Effects of Aromatic Trifluoromethylation, Fluorination, and Methylation on Intermolecular π–π Interactions

Marcus theory states that the rate of charge transfer is directly proportional to the amount of intermolecular orbital overlap. Theoretically optimizing the electronic coupling through the orientation and distance which both can increase the frontier orbital overlap between molecules is an attractive route to potentially provide theoretical insight for discovering new high performance semiconductor materials. To investigate how these parameters qualitatively affect charge transfer of model systems, unconstrained dimer optimizations with MP2 and dispersion-corrected DFT methods were used to probe the π–π interactions of methylated, fluorinated, and trifluoromethylated benzene, pyridine, and bipyridine dimers. These systems can serve as simplified models representing weak noncovalent interactions in organic semiconductor materials. Enhanced intermolecular interaction energies, reduced π–π distances, and more favorable cofacial orientations were found with the trifluoromethylated dimers compared to fluorinated and methylated dimers studied. Similar effects were found with donor–acceptor pairs that represent organic p-n heterojunction systems. These enhanced π–π interactions are likely caused by increased molecular quadrupole moment and dispersion interaction associated with trifluoromethylation. This computational study illustrates the strong potential of trifluoromethylation and, possibly perfluoroalkylation of acenes and heteroacenes, leading qualitatively to enhanced electron transfer through better π–π stacked structures, making them viable candidates for use as n-type organic semiconductor materials. The findings also provide insight for fundamental interactions between drug molecules that include fluorinated and trimethylfluorinated aromatics binding to protein receptors

Arene Trifluoromethylation: An Effective Strategy to Obtain Air-Stable n‑Type Organic Semiconductors with Tunable Optoelectronic and Electron Transfer Properties

Modulation of organic semiconductor band gap, electron affinities (EA), ionization potentials (IP), and reorganization energies (λ) associated with charge transfer is critical for its applications. We report here that trifluoromethylation not only increases both IP and EA significantly as expected but also narrows the HOMO–LUMO band gaps and increases considerably the air-stability of arene-based n-type organic semiconductors. The increased air-stability results from relatively high EA energies and a change in oxidation mechanism. Calculated EAs and IPs show that trifluoromethylated arenes are excellent candidates for n-type semiconductor materials; though a moderate increase of inner-sphere reorganization energy (λ_i) associated with charge transfer is the penalty for the improved performance of the trifluoromethylated compounds. However, since λ_i decreases as the π conjugation increases, a rational design to produce air-stable n-type semiconductor materials with reasonably small λ_i is simply to prepare trifluoromethylated arenes with extended π conjugation. Furthermore, we found that structural isomerization can fine-tune the optoelectronic and electronic transfer properties of the corresponding aromatics

Steering Power of Perfluoroalkyl Substituents in Crystal Engineering: Tuning the π–π Distance While Maintaining the Lamellar Packing Motif for Aromatics with Various Sizes of π‑Conjugation

Previously, we reported that introducing perfluoroalkyl substituents onto aromatics promotes the formation of lamellar π–π stacked crystalline materials with short interplanar distances. In this report, we developed a new synthetic route that effectively prepares perfluoroalkylated N-containing aromatics by eliminating a side perfluoroalkylation reaction occurring on nonsubstituted C_sp2–H sites of the corresponding bromoaromatics without regioselectivity. This results in a significant improvement of the yield of target perfluoroalkylated aromatics and facilitates the purification and scale-up processes. X-ray single crystal structural analyses show that lamellar π–π stacked structures with tunable interplanar distances are achieved with fused N-containing aromatics with varying sizes of π-conjugation. Both crystal structures and theoretical calculations demonstrated that the interplanar distance can be fine-tuned with the size of π-conjugation, with larger π-conjugation favoring shorter interplanar distances while still maintaining a lamellar π–π stacked packing motif. Compared to our previous results, we find that simply changing the perfluoroalkyl substituent positions and patterns can change molecular topology to exclusively form lamellar π–π stacked packing motifs through prioritization of specific steric effects. Electrochemical results and absorption spectra confirm that the band gap is reduced due to increasing π-conjugation, and the first reduction potential exhibits a significant positive shift due to both increasing π-conjugation and perfluoroalkylation

