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ABSTRACT: A unified picture is presented of water interacting with pyridine, pyridazine, pyrimidine, and pyrazine on the S(1) manifold in both gas-phase dimers and in aqueous solution. As (n,π*) excitation to the S(1) state removes electrons from the ground-state hydrogen bond, this analysis provides fundamental understanding of excited-state hydrogen bonding. Traditional interpretations view the excitation as simply breaking hydrogen bonds to form dissociated molecular products, but reactive processes such as photohydrolysis and excited-state proton coupled electron transfer (PCET) are also possible. Here we review studies performed using equations-of-motion coupled-cluster theory (EOM-CCSD), multireference perturbation theory (CASPT2), time-dependent density-functional theory (TD-DFT), and excited-state Monte Carlo liquid simulations, adding new results from symmetry-adapted-cluster configuration interaction (SAC-CI) and TD-DFT calculations. Invariably, gas-phase molecular dimers are identified as stable local minima on the S(1) surface with energies less than those for dissociated molecular products. Lower-energy biradical PCET minima are also identified that could lead to ground-state recombination and hence molecular dissociation, dissociation into radicals or ions, or hydration reactions leading to ring cleavage. For pyridine.water, the calculated barriers to PCET are low, suggesting that this mechanism is responsible for fluorescence quenching of pyridine.water at low energies rather than accepted higher-energy Dewar-benzene based "channel three" process. Owing to (n,π*) excitation localization, much higher reaction barriers are predicted for the diazines, facilitating fluorescence in aqueous solution and predicting that the as yet unobserved fluorescence from pyridazine.water and pyrimidine.water should be observable. Liquid simulations based on the assumption that the solvent equilibrates on the fluorescence timescale quantitatively reproduce the observed spectral properties, with the degree of (n,π*) delocalization providing a critical controlling factor.
Physical Chemistry Chemical Physics 04/2012; 14(25):8791-802. · 3.57 Impact Factor
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ABSTRACT: We consider the quantum entanglement of the electronic and vibrational degrees of freedom in molecules with tendencies towards double welled potentials. In these bipartite systems, the von Neumann entropy of the reduced density matrix is used to quantify the electron-vibration entanglement for the lowest two vibronic wavefunctions obtained from a model Hamiltonian based on coupled harmonic diabatic potential-energy surfaces. Significant entanglement is found only in the region in which the ground vibronic state contains a density profile that is bimodal (i.e., contains two separate local maxima). However, in this region two distinct types of density and entanglement profiles are found: one type arises purely from the degeneracy of energy levels in the two potential wells and is destroyed by slight asymmetry, while the other arises through strong interactions between the diabatic levels of each well and is relatively insensitive to asymmetry. These two distinct types are termed fragile degeneracy-induced entanglement and persistent entanglement, respectively. Six classic molecular systems describable by two diabatic states are considered: ammonia, benzene, BNB, pyridine excited triplet states, the Creutz-Taube ion, and the radical cation of the "special pair" of chlorophylls involved in photosynthesis. These chemically diverse systems are all treated using the same general formalism and the nature of the entanglement that they embody is elucidated.
The Journal of chemical physics 12/2011; 135(24):244110. · 3.09 Impact Factor
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ABSTRACT: Density functional theory structure calculations at 0 K and simulations at 300 K of observed high-resolution in situ scanning tunneling microscopy (STM) images reveal three different atomic-interface structures for the self-assembled monolayers (SAMs) of three isomeric butanethiols on Au(111): direct binding to the Au(111) surface without pitting, binding to adatoms above a regular surface with extensive pitting, and binding to adatoms with local surface vacancies and some pitting. Thermal motions are shown to produce some observed STM features, with a very tight energy balance controlling the observed structures. Variation of the degree of substitution on the α carbon is found to significantly change the relative energies for interaction of the different types of adatom structures with the surface, while the nature of the surface cell, controlled primarily by inter-adsorbate steric interactions, controls substrate reorganization energies and adsorbate distortion energies. Most significantly, by manipulating these features, chemical control of the adsorbate can produce stable interfaces with surface pitting eliminated, providing new perspectives for technological applications of SAMs.
Journal of the American Chemical Society 08/2011; 133(38):14856-9. · 9.91 Impact Factor
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ABSTRACT: A novel application of intramolecular base catalysis confers enhanced reaction rates for aminolysis ligations between peptide thioesters and peptides bearing N-terminal aspartate or glutamate residues. The broad scope of this process and its application in the total synthesis of the diabetes drug exenatide is demonstrated.
