Michael D. Hopkins

Bio: Michael D. Hopkins is an academic researcher from California Institute of Technology. The author has contributed to research in topics: Excited state & Ground state. The author has an hindex of 3, co-authored 4 publications receiving 158 citations.

Electrochemistry and electrogenerated chemiluminescence of Mo2Cl4(PMe3)4

Abstract: The electrochemical behavior and electrogenerated chemiluminescence (ecl) of Mo/sub 2/Cl/sub 4/(PMe/sub 3/)/sub 4/ in tetrahydrofuran and acetonitrile solutions have been investigated. Oxidation to the +1 cation and reduction to the -1 anion occur in quasi-reversible and reversible cyclic voltammetric waves, respectively. The oxidation product undergoes a subsequent chemical reaction, while the reduction product is stable. Emission is produced by the electron-transfer reaction between the +1 and -1 species; this emission is characteristic of /sup 1/(deltadelta/sup */) Mo/sub 2/Cl/sub 4/(PMe/sub 3/)/sub 4/ with emission lambda/sub max/ 680 nm. The ecl efficiency (photons produced per electron consumed) is 0.002. Electrogenerated chemiluminescence has been observed in acetonitrile solution by the reaction of electrogenerated Mo/sub 2/Cl/sub 4/(PMe/sub 3/)/sub 4//sup -/ with the strongly oxidizing intermediate, SO/sub 4//sup -/, generated by reduction of S/sub 2/O/sub 8//sup 2 -/.

Chemistry of Personalized Solar Energy

Abstract: Personalized energy (PE) is a transformative idea that provides a new modality for the planet’s energy future. By providing solar energy to the individual, an energy supply becomes secure and available to people of both legacy and nonlegacy worlds and minimally contributes to an increase in the anthropogenic level of carbon dioxide. Because PE will be possible only if solar energy is available 24 h a day, 7 days a week, the key enabler for solar PE is an inexpensive storage mechanism. HY (Y = halide or OH−) splitting is a fuel-forming reaction of sufficient energy density for large-scale solar storage, but the reaction relies on chemical transformations that are not understood at the most basic science level. Critical among these are multielectron transfers that are proton-coupled and involve the activation of bonds in energy-poor substrates. The chemistry of these three italicized areas is developed, and from this platform, discovery paths leading to new hydrohalic acid- and water-splitting catalysts are...

Occurrence, mechanisms and analytical applications of electrogenerated chemiluminescence. A review

Abstract: The occurrence, mechanisms, and practicalities of the electrogeneration of chemiluminescence are described with reference to applications in analytical chemistry. The general theory of electron transfer excitation mechanisms is discussed with respect to organic reactions in aprotic media, and extended to include inorganic complexes and clusters. Analytical applications are classified according to the excitation mechanism, i.e., organic and inorganic systems, established chemiluminescence reactions initiated electrochemically, and cathodic luminescence at semiconductor electrodes.

Review—Electrogenerated Chemiluminescence: Light Years Ahead

Abstract: An overview is given on great achievements in electrogenerated chemiluminescence or electrochemiluminescence (ECL) by Allen J. Bard. The established ECL theories and fundamentals are first described. The developed analytical instrumentation and methodology for ECL are then revealed. Studies of various types of ECL luminophores are summarized. The discovered ECL applications especially in bioanalysis and bioimaging are finally depicted. Bard's presentations and publications on ECL are indispensable resources of inspiration and guides for ECL researchers worldwide, who will further advance ECL research and applications already in a prosperous stage.

Studies of electronic coupling and mixed valency in metal-metal quadruply bonded complexes linked by dicarboxylate and closely related ligands.

Abstract: Complexes of the form [(tBuCO2)3M2]2(mu-O2C-X-CO2), where M is Mo or W and X is a pi conjugated organic group, are ideally suited for studies of electronic coupling between the two redox centers via M2 delta-bridge pi conjugation. The complexes have intense metal-to-bridge charge-transfer transitions in the visible or near-IR region of the spectrum and exhibit thermo-, solvato- and electrochromic behavior. Chemical oxidation results in the formation of mixed-valence species that are particularly well-suited for the study of the class II/III border. The extent of electronic coupling is determined by a variety of spectroscopic techniques and, in particular, by EPR and electronic absorption spectroscopy. The latter provides a direct measure of the electronic coupling parameter Hab in pairs (Mo and W) of otherwise identical complexes. Similarly, the substitution within the bridge of the CO2 group by COS or RNCO allows an evaluation of the mechanism of the electronic coupling in closely related complexes. Electronic structure calculations employing density functional theory complement frontier molecular orbital theory in the interpretation of the physicochemical properties of these complexes.

Quintuply‐Bonded Dichromium(I) Complexes Featuring Metal–Metal Bond Lengths of 1.74 Å

Abstract: The construction of a metal–metal quintuple bond has long been a challenge for chemists, since a large number of quadruple-bonded dinuclear complexes have been reported and their bonding and electronic structures extensively investigated and well understood. On the basis of theoretical work, many possible structures could be capable of accommodating a metal–metal quintuple bond, in contrast to the strict requirement of having twometal atoms embraced by eight ligands in a tetragonal geometry for a metal–metal quadruple bond. Of particular interest is that all of these model structures display a common feature: a low-coordinate environment around metal centers. From a practical point of view, the first quintuple-bonded dichromium complex [Ar’CrCrAr’] (Ar’=C6H3-2,6-(C6H3-2,6-iPr2)2, Cr Cr= 1.8351(4) ), which adopts a trans-bent geometry, was reported by Power and co-workers in 2005. More recently, in 2007, Theopold and co-workers reported an interesting dichromium complex supported by a-diimines, [Cr2(m-h -{C(H)N(C6H3-2,6-iPr2)}2)2], which was shown by computations to exhibit some degree of Cr Cr quintuplebond character. Since our first report on the characterization of an unconventional quadruple-bonded dimolybdenum complex [Mo2{m-h -(DippN)2SiMe2}2], where each Mo atom is ligated by only two nitrogen donors, we have been interested in the pursuit of low-coordinate and multiply-bonded dinuclear complexes. We recently characterized a mixed-valent dichromium complex stabilized by three amidinate ligands, [Cr2{ArNC(H)NAr}3] (Ar = 2,6-C6H3(CH3)2), and its oneelectron reduction partner [Cr2{Ar NC(H)NAr}3] , which exhibited the shortest metal–metal bond length of 1.7397(9) . Qualitatively, the latter is believed to incorporate a Cr Cr quintuple bond. In view of Power s and Theopold s complexes, wherein both Cr centers were coordinated by two donor atoms, we set out to prepare dichromium bis(amidinato) complexes, from which metal–metal quintuple bonds are expected. Herein we report a series of complexes of the form [Cr2{m-h -ArNC(R)NAr}2], which all exhibit very short Cr Cr quintuple-bond lengths of approximately 1.74 . Amidinate ligands, featuring substituents of different bulk, are used to stabilize these Cr Cr quintuple bonds. Prior to the synthesis of the target molecules, four green mononuclear complexes, 1a–d, of the form [CrCl2(thf)2{h ArNC(R)NAr}] were prepared in good yields by treatment of [CrCl3(thf)3] or CrCl3 with lithiated amidines (Scheme 1, see