Virtual Design in Organic Electronics: Screening of a Large Set of 1,4-Bis(phenylethynyl)benzene Derivatives as Molecular Semiconductors

Abstract

In this work, we have theoretically studied the electronic properties of a large series of 1,4bis(phenylethynyl)benzene derivatives, with the chemical formula Y-C≡C-X-C≡C-Y, being X and Y aromatic rings and chosen to act as donor and acceptor moieties. Employing state-of-the-art DFT calculations, we have analyzed a set of relevant electronic properties related to the optoelectronic and semiconductor character of these systems, namely molecular and energy levels, electron affinity, ionization potential, reorganization energy and electronic coupling between neighboring molecules forming dimers, obtained after evaluation of binging energy landscapes. The latter energy magnitude needed to disclose first the favoured intermolecular interactions (i.e. the lowest binding energy) to concomitantly estimate the charge transport rates next. The systematic screening performed allowed us to anticipate the possible use of some of these derivatives as p-type, n-type or even ambipolar organic molecular semiconductors.

Read between the Molecules: Computational Insights into Organic Semiconductors

“…Variation in the electronic couplings between different pairs of neighbor cores (i.e., in different directions) results in the anisotropy of charge mobility in many crystalline organic semiconductors. In cases where the experimental crystal structure is available, it can be used to extract the representative nearest-neighbor dimers, compute their electronic couplings and construct the angular resolution mobility anisotropy curve. − A more sophisticated alternative, often referred to as the multiscale approach, takes into account the entire crystal structure and involves computing electronic and local electron–phonon couplings, running molecular dynamics simulations to access the energetic, configurational and dynamic disorder, and finally performing the diffusive charge dynamics simulation to evaluate the bulk mobility. − In the absence of experimental crystal structures, which is often the case for newly designed systems, the morphology of ordered systems is often approximated by scanning various dimer geometries, generated either manually by systematically varying their structural parameters ,, or in an automatized manner using, for instance, random search algorithms, and constructing two-dimensional maps of their electronic couplings; for disordered systems, molecular dynamics (MD) simulations are often employed to probe the morphologies . However, neither of these methods affords insights beyond the dimer level.…”

Active discovery of organic semiconductors

“…As an equally established descriptor for the bulk charge mobility we employ the intra-molecular (hole) reorganization energy λ h , which measures the cost of accommodating a new charge state after the carrier has moved to the next molecular site. 46 , 47 As molecular properties, both ϵ HOMO and λ h can be determined by efficient first-principles calculations as detailed in Supplementary Note 2 , where the density-functional theory (DFT) B3LYP 48 – 50 level of theory constitutes a well established accuracy standard 27 , 31 , 39 , 40 , 51 , matching experimental data 44 , 52 . We emphasize though that using the lowest-energy gas-phase conformer for the descriptor calculation disregards packing-effects in the molecular crystal 53 – 55 and we further discuss the influence of conformers on descriptor values in Supplementary Note 3 .…”

“…Just as in conventional computational screening, there are numerous possibilities to refine the underlying candidate evaluation through additional (or alternative) descriptors. In the exemplified OSC context, obvious avenues could be to explicitly consider synthetic accessibility 84 , electronic coupling and charge-transport networks in the molecular solid 46 , 51 , 85 , 86 or electron-phonon coupling 87 . In view of the high data efficiency of the AML approach, one may also drop the present focus on computationally least-demanding descriptors, originally dictated by the excessive queries in conventional exhaustive screening work.…”

High-throughput virtual screening for organic electronics: a comparative study of alternative strategies

“…thiophene-, furan-, triazine- and benzene-based compounds with predefined connecting points to construct a set of 10 million unique molecules, including oligomeric sequences with up to five units. M. Moral et al , 353 on the other hand, took a more restricted approach and investigated 100 1,4-bis(phenylethynyl)-benzene derivatives with the formula Y–C C–X–C C–Y. This rigid architecture was used with consideration of the axial rod-like feature, which is prevalent in molecular scale electronics.…”