Organic Letters 08/2011; 13(18):4770-3. · 5.86 Impact Factor
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ABSTRACT: Scanning-tunneling microscopy (STM) under electrochemical control (in situ STM) in aqueous solution, combined with a priori density functional theory (DFT) image simulations at room temperature, reveals the atomic nature of the interface between Au(111) and self-assembled monolayers (SAMs) of 1-propanethiol and 1-butanethiol. Use of single-crystal gold substrates allows for both high-resolution images of the surface cell internal structure and the evaluation of pit densities on large surface terraces, while room-temperature STM image simulations facilitate discrimination between possible atomic interface structures. For both adsorbates, the high-coverage c(4 × 2) phase is identified as (3 × 2√3)-4, while the medium-coverage striped phase of 1-propanethiol SAMs is identified as (7 × √3)-4. All of these structures contain two adatom-bound adsorbates of the form RS–Au–SR (R = CnH2n+1S•) per surface unit cell. The observed pit coverages of 2.8–4.0% are much less than those typically found for methanethiol SAMs (ca. 12–20%), indicating that one of the two gold adatoms per cell in 1-propanethiol and 1-butanethiol SAMs is extracted to form a local surface vacancy rather than a coalesced surface pit. The surface vacancy appears free to diffuse within each cell on the STM time scale, with only small STM image changes associated with vacancy localization. Significantly, the c(4 × 2) phases of 1-propanethiol and 1-butanethiol SAMs give quite different STM images. 1-Butanethiol SAMs show characteristics similar to those of longer linear alkanethiols with four bright spots per cell, while the 1-propanethiol SAM displays five bright spots organized in a different pattern. These differences are rationalized by a more uniform vacancy distribution and rigid structure for 1-butanethiol SAMs, compared to the different diffusionally labile vacancy configurations and higher lateral S–C–C–C conformational flexibility found for 1-propanethiol. Also, the differences in interface structure from that of methanethiol SAMs are rationalized in terms of varying pit coalescence energies. These subtle differences underline the striking diversity in the electronic and molecular structural packing even within a single class of closely related molecular adsorbates.
The Journal of Physical Chemistry C 05/2011; 115:10630-10639. · 4.80 Impact Factor
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Katja B Heine,
Jack K Clegg,
Axel Heine,
Kerstin Gloe,
Karsten Gloe,
Thomas Henle,
Gert Bernhard,
Zheng-Li Cai, Jeffrey R Reimers,
Leonard F Lindoy,
Jochen Lach,
Berthold Kersting
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ABSTRACT: The metal complexation properties of the naturally occurring Maillard reaction product isomaltol HL(2) are investigated by measurement of its stability constants with copper(II), zinc(II), and iron(III) using potentiometric pH titrations in water, by structural and magnetic characterization of its crystalline complex, [Cu(L(2))(2)]·8H(2)O, and by density functional theory calculations. Strong complexation is observed to form the bis(isomaltolato)copper(II) complex incorporating copper in a typical (pseudo-)square-planar geometry. In the solid state, extensive intra- and intermolecular hydrogen bonding involving all three oxygen functions per ligand assembles the complexes into ribbons that interact to form two-dimensional arrays; further hydrogen bonds and π interactions between the furan moiety of the anionic ligands and adjacent copper(II) centers connect the complexes in the third dimension, leading to a compact polymeric three-dimensional (3D) arrangement. The latter interactions involving copper(II), which represent an underappreciated aspect of copper(II) chemistry, are compared to similar interactions present in other copper(II) 3D structures showing interactions with benzene molecules; the results indicate that dispersion forces dominate in the π system to chelated copper(II) ion interactions.
