Synthesis and preliminary photophysical studies of intramolecular electron transfer in crown-linked donor- (chromophore-) acceptor complexes

Abstract

Among the emerging themes in chemical, biological, and photosynthetic studies of electron-transfer (ET) reactivity is the apparently essential role played by superexchange and related phenomena in facilitating long-range donor-acceptor coupling.1 Indeed, numerous recent model studies2•3 have emphasized the importance of the intervening medium-typically a covalently bound bridge-in providing energetically accessible virtual states or "conduction" pathways. Often, however, in naturally occurring ET processes the intervening medium (typically a collection of protein residues) is not directly covalently bound to either redox partner; one might question, therefore, whether modeling approaches which emphasize direct synthetic linkages can be fully successful in mimicking thoseparticular processes. An appealing alternative approach for biological redox systems involves the systematic replacement and alteration of key residues (i.e. virtual charge-transfer sites) via site-directed mutagenesis.4•5 While spectacular effects have indeed been seen, the inherent complexity of the systems themselves has sometimes precluded simple interpretations.4 We report here a new approach which, in a sense, blends elements of these two strategies. A comparatively simple family of linked donor-(chromophore-) acceptor complexes has been synthesized and photochemically characterized. The linkages themselves are saturated (and thus relatively ineffective as bridges). They are designed, however, to permit noncovalent encapsulation of real or virtual charge-transfer centers along the "line of fire" between primary donor and acceptor sites.

pH-Dependent Photophysical Behavior of Rhenium Complexes Containing Hydroxypyridine Ligands

“…One possible mechanism for this deactivation pathway is reductive quenching by the deprotonated hydroxypyridine ligand. Intramolecular electron transfer reactions in the excited state are well known, [7][8][9][10] and it is clear that the reducing power of the hydroxypyridine ligand will be enhanced by deprotonation. This is supported by the observed differences in quenching between phenol and phenolate, which correlates well with the difference in reduction potentials of approximately 200 mV.…”

Mass spectrometry of rhenium complexes: a comparative study by using LDI‐MS, MALDI‐MS, PESI‐MS and ESI‐MS

“…The transition metal complexes have been investigated, and many of them have shown that they might be utilized in electron transfer studies, solar energy conversion and catalysis . Possible applications as luminescent sensors, molecular materials for nonlinear optics or optical switching have also emerged. In particular, luminescent transition metal complexes of Re(I) and Ru(II) with polypyridil ligands have been recognized as good potential candidates for the development of pH sensing devices .…”

Fluorescent Compounds Having the Spaced and Integrated Type Receptors

“…5 upon nestling in the central cavity. 43 The reasons for this effect is currently unknown. More detailed examination of guest-induced spectral shifts and lifetime effects in this family would be welcome from a sensor perspective.…”