Bih-Yaw Jin

Generalized Classification Scheme of Toroidal and Helical Carbon Nanotubes

In this study, we develop a generalized classification scheme for toroidal (TCNT) and helical carbon nanotubes (HCNT) containing both pentagons and heptagons simultaneously. We show that a particular class of TCNTs with n-fold rotational symmetry and well-defined latitude coordinates can be uniquely characterized by a set of four indices, and each of the indices can be linked to the relative arrangement of pentagons and heptagons in the corresponding torus. Chiral isomers or the corresponding helical derivatives, HCNTs, can also be readily derived either by introducing a chiral vector or dissecting a distorted TCNT through certain longitude. This generalized scheme can generate the whole family of fullerenes with genus one, ranging from giant TCNTs down to small ones containing only a few hundred atoms. To the best of our knowledge, almost all of the construction methods for TCNTs in the literature belong to special cases of our generalized classification scheme.

Clustered Geometries Exploiting Quantum Coherence Effects for Efficient Energy Transfer in Light Harvesting

Elucidating quantum coherence effects and geometrical factors for efficient energy transfer in photosynthesis has the potential to uncover nonclassical design principles for advanced organic materials. We study energy transfer in a linear light-harvesting model to reveal that dimerized geometries with strong electronic coherences within donor and acceptor pairs exhibit significantly improved efficiency, which is in marked contrast to predictions of the classical Forster theory. We reveal that energy tuning due to coherent delocalization of photoexcitations is mainly responsible for the efficiency optimization. This coherence-assisted energy-tuning mechanism also explains the energetics and chlorophyll arrangements in the widely studied Fenna–Matthews–Olson complex. We argue that a clustered network with rapid energy relaxation among donors and resonant energy transfer from donor to acceptor states provides a basic formula for constructing efficient light-harvesting systems, and the general principles reve...

Energy‐Level Alignment for Single‐Molecule Conductance of Extended Metal‐Atom Chains

The use of single-molecule junctions for various functions constitutes a central goal of molecular electronics. The functional features and the efficiency of electron transport are dictated by the degree of energy-level alignment (ELA), that is, the offset potential between the electrode Fermi level and the frontier molecular orbitals. Examples manifesting ELA are rare owing to experimental challenges and the large energy barriers of typical model compounds. In this work, single-molecule junctions of organometallic compounds with five metal centers joined in a collinear fashion were analyzed. The single-molecule i-V scans could be conducted in a reliable manner, and the EFMO levels were electrochemically accessible. When the electrode Fermi level (EF ) is close to the frontier orbitals (EFMO ) of the bridging molecule, larger conductance was observed. The smaller |EF -EFMO | gap was also derived quantitatively, unambiguously confirming the ELA. The mechanism is described in terms of a two-level model involving co-tunneling and sequential tunneling processes.

An efficient quantum jump method for coherent energy transfer dynamics in photosynthetic systems under the influence of laser fields

We present a non-Markovian quantum jump (NMQJ) approach for simulating coherent energy transfer dynamics in molecular systems in the presence of laser fields. By combining a coherent modified Redfield theory (CMRT) and a NMQJ method, this new approach inherits the broad-range validity from the CMRT and highly efficient propagation from the NMQJ. To implement NMQJ propagation of CMRT, we show that the CMRT master equation can be cast into a generalized Lindblad form. Moreover, we extend the NMQJ approach to treat time-dependent Hamiltonian, enabling the description of excitonic systems under coherent laser fields. As a benchmark of the validity of this new method, we show that the CMRT–NMQJ method accurately describes the energy transfer dynamics in a prototypical photosynthetic complex. Finally, we apply this new approach to simulate the quantum dynamics of a dimer system coherently excited to coupled single-excitation states under the influence of laser fields, which allows us to investigate the interplay between the photoexcitation process and ultrafast energy transfer dynamics in the system. We demonstrate that laser-field parameters significantly affect coherence dynamics of photoexcitations in excitonic systems, which indicates that the photoexcitation process must be explicitly considered in order to properly describe photon-induced dynamics in photosynthetic systems. This work should provide a valuable tool for efficient simulations of coherent control of energy flow in photosynthetic systems and artificial optoelectronic materials.

Charge-Transfer Interactions in Organic Functional Materials

Our goal in this review is three-fold. First, we provide an overview of a number of quantum-chemical methods that can abstract charge-transfer (CT) information on the excited-state species of organic conjugated materials, which can then be exploited for the understanding and design of organic photodiodes and solar cells at the molecular level. We stress that the Composite-Molecule (CM) model is useful for evaluating the electronic excited states and excitonic couplings of the organic molecules in the solid state. We start from a simple polyene dimer as an example to illustrate how interchain separation and chain size affect the intercahin interaction and the role of the charge transfer interaction in the excited state of the polyene dimers. With the basic knowledge from analysis of the polyene system, we then study more practical organic materials such as oligophenylenevinylenes (OPVn), oligothiophenes (OTn), and oligophenylenes (OPn). Finally, we apply this method to address the delocalization pathway (through-bond and/or through-space) in the lowest excited state for cyclophanes by combining the charge-transfer contributions calculated on the cyclophanes and the corresponding hypothetical molecules with tethers removed. This review represents a step forward in the understanding of the nature of the charge-transfer interactions in the excited state of organic functional materials.

Can an entirely negative fluorine in a molecule, viz. perfluorobenzene, interact attractively with the entirely negative site(s) on another molecule(s)? Like liking like!