Inorganic Chemistry 02/2011; 50(4):1498-505. · 4.60 Impact Factor
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ABSTRACT: Low- and high-resolution absorption and fluorescence emission Q(y) spectra of bacteriochlorophyll a (BChl a) were recorded, along with homogeneous band line shapes, revealing significant asymmetry between the absorption and emission profiles that are interpreted using a priori spectral calculations. The spectra were recorded in a range of organic solvents facilitating both penta- and hexa-coordination of Mg at ambient and cryogenic temperatures. Detailed vibrational structure in the ground electronic state, virtually independent of Mg coordination, was revealed at 4.5 K by a hole-burning fluorescence line-narrowing technique, complementing the high-resolution spectrum of the excited state measured previously by hole burning to provide the first complete description of the Q(y) absorption and fluorescence spectra of BChl a. Spectral asymmetry persists from 4.5 to 298 K. Time-dependent density-functional theory calculations of the gas-phase absorption and emission spectra obtained using the CAM-B3LYP density functional, curvilinear coordinates, and stretch-bend-torsion scaling factors fitted to data for free-base porphyrin quantitatively predict the observed frequencies of the most-significant vibrational modes as well as the observed absorption∕emission asymmetry. Most other semi-empirical, density-functional, and ab initio computational methods severely overestimate the electron-vibrational coupling and its asymmetry. It is shown that the asymmetry arises primarily through Duschinsky rotation.
The Journal of chemical physics 01/2011; 134(2):024506. · 3.09 Impact Factor
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ABSTRACT: The superatom model for nanoparticle structure is shown to be inadequate for the prediction of the thermodynamic stability of gold nanoparticles. The observed large HOMO-LUMO gaps for stable nanoparticles predicted by this model are, for sulfur-stabilized gold nanoparticles, attributed to covalent interactions of the metal with thiyl adsorbate radicals rather than ionic interactions with thiolate adsorbate ions, as is commonly presumed. In particular, gold adatoms in the stabilizing layer are shown to be of Au(0) nature, subtle but significantly different from the atoms of the gold core owing to the variations in the proportion of gold-gold and gold-sulfur links that form. These interactions explain the success of the superatom model in describing the electronic structure of both known and informatory nanoparticle compositions. Nanoparticle reaction energies are, however, found not to correlate with the completion of superatom shells. Instead, local structural effects are found to dominate the chemistry and in particular the significantly different chemical properties of gold nanoparticle and bulk surfaces. These conclusions are drawn from density-functional-theory calculations for the Au(102)(p-mercaptobenzoic acid)(44) nanoparticle based on the X-ray structure (Jadzinsky, P. D.; et al. Science 2007, 318, 430), as well calculations for the related Au(102)(S(*)-CH(3))(44) nanoparticle, for the inner gold-cluster cores, for partially and overly reacted cores, and for Au(111) surface adsorbates.
Journal of the American Chemical Society 06/2010; 132(24):8378-84. · 9.91 Impact Factor
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ABSTRACT: Penrose and Hameroff have argued that the conventional models of a brain function based on neural networks alone cannot account for human consciousness, claiming that quantum-computation elements are also required. Specifically, in their Orchestrated Objective Reduction (Orch OR) model [R. Penrose and S. R. Hameroff, J. Conscious. Stud. 2, 99 (1995)], it is postulated that microtubules act as quantum processing units, with individual tubulin dimers forming the computational elements. This model requires that the tubulin is able to switch between alternative conformational states in a coherent manner, and that this process be rapid on the physiological time scale. Here, the biological feasibility of the Orch OR proposal is examined in light of recent experimental studies on microtubule assembly and dynamics. It is shown that the tubulins do not possess essential properties required for the Orch OR proposal, as originally proposed, to hold. Further, we consider also recent progress in the understanding of the long-lived coherent motions in biological systems, a feature critical to Orch OR, and show that no reformation of the proposal based on known physical paradigms could lead to quantum computing within microtubules. Hence, the Orch OR model is not a feasible explanation of the origin of consciousness.
Physical Review E 08/2009; 80(2 Pt 1):021912. · 2.26 Impact Factor
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ABSTRACT: Diastereopure (1R,2R)-N,N'-bis(acetylacetone)cyclohexanedi-imine L(1) and its corresponding (1R,2R)L(1)/(1S,2S)L(2) enantiomeric mixture react with AgNO(3) to yield the unusual coordination polymer [Ag(2)(L(1))(L(2))(NO(3))(2)](n) (1) and the unique trimetallic discrete species {[Ag(3)(L(1))(3)(micro(3)-O,O,O-NO(3))(H(2)O)(3)](2)(NO(3))}(NO(3))(3) x 8.5H(2)O (2) which incorporates a symmetrical micro(3)-bridging nitrato group that gives rise to a C(3)-symmetric triskelion motif; both species also feature gamma-carbon eta(1) aryl-like coordination of neutral bridging acetylacetone-imine units to the respective Ag(I) centres.
