(III)₄Mn(II)₅(2POAP-2H)₆](ClO₄)₁₀ are presented. Furthermore, the excited states resulting from the nteractin of the metal core with the ligand framework are classified. These states are shown to exhibit a range of charge transfer behaviour which includes metal-to-metal charge tgransfer, ligand-to-metal charge transfer, and metal-to-ligand charge transfer. Moreover, it is shown that the excited states in these open-shell metal complexes retain their characteristic ligand states which are offset by the interaction of the metal with the ligand. -- The light-harvesting properties of [Zn(II)₉(2POAP-2H)₆](NO₃)₆ were investigated through titrations with anthracene-9-carboxylic acid. These studies were undertaken to examine the potential application of grid-type complexes as light-harvesting units. The interaction of these molecules results in a supramolecular hydrogen-bonded adduct in which electronic excitation energy transfer is heavily involved in the excited state relaxation process. This excitation energy transfer is shown to occur from the anthracene derivative to a ligand charge transfer state over relatively short (~8 Å) and long distances of up to 50 Å through the Förster mechanism.

Actions (login required)

View Item