Dynamics of conformational gating and charge trapping in dendritic chromophores

Myron, Brent Donald Bruce (2012) Dynamics of conformational gating and charge trapping in dendritic chromophores. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

The research presented in this Dissertation concerns the elucidating the origin of observed photoinduced dynamics in two distinct types of dendritic chromophores. Physical phenomena such as photon absorption, radiative and non-radiative decay, Förster and Dexter energy transfer, Marcus electron transfer, and Energy Gap Law of non-radiative decay are introduced and discussed in this context. -- Following a general introduction of the physical, chemical, and photophysical properties of dendrimers, the unique excited state dynamics of a family of heteroleptic ruthenium polypyridyl complexes of the form [Ru(bpy)₂L]²⁺ (where L represents a ligand derivatized with several sizes of poly(phenylenevinylene) dendrimers) are presented and discussed. Laser flash photolysis and emission spectroscopy reveal the presence of atypical risetime kinetics and dual emission in these compounds. It is hypothesized that conformational dynamics about these dendritic groups cause profound attenuation of interligand charge transfer, leading to emission from two separate ³MLCT states. -- The second part of the research involves two families of Fréchet-type dendrimers surrounding a tris(methyl viologen) core, wherein the potent electron accepting ability of the MV²⁺* excited state drives electron transfer and long-term charge trapping. The structural features of these dendrimers that yield such long-lived charge separated states are addressed in the context of the inverted region for non-radiative decay as described by Energy Gap Law.

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