Alternating phenylene and furan/pyrrole/thiophene units-based oligomers: A computational study of the structures and optoelectronic properties

An Informatics Approach for Designing Conducting Polymers

Doping conjugated polymers, which are potential candidates for the next generation of organic electronics, is an effective strategy for manipulating their electrical conductivity. However, selecting a suitable polymer-dopant combination is exceptionally challenging because of the vastness of the chemical, configurational, and morphological spaces one needs to search. In this work, high-performance surrogate models, trained on available experimentally measured data, are developed to predict the p-type electrical conductivity and are used to screen a large candidate hypothetical data set of more than 800 000 polymer-dopant combinations. Promising candidates are identified for synthesis and device fabrication. Additionally, new design guidelines are extracted that verify and extend knowledge on important molecular fragments that correlate to high conductivity. Conductivity prediction models are also deployed at www.polymergenome.org for broader open-access community use.

Torsional Profiles of Thiophene and Furan Oligomers: Probing the Effects of Heterogeneity and Chain Length

A systematic analysis of the torsional profiles of 55 unique oligomers composed of two to four thiophene and/or furan rings (n = 2 to 4) has been conducted using three density functional theory (DFT) methods along with MP2 and three different coupled-cluster methods. Two planar or quasi-planar minima were identified for each n = 2 oligomer system. In every case, the torsional angle (τ) between the heteroatoms about the carbon-carbon bond connecting the two rings is at or near 180° for the global minimum and 0° for the local minimum, referred to as anti and syn conformations, respectively. These oligomers have rotational barrier heights ranging from ca. 2 kcal mol^-1 for 2,2'-bithiophene to 4 kcal mol^-1 for 2,2'-bifuran, based on electronic energies computed near the CCSD(T) complete basis set (CBS) limit. The corresponding rotational barrier for the heterogeneous 2-(2-thienyl)furan counterpart falls approximately halfway between those values. The energy differences between the minima are approximately 2 and 0.4 kcal mol^-1 for the homogeneous 2,2'-bifuran and 2,2'-bithiophene, respectively, whereas the energy difference between the planar local and global minima (at τ = 0 and 180°, respectively) is only 0.3 kcal mol^-1 for 2-(2-thienyl)furan. Extending these three oligomers by adding one or two additional thiophene and/or furan rings resulted in only minor changes to the torsional profiles when rotating around the same carbon-carbon bond as the two-ring profiles. Relative energy differences between the syn and anti conformations were changed by no more than 0.4 kcal mol^-1 for the corresponding n = 3 and 4 oligomers, while the rotational barrier height increased by no more than 0.8 kcal mol^-1.

Assessing the Performance of DFT Functionals for Excited-State Properties of Pyridine-Thiophene Oligomers

In this article, we have examined the accuracy of various density functional theory (DFT) functionals to reproduce the absorption and CD spectra of pyridine-thiophene oligomers. The performance of different levels of approximations in DFT functionals is discussed with reference to the ADC(2) results. Starting from a linear system, like monomer, calculations are carried out at ADC(2) and DFT levels till a helical system, like pentamer, is formed. For vertical excitation energies, results obtained with functionals, like CAM-B3LYP, ωB97XD, and M06-2X, are closer to the ADC(2) results. However, analysis of excited-state properties shows that the state ordering patterns or results regarding natural transition orbitals from these DFT functionals sometimes differ from the ADC(2) results. Global hybrid functionals like B3LYP and PBE0 produce excitation energies which are far away from the ADC(2) benchmark results. Similarly, pure functionals and their long-range corrected versions produce either redshifted or blueshifted energies. For the CD spectra, the above three mentioned functionals, CAM-B3LYP, ωB97XD, and M06-2X, again produce spectra closer to the benchmark spectra.