Intermolecular Charge Transfer between Heterocyclic Oligomers. Effects of Heteroatom and Molecular Packing on Hopping Transport in Organic Semiconductors

Abstract

For electron or hole transfer between neighboring conducting polymer strands or oligomers, the intrinsic charge-transfer rate is dictated by the charge-resonance integral and by the reorganization energy due to geometric relaxation. To explain conduction anisotropy and other solid-state effects, a multivariate, systematic analysis of bandwidth as a function of intermolecular orientations is undertaken for a series of oligoheterocycles, using first-principles methods. While cofacial oligomers show the greatest bandwidths at a given intermolecular C-C contact distance, for a fixed center-to-center intermolecular distance, tilted pi-stacking increases pi-overlap (particularly for LUMO orbitals) and decreases electrostatic repulsion, yielding optimum tilt angles for packing of approximately 40-60 degrees at small intermolecular separations. The calculations also reveal that bandwidths and intrinsic mobilities of holes and electrons in conjugated oligoheterocycles can be quite comparable.

Optoelectronic and Semiconducting Properties of Conjugated Polymers Composed of Thiazolo[5,4-d]thiazole and Arene Imides Linked by Ethynylene Bridges

“…70 The electronic coupling strongly depends on the relative arrangement of the molecules in the crystal, with the main electron-hopping pathway found along the π-stacking direction, whereas the electronic coupling between coplanar chains can be generally considered negligible. 4,22,33 For two perfectly stacked molecules, it is known that small molecular displacements may also lead to significant changes in the t 12 value. 45 Figure 7 shows indeed strong oscillations in the value of t 12 for displacements of polymer chains I and V along the x-and y-axes in dimers consisting of two π-stacked infinite chains.…”

“…2,3 The use of organic semiconductors in organic light-emitting diodes (OLEDs), organic solar cells (OSCs), organic thin-film transistors (OTFTs), which in turn can be used for medical and chemical sensing, and organic electrochromic devices as smart-windows and electrochromic mirrors currently attracts a great interest worldwide. [1][2][3][4] The organic materials employed in electronic devices are generally divided into two groups: small molecules (or oligomers) and polymers, which shows different advantages or disadvantages in terms of processability and device performance. In general, higher mobilities have been reported for electronic devices fabricated with semiconductors of moderate size than for those fabricated with polymers.…”

“…4,35 RESULTS AND DISCUSSION Polymer crystal structure. As stated before, the crystal structures of the polymers were modelled using as starting point the spatial arrangements of two stacked periodic chains where their binding energy displays the lowest value.…”

Hydrogenation of Fullerene C60: Material Design of Organic Semiconductors by Computation

“…Up till now, much effort has been made to understand theoretically the relationship between the structure and the carrier-transport properties of these materials [7][8][9][10]. Theoretical investigations can give reliable guidelines for the development of such new organic semiconductors.…”

Theoretical study of the effects of different substituents of tetrathiafulvalene derivatives on charge transport

“…The KT approximation is reliable when the diabatic energies of the donor and acceptor states are the same (i.e., in a symmetric dimer, or more generally, in the transition state structure). Otherwise, KT approximation can overestimate the transfer integral considerably when the molecules are not equal in symmetry [8,30].…”