Long-range photoinduced through-bond electron transfer and radiative recombination via rigid nonconjugated bridges: distance and solvent dependence
01 May 1987-Journal of the American Chemical Society (American Chemical Society)-Vol. 109, Iss: 11, pp 3258-3269
TL;DR: In this article, a series of molecules was synthesized containing a 1,4-dimethoxynaphthalene donor (D) and an 1,1-dicyanoethylene acceptor (a) interconnected by five different, rigid, nonconjugated bridges.
Abstract: A series of molecules 1 was synthesized containing a 1,4-dimethoxynaphthalene donor (D) an a 1,1-dicyanoethylene acceptor (a) interconnected by five different, rigid, nonconjugated bridges. The length of the bridges varies with increments of two sigma-bonds from four in 1(4) to 12 sigma-bonds in 1(12), to provide donor-acceptor center-to-center separations (R/sub c/) ranging from 7.0-14.9 A. In solvents of medium and high polarity, excitation of the donor D is followed by rapid intramolecular electron transfer. The rate constant (k/sub et/) shows only small dependence upon the solvent polarity (a factor of 2-3 between benzene and acetonitrile, for example) but decreases with increasing separation ranging from >10/sup 11/ s/sup -1/ for a four-bond separation to approx. =4 x 10/sup 8/ s/sup -1/ for a 12-bond separation. In saturated hydrocarbon solvents photoinduced electron transfer is not observed for 10 and 12-bond separations, while it is not significantly decreased for the shorter homologues. Therefore the absence of electron transfer at 10- and 12-bond separations in saturated hydrocarbon solvents is attributed to a thermodynamic rather than to a kinetic effect. In solvents where electron transfer is thermodynamically feasible, its rate is considerably greater than that found from various other experimental studies where either different bridgesmore » were used or intermolecular electron transfer was studied. Through-bond interaction involving sigma/..pi.. interaction between the bridge and the donor-acceptor pair is proposed to explain the very high electron transfer rates observed in 1; this is qualitatively correlated with independent information about this coupling derived from both theory and experiment (photoelectron spectroscopy).« less
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TL;DR: This review considers only polynuclear transition metal complexes that can be defined as supramolecular species and that are reported to exhibit luminescence and redox properties, and reviews several interesting systems such as polymer-appended metal.
Abstract: Great attention is currently paid to the synthesis of polynuclear transition metal complexes and the study of their photochemical, photophysical, and electrochemical properties. This interest is stimulated, in particular, by attempts to design and construct multicomponent systems (often called supramolecular species) capable of performing useful lightand/or redox-induced functions.1-16 A great deal of investigations on mononuclear transition metal complexes had previously shown that several families of these compounds are very interesting from the electrochemical, photochemical, and photophysical viewpoints.17-22 The metalligand interaction, in fact, is often (i) weak enough to allow the manifestation of intrinsic properties of metal and ligands (e.g., ligand-centered and metalcentered absorption bands and redox waves) and, at the same time, (ii) strong enough to cause the appearance of new properties, characteristic of the whole compound (e.g., metal-to-ligand or ligand-tometal charge-transfer bands). On passing from mononuclear to polynuclear transition metal complexes, the situation becomes even more interesting because in the latter (supramolecular) compounds one can find, besides properties related to each metal-based component, properties related to the structure and composition of the whole array. A suitable choice of the mononuclear building blocks and bridging ligands and an appropriate design of the (supramolecular) structure can in fact allow the occurrence of very interesting and potentially useful processes such as energy transfer along predetermined pathways, photoinduced charge separation, multielectron exchange at a predetermined potential, etc. The knowledge on the luminescence and redox properties of polynuclear transition metal complexes is rapidly accumulating, but it is disperse in a great number of journals. We have made an attempt to collect the available results, and we present them together with some fundamental introductory concepts and a few comments. One of the main problems, of course, was to delimit the field of this review. Using personal criteria which are related to our own research interests, we decided to consider only polynuclear transition metal complexes that can be defined as supramolecular species (section 2.2) and that are reported to exhibit luminescence. For such compounds only, the electrochemical properties have also been reviewed. Furthermore, we decided to include only classical (Werner-type) polynuclear transition metal compounds where the number of metal-based units is exactly known and the connection between the metal centers is provided only by bridging ligands. Thus, a number of interesting systems such as polymer-appended metal † In memoriam of Mauro Ciano. 759 Chem. Rev. 1996, 96, 759−833
2,076 citations
TL;DR: An overview of the design principles underlying small fluorescent probes that have been applied to the ratiometric detection of various analytes, including cations, anions, and biomolecules in solution and in biological samples are provided.
