Bipolaron

About: Bipolaron is a research topic. Over the lifetime, 1335 publications have been published within this topic receiving 29154 citations. The topic is also known as: bipolarons.

3D wavelet treatment of solvated bipolaron and polaron

Abstract: Three-dimensional discrete tensor wavelets are applied to calculate wave functions of excess electrons solvated in polar liquids. Starting from the Hartree–Fock approximation for the electron wave functions and from the linear response to the solute charge for the solvent, we have derived the approximate free energy functional for the excess electrons. The orthogonal Coifman basis set is used to minimize the free energy functional and to approximate the electron wave functions. The scheme is applied to the calculation of the properties of the solvated electron and the singlet bipolaron formation. The obtained results indicate that the proposed algorithm is fast and rather efficient for calculating the electronic structure of the solvated molecular solutes.

Conductive, Magnetic, and Optical Properties of Sterically Hindered Dodecithiophenes. Evidence for the Coexistence of Bipolaron and π-Dimer

Abstract: Conductive, magnetic, and optical properties of sterically hindered dodecithiophenes bearing bulky 2,2-bis(butoxy-methyl)-1,3-propanediyl groups were examined. At high doping with FeCl 3 , a completely hindered dodecithiophene had only a poor conductivity of 5 x 10 -4 S cm -1 , but two partially hindered dodecithiophenes had relatively high conductivities of 1.9 and 0.6 S cm -1 , which are one or two orders lower than the conductivity (38 S cm -1 ) of the unhindered dodecithiophene. Despite having different structures and conductivities, all of the doped solids of these dodecithiophenes were magnetically inactive and demonstrated similar optical absorption spectra in the near infrared region, as generally observed for polythiophenes. On the other hand, their optical spectra in dichloromethane were quite different from one another. A solution spectrum of the unhindered dodecithiophene under high doping was characterized by two absorption transitions assignable to a π-dimer. On the other hand, a solution spectrum of the completely hindered dodecithiophene was characterized by an absorption transition due to a bipolaron. Furthermore, the solution spectra of two partially hindered dodecithiophenes could be explained as an overlap of both π-dimeric and bipolaronic bands. From these results, both π-dimer and bipolaron species appear to serve as active charge carriers in conductive poly(oligo)thiophenes.

Formation of large bipolarons

Abstract: An electron in a polar crystal lattice interacting with the longitudinal optical phonon modes is called a polaron. Since the effective electron-phonon interaction is attractive, it enhances the electron’s effective mass. If a second electron in the phonon bath is taken into account, its interaction with the phonons might overcome the electron-electron repulsion. If so, the pair of electrons forms a stable bound state, called bipolaron. Due to the competition between the opposite forces the bipolaron exists only in a small region of electron-phonon coupling constant and electron-electron repulsion. It is the aim to contribute to the investigation of this stability region.

Continuum model for vibrational excitations of conjugated polymers.

Abstract: The continuum model of the coupled electron-phonon system in conjugated polymers is extended to include the lattice kinetic energy and the coupling of several structural degrees of freedom. The model is used to study defect vibrational spectra for a variety of defects that may occur, e.g., solitons, polarons, and bipolarons, in conjugated polymer systems. In agreement with previous theoretical studies of polyacetylene, a class of infrared-active modes common to all mobile bond-alternation defects is obtained. In addition the study reveals a new class of bound vibrations localized at the defect center of a polaron or a bipolaron. These additional infrared-active modes can be used spectroscopically to identify defect types in conjugated polymers such as polyacetylene or polythiophene. Examples considered include doping and photoinduced defects (solitons and polarons) in both (CH${)}_{\mathrm{x}}$ and (CD${)}_{\mathrm{x}}$ as well as photoinduced defects (bipolarons) in polythiophene.

Polarons and bipolarons in polythiophene in the presence of magnetic field

Abstract: Spin degeneracy in conjugated polymers will be destroyed in the presence of magnetic field because of the existence of Zeeman splitting. The characteristic of carriers in polythiophene is studied in the framework of a tight binding model. It is found that spin polarons can be created preferentially in energy when electrons are doped under a reasonable magnetic field considering the influence of electron–electron interactions and electron–phonon coupling, which is favorable for spin polarized transport in organic semiconductors and is of great importance in the field of organic spintronics.