No abstract

A family of trialkylsilylethynyl (TAS)-functionalized pentacenes (PENs) and anthradithiophenes (ADTs) are of immense interest due to their good solubility and air stability for uses in optoelectronic devices. Different TAS-substituted PENs and ADTs would result in different crystal packing motifs and carrier transport properties. Quantum nuclear-enabled hopping model combined with molecular dynamics (MD) simulations was used to investigate the effects of the chemical modifications on the carrier transport properties. The disorder-free hole mobilities show that 6,13-bis­(trialkylsilylethynyl)­anthradithiophenes (TAS-ADTs) own better intrinsic hole transport behaviors than 6,13-bis­(trialkylsilylethynyl)­pentacenes (TAS-PENs). The MD simulations show that in comparison with TAS-PENs, the thermal disorder effects are less significant for TAS-ADTs; this is probably due to the C–H···S hydrogen bonds, which are thought to stabilize the molecules in crystal environments. Furthermore, the syn-TAS-ADTs show more serious nonlocal electron–phonon interactions than the anti-TAS-ADTs, which could be ascribed to the larger S···S overlap between neighboring molecules in the syn-TAS-ADTs. Additionally, symmetry-adapted perturbation theory and Hirshfeld surface analyses were performed to characterize the effects of noncovalent interactions on packing motifs. The results indicate that the C–H···π interaction, the balance relationship between electrostatic, induction, dispersion, and exchange repulsion interactions, and the C–H···S hydrogen bonds are responsible for the very different crystal packing motifs between these materials.

The charge transport properties of a series of rubrene derivatives were systematically investigated by density functional theory and molecular dynamics (MD) simulations. It was found that functionalizing electron-withdrawing groups (−CN, −CF3, or fluorination) on the peripheral phenyls not only enhance the chemical stability of materials but also favor electron injection by lowering the energy levels of frontier molecular orbitals and increasing the electron affinities. Derivatives 2–5 and 9, exhibiting packing motifs similar to rubrene but closer π-stacking distances, possess large hole and electron-transfer integrals, significant bandwidths, and small effective masses, suggesting excellent ambipolar semiconductor behavior. The maximum hole­(electron) mobilities in the Marcus hopping mechanism based on kinetic Monte Carlo simulation can reach 14.0–16.5(1.6–3.5) cm2 V–1 s–1. Interestingly, the antiparallel 2-D brick stacking and twisted backbones of fluorinated derivatives 11 and 12 result in nearly 1-D percolation network but balanced hole and electron transport property. In contrast, the parallel 2-D brick stacking of 14 leads to 2-D percolation network. Their maximum hole and electron mobilities fall in the range of 0.5–3.6 and 2.0–4.8 cm2 V–1 s–1. Furthermore, MD simulations show that dynamic disorder is strongly detrimental to the hole transfer but has a little influence on the electron transfer for 1–5. Moreover, severe twist of backbones of 9 leads to almost 1 order of magnitude lowered mobility. In addition, the influences of different substituents on the molecular structure, packing motif, and intermolecular reorganization energy are discussed.

To obtain anthracene-based derivatives with electron transport behavior, two series of anthracene-based derivatives modified by trifluoromethyl groups (−CF3) and cyano groups (−CN) at the 9,10-positions of the anthracene core were studied. Their electronic structures and crystal packings were also analyzed and compared. The charge-carrier mobilities were evaluated by quantum nuclear tunneling theory based on the incoherent charge-hopping model. Our results suggest that introducing −CN groups at 9,10-positions of the anthracene core is more favorable than introducing −CF3 to maintain great planar rigidity of the anthracene skeleton, decreasing more lowest unoccupied molecular orbital energy levels (0.45–0.55 eV), reducing reorganization energies, and especially forming a tight packing motif. Eventually, the excellent electron transport materials could be obtained. The molecule 1-B in Series 1 containing −CF3 groups is an ambipolar organic semiconductor (OSC) material with a 2D transport network, and its value of μh‑max/μe‑max is 1.75/0.47 cm2 V–1 s–1 along different directions; 2-A and 2-C in Series 2 with −CN groups are excellent n-type OSC candidates with the maximum intrinsic mobilities of 3.74 and 2.69 cm2 V–1 s–1 along the π–π stacking direction, respectively. Besides, the Hirshfeld surface and quantum theory of atoms in molecules analyses were applied to reveal the relationship between noncovalent interactions and crystal stacking.

Combining quantum-tunneling-effect-enabled hopping theory with kinetic Monte Carlo simulation and dynamic disorder effects, the charge transport properties of a series of N-hetero 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-PEN) derivatives with halogen substitutions were studied.