Dalton Transactions 08/2009; · 3.84 Impact Factor
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ABSTRACT: Self-assembled monolayers (SAMs) formed by chemisorption of a branched-chain alkanethiol, 2-methyl-1-propanethiol, on Au(111) surfaces were studied by in situ scanning tunneling microscopy (STM) under electrochemical potential control and analyzed using extensive density functional theory (DFT) calculations. The SAM forms in the unusual (8 × ×3)-4 superlattice, producing a very complex STM image. Seventy possible structures were considered for the SAM, with the calculated lowest-energy configuration in fact predicting the details of the unusual observed STM image. The most stable structure involves two R-S-Au-S-R adatom-mediated motifs per surface cell, with steric-induced variations in the adsorbate alignment inducing the observed STM image contrasts. Observed pits covering 5.6 (0.5% of the SAM surface are consistent with this structure. These results provide the missing link from the structural motifs observed on surfaces at low coverage and on gold nanoparticles to the observed spectroscopic properties of high-coverage SAMs formed by methanethiol. However, the significant role attributed to intermolecular steric packing effects suggests a lack of generality for the adatom-mediated motif at high coverage.
The Journal of Physical Chemistry C 05/2009; 113:19061-19070. · 4.80 Impact Factor
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ABSTRACT: In 1968, Fröhlich showed that a driven set of oscillators can condense with nearly all of the supplied energy activating the vibrational mode of lowest frequency. This is a remarkable property usually compared with Bose-Einstein condensation, superconductivity, lasing, and other unique phenomena involving macroscopic quantum coherence. However, despite intense research, no unambiguous example has been documented. We determine the most likely experimental signatures of Fröhlich condensation and show that they are significant features remote from the extraordinary properties normally envisaged. Fröhlich condensates are classified into 3 types: weak condensates in which profound effects on chemical kinetics are possible, strong condensates in which an extremely large amount of energy is channeled into 1 vibrational mode, and coherent condensates in which this energy is placed in a single quantum state. Coherent condensates are shown to involve extremely large energies, to not be produced by the Wu-Austin dynamical Hamiltonian that provides the simplest depiction of Fröhlich condensates formed using mechanically supplied energy, and to be extremely fragile. They are inaccessible in a biological environment. Hence the Penrose-Hameroff orchestrated objective-reduction model and related theories for cognitive function that embody coherent Fröhlich condensation as an essential element are untenable. Weak condensates, however, may have profound effects on chemical and enzyme kinetics, and may be produced from biochemical energy or from radio frequency, microwave, or terahertz radiation. Pokorný's observed 8.085-MHz microtubulin resonance is identified as a possible candidate, with microwave reactors (green chemistry) and terahertz medicine appearing as other feasible sources.
Proceedings of the National Academy of Sciences 03/2009; 106(11):4219-24. · 9.68 Impact Factor
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ABSTRACT: The fabrication of porphyrin thin films derived from dichloro[5,10,15,20-tetra(heptyl)porphyrinato]tin(IV) [Cl-Sn(THP)-Cl] in the holes of photonic crystal fibers over 90 cm in length is described. Evanescent field spectroscopy (EFS) is used to investigate the interfacial properties of the films, with the high surface optical intensity and the long path length combining to produce significant absorption. By comparison with results obtained for similar films formed from Cl-Sn(THP)-Cl inside fused-silica cuvettes and on glass slides, the film is shown to be chemisorbed as a surface Si-O-Sn(THP)-X (X = Cl or OH) species. In addition to the usual porphyrin Q and Soret bands, new absorptions in the in-fiber films are observed by EFS at 445 nm and between 660-930 nm. The 660-930 nm band is interpreted as a porphyrin to silicon charge-transfer transition and postulated to arise following chemisorption at mechanical-strain induced defect sites on the silica surface. Such defect sites are caused by the optical fiber production process and are less prevalent on other glass surfaces. EFS within optical fibers therefore offers new ways for understanding interface phenomena such as surface adsorbates on glass. Such understanding will benefit all devices that exploit interface phenomena, both in optical fibers and other integrated waveguide forms. They may be directly exploited to create ultrasensitive molecular detectors and could yield novel photonic devices.