Abstract: Quantitative determination of specific analytes is essential for a variety of applications ranging from life sciences to environmental monitoring. Optical sensing allows non-invasive measurements within biological milieus, parallel monitoring of multiple samples, and less invasive imaging. Among the optical sensing methods currently being explored, ratiometric fluorescence sensing has received particular attention as a technique with the potential to provide precise and quantitative analyses. Among its advantages are high sensitivity and inherent reliability, which reflect the self-calibration provided by monitoring two (or more) emissions. A wide variety of ratiometric sensing probes using small fluorescent molecules have been developed for sensing, imaging, and biomedical applications. In this research highlight, we provide an overview of the design principles underlying small fluorescent probes that have been applied to the ratiometric detection of various analytes, including cations, anions, and biomolecules in solution and in biological samples. This highlight is designed to be illustrative, not comprehensive.
1,243 citations
TL;DR: Theoretical predictions of an "inverted region," where increasing the driving force of the reaction will decrease its rate, have begun to be experimentally confirmed and a predicted nonlinear dependence of ET rates on the polarity of the solvent has also been confirmed.
Abstract: Intramolecular long-distance electron transfer (EI) has been actively studied in recent years in order to test existing theories in a quantitative way and to provide the necessary constants for predicting ET rates from simple structural parameters. Theoretical predictions of an "inverted region," where increasing the driving force of the reaction will decrease its rate, have begun to be experimentally confirmed. A predicted nonlinear dependence of ET rates on the polarity of the solvent has also been confirmed. This work has implications for the design of efficient photochemical charge-separation devices. Other studies have been directed toward determining the distance dependence of ET reactions. Model studies on different series of compounds give similar distance dependences. When different stereochemical structures are compared, it becomes apparent that geometrical factors must be taken into account. Finally, the mechanism of coupling between donor and acceptor in weakly interacting systems has become of major importance. The theoretical and experimental evidence favors a model in which coupling is provided by the interaction with the orbitals of the intervening molecular fragments, although more experimental evidence is needed.
1,125 citations
TL;DR: In this article, the authors proposed a model for medium reorganization and donor-acceptor coupling for long-range and multicenter Electron Transfer in the gas phase.
Abstract: Electron Transfer Past and Future (R Marcus) Electron Transfer Reactions in Solution: A Historical Perspective (N Sutin) Electron Transfer--From Isolated Molecules to Biomolecules (M Bixon & J Jortner) Charge Transfer in Bichromophoric Molecules in the Gas Phase (D Levy) Long--Range Charge Separation in Solvent--Free Donor--Bridge--Acceptor Systems (B Wegewijs & J Verhoeven) Electron Transfer and Charge Separation in Clusters (C Dessent, et al) Control of Electron Transfer Kinetics: Models for Medium Reorganization and Donor--Acceptor Coupling (M Newton) Theories of Structure--Function Relationships for Bridge--Mediated Electron Transfer Reactions (S Skourtis & D Beratan) Fluctuations and Coherence in Long--Range and Multicenter Electron Transfer (G Iversen, et al) Lanczos Algorithm for Electron Transfer Rates in Solvents with Complex Spectral Densities (A Okada, et al) Spectroscopic Determination of Electron Transfer Barriers and Rate Constants (K Omberg, et al) Photoinduced Electron Transfer Within Donor--Spacer--Acceptor Molecular Assemblies Studied by Time--Resolved Microwave Conductivity (J Warman, et al) From Close Contact to Long--Range Intramolecular Electron Transfer (J Verhoeven) Photoinduced Electron Transfers Through sigma Bonds in Solution (N--C Yang, et al) Indexes
800 citations
TL;DR: This tutorial review presented some recent developments in the construction and applications of cassettes based on resonance energy transfer between fluorescent dyes in the visible and infrared region, and focused on the contributions of different connections between the energy donor and acceptor according to the " through-space" and "through-bond" methods.
Abstract: This tutorial review presents some recent developments in the construction and applications of cassettes based on resonance energy transfer between fluorescent dyes in the visible and infrared region. We focused on the contributions of different connections between the energy donor and acceptor according to the “through-space” and “through-bond” methods, and emphasised their applications in ratiometric sensing for the detection of ions and small molecules.
729 citations