Periphery Fusion Strategy of a Carbazole-Based Macrocycle toward Coplanar N-Heterocycloarene for High-Mobility Single-Crystal Transistors

Facile Synthesis of Donor-Acceptor Heterocycloarenes Based on Pyrazine Derivatives Possessing Intriguing Iodide Ion Capture Properties

Donor-acceptor (D-A) conjugated systems have been extensively investigated and play important roles in organic electronics. Incorporating D-A structures into (hetero)cycloarenes endows them tunable electronic properties, while the well-defined cavity remains. However, the synthetic complexity of introducing electron-acceptor moieties into (hetero)cycloarenes limits their development and applications. In this paper, the first family of electronically tunable D-A heterocycloarenes (DAHCn, n = 1-5) based on pyrazine derivatives was facilely synthesized through cyclocondensation reaction from a tetraketone-functionalized heterocycloarene precursor prepared using the ketal-protection strategy. The effect of expanded conjugation and the inserted electron-withdrawing group on the electronic structures of the D-A heterocycloarenes was studied systematically by X-ray crystallographic analysis, various spectroscopic measurements, and theoretical calculations. Interestingly, the presence of an electron-withdrawing group polarizes the inner C(sp2)-H and significantly increases the binding affinities of D-A heterocycloarenes to the iodide anion. Meanwhile, the anion affinity can be further modulated by the type of attached substituents and the distance of polarization. More importantly, the dicyanopyrazine derivative DAHC3 shows the highest binding strength to the iodide ion as a 2:1 sandwich complex (log β2 = 12.3 and ΔG = -69.1 kJ mol-1), which is the strongest iodide receptor using C(sp2)-H hydrogen bonding interactions reported to date. Our finding provides a new strategy to design and synthesize D-A heterocycloarenes and strong anion receptors.

The anti-correlation effect of alkyl chain size on the photovoltaic performance of centrally extended non-fullerene acceptors

Contrary to previous results, a unique anti-correlation effect of the alkyl chain size on the photovoltaic performance of acceptors was observed. For a centrally-extended acceptor, replacing linear alkyl chains (n-undecyl for CH-BBQ) on the thienothiophene unit with branched ones (2-butyloctyl for CH-BO) leads to a plunge in the power conversion efficiency of organic solar cells (18.12% vs. 11.34% for binary devices), while the largely shortened ones (n-heptyl for CH-HP) bring a surge in performance (18.74%/19.44% for binary/ternary devices). Compared with CH-BO, the more compact intermolecular packing of CH-HP facilitates carrier transport. The characterization of organic field effect transistors and carrier dynamics also echoes the above results. Molecular dynamics simulations indicate that the encounter of the branched alkyl chains and the extended central core hinders the effective interfacial interaction of polymer donors and acceptors, thus deteriorating the device performance. This work suggests that the conventional strategy for alkyl chain engineering of Y-series acceptors might need to be reconsidered in other molecular systems.

Bowl-Shaped Kekulene Analogues: Cycloarenes with two Five-Membered Rings

Kekulene, a cycloarene composed of 12 fused benzene rings in a circular arrangement, exhibits a highly planar and robust structure. Kekulene has been the subject of investigation into its aromaticity and electronic structure, particularly in relation to the cyclic benzenoid. We have successfully synthesized novel bowl-shaped kekulene analogues with five-membered rings incorporated into the kekulene structure. The results of DFT calculations and VT-NMR spectra indicate that inversion of their concave-convex structures occurs at room temperature. The NICS and AICD plots predict that the Clar's type resonance structure is found in a manner analogous to the pristine kekulene, albeit with the interruption of the π-conjugation on the sp3 carbons at the five-membered rings. Despite the presence of the Clar's resonance structure, the Diels-Alder reaction proceeded smoothly with a dienophile, in contrast to the behavior of planar kekulene derivatives. This study will lead to the creation of novel bowl-shaped compounds and development of reactivity in aromatic compounds.

Molecular Engineering of Rylene Diimides via Sila-Annulation Toward High-Mobility Organic Semiconductors

The continuous innovation of captivating new organic semiconducting materials remains pivotal in the development of high-performance organic electronic devices. Herein, a molecular engineering by combining sila-annulation with the vertical extension of rylene diimides (RDIs) toward high-mobility organic semiconductors is presented. The unilateral and bilateral sila-annulated quaterrylene diimides (Si-QDI and 2Si-QDI) are designed and synthesized. In particular, the symmetrical bilateral 2Si-QDI exhibits a compact, 1D slipped π-π stacking arrangement through the synergistic combination of a sizable π-conjugated core and intercalating alkyl chains. Combining the appreciable elevated HOMO levels and reduced energy gaps, the single-crystalline organic field-effect transistors (SC-OFETs) based on 2Si-QDI demonstrate exceptional ambipolar transport characteristics with an impressive hole mobility of 3.0 cm2 V-1 s-1 and an electron mobility of 0.03 cm2 V-1 s-1 , representing the best ampibolar SC-OFETs based on RDIs. Detailed theoretical calculations rationalize that the larger transfer integral along the π-π stacking direction is responsible for the achievement of the superior charge transport. This study showcases the remarkable potential of sila-annulation in optimizing carrier transport performances of polycyclic aromatic hydrocarbons (PAHs).