Rational Design of Lamellar π–π Stacked Organic Crystalline Materials with Short Interplanar Distance

Organic crystalline materials having a lamellar π–π stacked structural motif with short interplanar distance are significant for many applications. By asymmetrically introducing perfluoroalkyl substituents onto and polarizable sulfur atoms into N-containing heteroaromatics, we successfully synthesized a novel type of aromatic material that preferentially forms lamellar π–π stacked crystalline materials with a interplanar π–π distance of 3.247 Å, more than 0.1 Å shorter than that of highly oriented pyrolytic graphite (HOPG) where interplanar distance ranges from 3.35 to 3.39 Å

The Early Devonian Xitun Vertebrate Fauna in South China inhabited a shallow marine environment with changing salinity

Supplementary table B

Rational Design of Lamellar π–π Stacked Organic Crystalline Materials with Short Interplanar Distance

Organic crystalline materials having a lamellar π–π stacked structural motif with short interplanar distance are significant for many applications. By asymmetrically introducing perfluoroalkyl substituents onto and polarizable sulfur atoms into N-containing heteroaromatics, we successfully synthesized a novel type of aromatic material that preferentially forms lamellar π–π stacked crystalline materials with a interplanar π–π distance of 3.247 Å, more than 0.1 Å shorter than that of highly oriented pyrolytic graphite (HOPG) where interplanar distance ranges from 3.35 to 3.39 Å

Perfluoroalkylation of Square-Planar Transition Metal Complexes: A Strategy To Assemble Them into Solid State Materials with a π–π Stacked Lamellar Structure

Formation of π–π stacked lamellar structure is important for high performance organic semiconductor materials. We previously demonstrated that perfluoroalkylation of aromatics and heteroaromatics was one of the strategies to design organic crystalline materials with π–π stacked lamellar structures while improving air stability as a result of the strong electron withdrawing ability of perfluoroalkyl substituents. Square-planar transition metal complexes with large π-conjugated ligands are also an important category of semiconductor materials. We have perfluoroalkylated square-planar transition metal complexes, leading to the formation of a π–π stacked lamellar crystal packing motif in the solid state. Here we report six crystal structures of Pd and Pt complexes with bis-perfluorobutylated catechol ligand as one of the two ligands that bonds to the metal centers. This structural design possesses similar molecular topology when compared to perfluoroalkylated aromatics and heteroaromatics we have reported previously, again, demonstrating the steering power of the perfluoroalkyl substituents in engineering organic and organometallic solid state materials

The Early Devonian Xitun Vertebrate Fauna in South China inhabited a shallow marine environment with changing salinity

Supplementary table A

The Early Devonian Xitun Vertebrate Fauna in South China inhabited a shallow marine environment with changing salinity

Supplementary table C

BFG&MSF-net: boundary feature guidance and multi-scale fusion network for thyroid nodule segmentation

Accurately segmenting thyroid nodules in ultrasound images is crucial for computer-aided diagnosis. Despite the success of Convolutional Neural Networks (CNNs) and Transformers in natural images processing, they struggle with precise boundaries and small-object segmentation in ultrasound images. To address this, a novel BFG&MSF-Net model is proposed in this paper, utilizing four newly designed modules: (1) a Boundary Feature Guidance Module (BFGM) for improving the edge details capturing; (2) a Multi-Scale Perception Fusion Module (MSPFM) for enhancing the information capture by combining a novel Positional Blended Attention (PBA) with the Pyramid Squeeze Attention (PSA); (3) a Depthwise Separable Atrous Spatial Pyramid Pooling Module (DSASPPM), used in the bottleneck to improve the contextual information capturing; and (4) a Refinement Module (RM) optimizing the low-level features for better organ and boundary identification. Evaluated on the TN3K and DDTI open-access datasets, BFG&MSF-Net demonstrates effective reduction of boundary segmentation errors and superior segmentation performance compared to commonly used segmentation models and state-of-the-art models, which makes it a promising solution for accurate thyroid nodule segmentation in ultrasound images.</p