Journal of the American Chemical Society 03/2009; 131(8):2925-33. · 9.91 Impact Factor
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ABSTRACT: The conduction properties of phenanthroline-terminated, polycyclic extended π-conjugated molecular wires are investigated using density functional theory (DFT) in combination with Green's function techniques and group theory. While these molecules could possibly be thought of as accessible graphene-like fragments, they are calculated to conduct poorly. The decay constant for their exponential decrease of conductance with length is in excess of 0.6 Å−1 for the addition of internal fused quinoxaline groups and in excess of 0.9 Å−1 for the addition of internal pyrazine-fused pyrene groups. Furthermore, while the bidentate phenanthroline connectors adhere strongly to gold, they are sometimes predicted to be less conductive than related monodentate connectors. Careful design is thus required for any graphene-like extended π-system intended for single-molecule conduction applications.
Journal of Physics Condensed Matter 06/2008; 20(29):295208. · 2.55 Impact Factor
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Wenbo E,
Karl M Kadish,
Paul J Sintic,
Tony Khoury,
Linda J Govenlock,
Zhongping Ou,
Jianguo Shao,
Kei Ohkubo, Jeffrey R Reimers,
Shunichi Fukuzumi,
Maxwell J Crossley
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ABSTRACT: Through-porphyrin electronic communication is investigated using "linear-type" and "corner-type" bis(quinoxalino)porphyrins in free-base form and their ZnII, CuII, NiII, and PdII derivatives. These compounds are porphyrins with quinoxalines fused on opposite or adjacent beta,beta'-pyrrolic positions; they were synthesized from 5,10,15,20-tetrakis(3,5-di-tert-butylphenyl)-porphyrin-2,3,12,13- and -2,3,7,8-tetraone, respectively, by reaction with 1,2-phenylenediamine. The degree of electron spin delocalization into the fused rings in the pi-radical anions of the free-base and metal(II) bisquinoxalinoporphyrins was elucidated by electrochemistry, UV-vis absorption, and electron spin resonance (ESR) spectra of the singly reduced species and density functional theory calculations. Hyperfine splitting patterns in the ESR spectra of the pi-radical anions show that symmetric molecules have delocalized electron spin, indicating that significant inter-quinoxaline interactions are mediated through the central porphyrin unit, these interactions being sufficient to guarantee through-molecule conduction. However, when molecular symmetry is broken by tautomeric exchange of the inner nitrogen hydrogens in the free-base porphyrin with a corner-type quinoxaline substitution pattern, the pi-radical anion becomes confined so that one quinoxaline group is omitted from spin delocalization. This indicates the appearance of a unidirectional barrier to through-molecule conduction, suggesting a new motif for chemically controlled rectification.
The Journal of Physical Chemistry A 02/2008; 112(3):556-70. · 2.95 Impact Factor
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ABSTRACT: Quinoxalino[2,3-b]porphyrins are pi-expanded porphyrins, having a quinoxaline fused to a beta,beta-pyrrolic position of the porphyrin. They are used as components in systems proposed as molecular wires. Knowledge of their redox properties is of value in the design of electron- or hole-conduction systems. In particular, the location of the charge density in the radical anions of quinoxalinoporphyrins can be modulated by peripheral functionalization. New theoretical treatments of electrochemical potentials are developed that identify the site of reduction in both the anions and the dianions of 33 quinoxalinoporphyrins. These molecules include free-base and metallated macrocycles substituted on the quinoxaline with electron-withdrawing groups (NO2, Cl, Br) and/or electron-donating groups (NH2, OCH3). Spectroelectrochemistry, density-functional theory calculations, and substituent-parameter models are used to verify the analysis. Five distinct patterns are observed for the locations of the first and second reductions; some of these patterns involve delocalized charges. Nitroquinoxalinoporphyrins with the nitro groups at the 5- and 6-quinoxaline positions are found to have quite different properties owing to distortions caused by peri interactions that force the nitro group of the 5-nitro regioisomer out of conjugation. Charge localization on the nitroquinoxaline fragment is found for some molecules, and this is attributed to ion-pairing with the 0.1 M tetrabutylammonium perchlorate electrolyte used, leading to the verified prediction that electron-paramagnetic resonance spectra of these molecules taken without the electrolyte yield delocalized anions. These properties enable the control of conduction through molecular wires synthesised from quinoxalinoporphyrins.