We present in this study the possibility of the formation of attractive intermolecular interactions between various entirely negative sites localized on a variety of atoms in molecules, leading to the formation of the thirteen isolated dimers examined. Each of these dimers is formed upon the attractive engagement of the totally negatively charged, covalently bound fluorine in perfluorobenzene (C6F6) with similarly charged atoms in each of the nine Lewis bases selected, e.g., water (H2O), ammonia (NH3), hydrogen fluoride (HF), formaldehyde (H2CO), fluoromethane (H3CF), fully fluorinated pyridine (C5F5N), pyrimidine (C4F4N2), pyrazine (C4F4N2), and pyridazine ((CF)4N2). The uncorrected binding energies (varying between −0.45 and −2.56 kJ mol−1 with CCSD(T)/6-311G**//M06-2X/6-311++G(d,p)) and intermolecular contact distances (varying between 2.988 and 3.559 A with M06-2X/6-311++G(d,p)) calculated for these dimers are found to be close to what might be envisaged for any weakly bound dimers, viz., dimers of alkanes and polyhedranes that involve C–H⋯H–C dihydrogen bond contacts with bond dissociation energies in the 0.52–12.38 kJ mol−1 range (Nat. Chem., 2011, 3, 323). The topological charge density results obtained upon the application of quantum theory of atoms in molecules and reduced density gradient noncovalent interaction tools to the static geometries of all the thirteen dimers examined have enabled us to demonstrate that the Oδ−⋯Fδ−, Fδ−⋯Fδ−, and Nδ−⋯Fδ− intermolecular contacts revealed are closed-shell type. The calculated (negative) signs and magnitudes of the electrostatic potentials at various local minima and maxima on the surfaces of the ten monomers examined do not support the above possibilities of attraction between the entirely negative sites, thereby revealing a limitation of the model.

Systematics of High-Genus Fullerenes

In this article, we present a systematic way to classify a family of high-genus fullerenes (HGFs) by decomposing them into two types of necklike structures, which are the negatively curved parts of parent toroidal carbon nanotubes. By replacing the faces of a uniform polyhedron with these necks, an HGF polyhedron corresponding to the vertex configuration of the polyhedron can be obtained. HGF polyhedra including tetrahedron, cube, octahedron, dodecahedron, icosahedron, and truncated icosahedron are proposed under the same construction scheme, which contains nonhexagons other than heptagons. Moreover, simple criteria for determining the stabilities of the proposed HGFs based on four geometric parameters are discussed.

Rational design of polymers for optoelectronic interests

Using organometallic catalysts, two types of polymers containing conjugated moiety and insulating linker are synthesized. The investigations on the photophysical properties of these polymers (photoluminescence, electroluminescence and nonlinear optical properties) are briefly summarized. These polymers represent a new class of materials for optoelectronic interests.

Hexahalogenated and their mixed benzene derivatives as prototypes for the understanding of halogen···halogen intramolecular interactions: New insights from combined DFT, QTAIM-, and RDG-based NCI analyses.

A large number of fully halogenated benzene derivatives containing the fluorine, chlorine, bromine, and iodine atoms have been experimentally synthesized both as single‐ and co‐crystals (e.g., Desiraju et al., Chem. Eur. J. 2006, 12, 2222), yet the natures of the halogen ··· halogen interactions between the vicinal halogens in these compounds within the intramolecular domain are undisclosed. Given a fundamental understanding of these interactions is incredibly important in many areas of chemical, biological, supramolecular, and material sciences, we present here our newly discovered theoretical results that delineate whilst the nature of an F···F interaction in a pair of two adjacent fluorine atoms in either of the hexafluorobenzene and 1,4‐dibromotetrafluorobenzene compounds examined is almost unclear, each of the latter three hexahalogenated benzene derivatives (viz., C6Cl6, C6Br6, and C6I6), and each of the seven of their fully mixed hexahalogenated benzene analogues, are found to be stabilized by means of a number of halogen···halogen interactions, each a form of long‐range attraction within the intramolecular domain. The Molecular Electrostatic Surface Potential model was found to be unsurprisingly unsuitable in unraveling any of the aforesaid attractions between the halogen atoms. However, such interactions successfully enunciated by a set of noncovalent interaction descriptors of geometrical, topological, and electrostatic origins. These latter properties were extracted combining the results of the Density Functional Theory electronic structure calculations with those revealed from Atoms in Molecules, and Reduced Density Gradient charge density‐based topological calculations, and are expounded in detail to formalize the conclusions.

Transport through a mixed-valence molecular transistor in the sequential-tunneling regime: Theoretical insight from the two-site Peierls–Hubbard model

Transport through a mixed-valence system in the sequential-tunneling region is investigated using the master equation method and a simple two-site Peierls-Hubbard model that includes electron-phonon (e-p) coupling, electron hopping, and electron-electron (e-e) repulsion. The characteristics of Coulomb diamonds in the conductance spectra under three regimes are discussed. In the regime of zero e-p coupling, we found that the widths of Coulomb diamonds are dominated by the competition of electron-hopping and Coulomb repulsion. In the regime of weak and intermediate e-p coupling, by virtue of the normal-mode transformation we found that coupling to the symmetric-mode decreases the widths of Coulomb diamonds. In the regime of strong e-p coupling, an analytical expression for the widths of Coulomb diamonds can be derived using the small polaron transformation. The derived formula provides a new way to estimate e-e interactions and e-p couplings experimentally.