Photoinduced Electron Transfer and Intramolecular Folding in a Tricarbonylrhenium (Bi)pyridine Based Donor/Crown/Acceptor Assembly:  Dependence on Solvent

Abstract

The title assembly diplays an emissive rhenium-to-pyridine charge-transfer state that is partially quenched by electron transfer to an attached acceptor (nitrobenzene). Quenching is preceded by intramolecular folding (J. Am. Chem. Soc. 1993, 115, 2048). Variable-temperature quenching measurements can be used to determine the characteristic temperature, T tr, above which unfolded photoexcited state conformations become favored over folded conformations. Similar information for the ground state can be obtained from variable-temperature NMR measurements. Studies in eight solvents show that excited state folding is (1) enthalpically favored but entropically disfavored (all solvents), (2) correlated (via T tr) with the inverse dielectric strength of the solvent, and (3) enhanced in comparison to folding in the electronic ground state (studies in one solvent). The combined evidence points to a folding reaction that is driven by optimization of localized Coulombic interactions. Optimization of solvent cohesive interactions, however, may possibly also play a role in the folding reaction.

Interactions with Aromatic Rings in Chemical and Biological Recognition

“…Thus, the apolar complexation‐promoting characteristics of water can be correlated with such characteristics of other solvents (as expressed by E T (30)) and are predictable solely on the basis of physical constants and properties. Linear free‐energy relationships with E T (30) or related empirical solvent parameters have also been useful in describing the solvent dependencies of other host–guest complexation processes,12, 48, 51 conformational reorganizations,52 and chemical transformations 53…”

Wechselwirkungen mit aromatischen Ringen in chemischen und biologischen Erkennungsprozessen

“…Demzufolge lassen sich die Eigenschaften von Wasser, das die unpolare Komplexierung vermittelt, mit den entsprechenden Eigenschaften der anderen Lösungsmittel (beschrieben durch E T (30)) korrelieren, und der Lösungsmitteleinfluss auf die Komplexbildung ist somit in allen Fällen mithilfe physikalischer Konstanten und Eigenschaften voraussagbar. Lineare‐Freie‐Energie‐Beziehungen mit E T (30) oder verwandten empirischen Lösungsmittelparametern wurden auch für die Beschreibung der Lösungsmittelabhängigkeit anderer Wirt‐Gast‐Komplexierungsprozesse,12, 48, 51 von Konformationsänderungen, die eine beträchtliche molekulare Reorganisation auslösen,52 und von chemischen Stoffumwandlungen verwendet 53…”

Luminescence behavior of tetraaza macrocylic nickel (II) complexes and non-linear Stern–Volmer quenching

“…The quenching of fluorescence exhibited by transition metal complexes [31,32] and organic compounds by nitroaromatics [33] as well as other nitro compounds [34] in different media has been reported. Similarly fluorescence quenching by nickel (II) macrocyclic complexes and emission spectral recognition of anion are also known [35,36].…”