Physical Chemistry Chemical Physics 02/2008; 10(2):268-80. · 3.57 Impact Factor
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ABSTRACT: Since the synthesis of the Creutz-Taube ion, the nature of its charge localization has been of immense scientific interest, this molecule providing a model system for the understanding of the operation of biological photosynthetic and electron-transfer processes. However, recent work has shown that its nature remains an open question. Many systems of this type, including photosynthetic reaction centres, are of current research interest, and thereby the Creutz-Taube ion provides an important chemical paradigm: the key point of interest is the details of how such molecules behave. We lay the groundwork for the construction of a comprehensive model for its chemical and spectroscopic properties. Advances are described in some of the required areas including: simulation of electronic absorption spectra; quantitative depiction of the large interaction of the ion's electronic description with solvent motions; and the physics of Ru-NH3 spectator-mode vibrations. We show that details of the solvent electron-phonon coupling are critical in the interpretation of the spectator-mode vibrations, as these strongly mix with solvent motions when 0.75<2J/lambda<1. In this regime, a double-well potential exists which does not support localized zero-point vibration, and many observed properties of the Creutz-Taube ion are shown to be consistent with the hypothesis that the ion has this character.
Philosophical Transactions of The Royal Society A Mathematical Physical and Engineering Sciences 01/2008; 366(1862):15-31. · 2.77 Impact Factor
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ABSTRACT: The energetics of formation of thiyl-gold self-assembled monolayers is investigated using density-functional theory simulations. It is found that the chemisorption of dimethyl disulfide on the reconstructed Au(111) (22 x radical3) surface is most favored at the fcc reconstruction stripe, with initial physisorption leading to disulfide dissociation, adatom/vacancy-pair formation, and then, at a coverage of 7.8% sulfur atoms per gold atom, surface reconstruction lifting. At higher coverages, monolayer formation proceeds similarly on the unreconstructed surface, leading to surface pitting. Formation of the analogous adatom/vacancy-pair bound dissociated adsorbate complex on exposure of the clean unreconstructed surface to methanethiol is shown to be endothermic, however.
Journal of the American Chemical Society 12/2007; 129(47):14532-3. · 9.91 Impact Factor
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ABSTRACT: A donor-acceptor linked triad with a short spacer (Fc-ZnP-C60) 1 was designed and synthesised to attain the longest charge-separation lifetime, 630 micros, ever reported for triads at room temperature. The ferrocene electron donor and fullerene electron acceptor of triad 1 are attached to imidazole rings fused to opposite beta,beta'-pyrrolic positions of the zinc porphyrin. After excitation of the porphyrin, electron transfer to C60 occurs within 230 ps, followed by hole transfer to ferrocene after 500 ps to produce the long-lived charge-separated state.
Physical Chemistry Chemical Physics 11/2007; 9(38):5260-6. · 3.57 Impact Factor
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ABSTRACT: Scanning tunneling microscopy (STM) images of 1,10-phenanthroline (PHEN) and dipyrido[3,2-a:2‘,3‘-c]phenazine (DPPZ) on Au(111) are recorded using both in situ and ex situ techniques. The images of PHEN depict regimes of physisorption and chemisorption, whereas DPPZ is only physisorbed. All physisorbed structures are not pitted and fluctuate dynamically, involving aligned (4 × 4) surface domains with short-range (ca. 20 molecules) order for PHEN but unaligned chains with medium-range (ca. 100 molecules) order for DPPZ. In contrast, the chemisorbed PHEN monolayers remain stable for days, are associated with surface pitting, and form a (4 × √13)R46° lattice with long-range order. The density of pitted atoms on large gold terraces is shown to match the density of chemisorbed molecules, suggesting that gold adatoms link PHEN to the surface. For PHEN, chemisorbed and physisorbed adsorbate structures are optimized using plane-wave density-functional theory (DFT) calculations for the surface structure. Realistic binding energies are then obtained adding dispersive corrections determined using complete-active-space self-consistent field calculations using second-order perturbation theory (CASPT2) applied to cluster-interaction models. A fine balance between the large adsorbate−adsorbate dispersive forces, adsorbate−surface dispersive forces, gold ligation energy, and surface mining energy is shown to dictate the observed phenomena, leading to high surface mobility and substrate/surface lattice incommensurability. Increasing the magnitude of the dispersive forces through use of DPPZ, rather than PHEN, to disturb this balance produced physisorbed monolayers without pits and/or surface registration but with much longer-range order. Analogies are drawn with similar but poorly understood processes involved in the binding of thiols to Au(111).
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