Search results for "ELECTRONIC STRUCTURE"

Molecular Tuning of the Magnetic Response in Organic Semiconductors

2017

The tunability of high-mobility organic semi-conductors (OSCs) holds great promise for molecular spintronics. In this study, we show this extreme variability - and therefore potential tunability - of the molecular gyromagnetic coupling ("g-") tensor with respect to the geometric and electronic structure in a much studied class of OSCs. Composed of a structural theme of phenyl- and chalcogenophene (group XVI element containing, five-membered) rings and alkyl functional groups, this class forms the basis of several intensely studied high-mobility polymers and molecular OSCs. We show how in this class the g-tensor shifts, $\Delta g$, are determined by the effective molecular spin-orbit couplin…

Polythiophene S,S dioxides: an investigation on electrochemical doping

2000

Abstract A new strategy for functionalizing oligothiophenes is the transformation of the thienyl sulphurs into the corresponding S,S dioxides, with the effect of lowering the LUMO energy without significantly affecting the HOMO one. From a quinquethiophene S,S dioxide derivative, a polymer (pQTDO) which can be reversibly n-doped at not very negative potentials still maintaining the property of being p-doped at moderate potential values was electrosynthesized. There is, however, a great difference in the ability to store charge of the polymer’s p- and n-doped forms: a great amount of injected negative charge irreversibly modifies the structure of pQTDO.

Controlling the electronic properties of polythiophene through the insertion of nonaromatic thienyl S,S-dioxide units

1999

A new class of thiophene-based polymers characterized by the presence of one nonaromatic thienyl S,S-dioxide moiety (O) to every two, four, and six aromatic thienyl units (T) was prepared from the newly synthesized precursors TOT, TTOTT, and TTTOTTT, and electrochemically characterized. The polymers displayed remarkably greater electron affinities than that of polythiophene and could be reversibly n-doped at moderate potentials, while still maintaining the property of also being p-doped at moderate potential values. All polymers were characterized by good p-doping/undoping cyclability, while at least four aromatic units to every nonaromatic one were needed to ensure good n-doping/undoping c…

Naphthalenediimide Polymers with Finely Tuned In-Chain π-Conjugation: Electronic Structure, Film Microstructure, and Charge Transport Properties

2016

Naphthalenediimide-based random copolymers (PNDI-TVTx) with different π-conjugated dithienylvinylene (TVT) versus π-nonconjugated dithienylethane (TET) unit ratios (x = 100→0%) are investigated. The PNDI-TVTx-transistor electron/hole mobilities are affected differently, a result rationalized by molecular orbital topologies and energies, with hole mobility vanishing but electron mobility decreasing only by ≈2.5 times when going from x = 100% to 40%.

Growth and characterization of GdxHg1−xSe crystals

2008

Abstract The growth of GdxHg1−xSe crystals by the vertical Bridgman method was studied in the composition range 0⩽x⩽0.1. The structural and electronic properties of GdxHg1−xSe crystals were investigated as a function of composition. It was found that an increase in gadolinium content up to x=0.01 results in a decrease of structural defects and an increase in electron mobility up to the maximum value of μ77≈2.8×105 cm2/V s. Structural defects start to increase at x>0.01, and the formation of Gd2Se3 amorphous phase takes place at x>0.03. On the base of the electron-spin resonance investigation, it was shown that the Gd incorporates into the HgSe host in Gd3+ charge state at the concentration …

On the relations between aromaticity and substituent effect

2019

Aromaticity/aromatic and substituent/substituent effects belong to the most commonly used terms in organic chemistry and related fields. The quantitative description of aromaticity is based on energetic, geometric (e.g., HOMA), magnetic (e.g., NICS) and reactivity criteria, as well as the properties of the electronic structure (e.g., FLU). The substituent effect can be described using either traditional Hammett-type substituent constants or characteristics based on quantum-chemistry. For this purpose, the energies of properly designed homodesmotic reactions and electron density distribution are used. In the first case, a descriptor named SESE (energy stabilizing the substituent effect) is o…

Theoretical study of asymmetrically substituted poly(organosilanes)

1994

Summary form only given. Poly(organosilanes) [-SiRR'-] where R and R' represent various alkyl and aryl groups, are the subject of intense scientific and technological interest because of the interesting properties such as, intense near-UV absorption, highly efficient photoluminiscence, non-linear optical properties, these polymers present. In this contribution, we present the electronic structure of some asymmetrically substituted poly(organositanes). We have focused the study on the effect of the tacticity on the electronic structure of the polymer. We have employed ab initio methods to obtain reliable geometrical parameters. The band structure calculations have been performed using the va…

The First sulfur-containing twin-DCNQI-type acceptor

1994

Understanding the Electronic Reorganization along the Nonpolar [3+2] Cycloaddition Reactions of Carbonyl Ylides

2011

[EN] The nonpolar [3+2] cycloaddition (32CA) reaction of the carbonyl ylide (CY) 23 with tetramethylethylene (TME) 24 has been studied with DFT methods at the B3LYP/6-31G* level. This cycloaddition reaction, which has a very low activation energy of 4.7 kcal/mol, takes place through a synchronous transition structure. A topological analysis of the ELF along the 32CA reaction provides a new scope of the electronic structure of CY 23 as a pseudodiradical species offering a sound explanation of the high reactivity of this CY in nonpolar reactions. In addition, this analysis points to the nonparticipation of the oxygen lone pairs in the 32CA reaction. This cycloaddition can be seen as a pseudod…

Electronic structure of polysilanes: influence of substitution and conformation

1993

Abstract The valence effective Hamiltonian (VEH) quantum-chemical approach is used to investigate the electronic properties of polysilane. The valence band structure calculated for this fully saturated polymer is analyzed in terms of orbital contributions and compared to that of the closely related carbon polymer, polyethylene. The effects of alkyl substitution and silicon backbone conformation are studied by elucidating the modifications that these structural changes induce on the electronic valence band structure of all-trans unsubstituted polysilane. The VEH results predict a decrease of the band gap upon alkyl substitution and on going from helical to all-trans conformations.