77 research outputs found
Low-frequency modes in the Raman spectrum of sp-sp2 nanostructured carbon
A novel form of amorphous carbon with sp-sp2 hybridization has been recently
produced by supersonic cluster beam deposition showing the presence in the film
of both polyynic and cumulenic species [L. Ravagnan et al. Phys. Rev. Lett. 98,
216103 (2007)]. Here we present a in situ Raman characterization of the low
frequency vibrational region (400-800 cm-1) of sp-sp2 films at different
temperatures. We report the presence of two peaks at 450 cm-1 and 720 cm-1. The
lower frequency peak shows an evolution with the variation of the sp content
and it can be attributed, with the support of density functional theory (DFT)
simulations, to bending modes of sp linear structures. The peak at 720 cm-1
does not vary with the sp content and it can be attributed to a feature in the
vibrational density of states activated by the disorder of the sp2 phase.Comment: 15 pages, 5 figures, 1 tabl
Charge carrier solvation and large polaron formation on a polymer chain revealed in model ab initio computations
When an excess charge carrier is added to a semiconducting polymer chain, it
is well known that the carrier may self-trap into a polaronic state accompanied
by a bond length adjustment pattern. A different mechanism of self-localization
is the solvation of charge carriers expected to take place when the polymer
chain is immersed in polar media such as common solvents. We use
state-of-the-art ab initio computations in conjunction with the Polarizable
Continuum Model to unequivocally demonstrate solvation-induced self-consistent
charge localization into large-radius one-dimensional (1D) polarons on long
carbon chains with the polyynic structure. Within the framework
used, the solvation results in a much more pronounced charge localization. We
believe this mechanism of polaron formation to be of relevance for various 1D
semiconductors in polar environments
Single-Molecule Conductance of Functionalized Oligoynes: Length Dependence and Junction Evolution
Probing Intermetallic Coupling in Dinuclear N-Heterocyclic Carbene Ruthenium(II) Complexes
Synthesis and reactivity of new heteodinuclear iron/rhenium Cx complexes of the formula (n5-C5Me5)Re(NO)(PPh3)(CC)n(n2-dppe)Fe(n5-C5Me5) ( n = 3, 4): Redox properties and a dicobalt hexacarbonyl adduct
International audienc
Impact of donor-acceptor functionalization on the properties of linearly Ï-conjugated oligomers: establishing quantitative relationships for the substituent and substituent cooperative effect based on quantum chemical calculations
To understand better the impact of donor-acceptor substitution on the properties of linearly Ï-conjugated compounds, we performed a computational study on a series of variably substituted trans-polyacetylenes, polyynes, and polythiophenes. The focus of this work is on how rapidly the impact of a given substituent or a given combination of substituents vanishes along the Ï-conjugated chain. The response of the structural (bond-length alternation, rotational barrier) and molecular properties ((hyper)polarizability, chemical shift) to substitution is analyzed using different protocols, including a superposition model for the evaluation of the cooperative effect of substituents in homo- and heterosubstituted oligomers. With the exception of the (hyper)polarizability, the impact of donor-acceptor substitution is found to vanish following an exponential. The rate of decay of the substituent impact is found to be characteristic for each backbone, whereas the choice of substituent determines the absolute value of the respective property. The combination of substituents is shown to determine whether the substituent cooperative effect on a property is of an enhancing or damping nature. The rate of decay of the cooperative effect on most properties, including the (hyper)polarizability, is also found to follow an exponential law
Probing intermetallic coupling in dinuclear N-heterocyclic carbene ruthenium(II) complexes
A series of bimetallic N-heterocyclic carbene (NHC) ruthenium(II) complexes were synthesized, which comprise two [RuClâ(cymene)(NHC)] units that are interlinked via the NHC nitrogens by alkyl chains of different length. Electrochemical characterization revealed two mutually dependent oxidation processes for the complex with a methylene linker, indicating moderate intramolecular electronic coupling of the two metal centers (class II system). The degree of coupling decreases rapidly upon increasing the number of CHâ units in the linker and provides essentially decoupled class I species when propylene or butylene linkers are used. Electrochemical analyses combined with structural investigations suggest a through-bond electronic coupling. Replacement of the alkyl linker with a p-phenylene group afforded cyclometalated complexes, which were considerably less stable. The electronic coupling in the methylene-linked complex and the relatively robust NHCâruthenium bond may provide access to species that are switchable on the molecular scale
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