Chemistry

Polycyclic aromatic hydrocarbons (PAHs) play a central role in materials science due to their extended π-conjugated systems, with their stability and reactivity depending critically on their aromatic character. In this work, we systematically investigated the aromaticity and stability of a broad range of linear (acenes, phenacenes, biphenylenes, and cyclobuta-acenes) and belt-like (cyclacenes, cyclophenacenes, and cyclobiphenylenes) PAHs containing five to twelve benzene rings. A diverse set of aromaticity descriptors was employed, including geometric (HOMA), electronic (MCI, FLU) and magnetic (NICS) descriptors, plus the recently developed Q₂ indices, based on the components of the distributed multipole analysis (DMA) electric quadrupole tensor. These data were complemented by stability analyses using singlet–triplet energy splitting (ΔE_S–T) and fractional occupation number-weighted densities (N_FOD) values. Our results indicate that acenes and phenacenes follow a comparable aromatic trend, with inner rings possessing lower aromaticity and the edge rings showing a more pronounced aromatic character. A subtle difference is observed in the position of the most aromatic ring, which lies slightly closer to the interior in acenes. Phenacenes, however, exhibit greater overall stability, attributed to their armchair edges. For biphenylenes and cyclobuta-acenes, the antiaromatic cyclobutadiene moiety perturbs the aromaticity only in its direct neighborhood and preserves the aromaticity in the remaining chains. In belt-like systems, cyclacenes exhibit strong radical character and low stability, consistent with longstanding synthetic challenges, whereas cyclophenacenes display enhanced aromaticity and stability with extending size. Cyclobiphenylenes combine localized antiaromatic centers with preserved benzene-like aromaticity in rings distant from the cyclobutadiene unit.

With the growing concern over increased carbon dioxide concentrations in our planet’s atmosphere, much research is being devoted to improving the methods of carbon capture and storage. Amine-based carbon capture techniques are advantageous due to amine’s ability to react directly and reversibly with carbon dioxide to form solid products. To better understand the composition of the solid products obtained by reactions of carbon dioxide with amines under different conditions, such as reactions with gaseous and solid CO₂ (dry ice), spontaneous areal absorbance of CO₂, and others, several such reactions were conducted. Single-crystal X-ray diffraction analysis of the seven previously and newly observed carbamate derivatives was carried out. The synthetic and structural results of solid products have been compared with published data on the same materials obtained by different methods. Peculiarities of hydrogen bonding were described for these materials based on the topological approach.

In this work, we report the one-pot synthesis and characterization of four water-soluble 2-hydroxybenzo[e][1,2]oxaphosphinine 2-oxides. The compounds were obtained by cascade reactions of (2-ethoxyvinyl)phosphonic dichloride with phenol or naphthol derivatives, and their acid–base, structural, and photophysical properties were investigated using a combination of experimental and computational methods. These compounds exhibit UV–vis absorption maxima at 209–341 nm and fluorescence maxima at 300–394 nm. Notably, these cyclic phosphonic acids exhibit unusually strong acidity with pK_a values from −1.3 to 0, comparable to mineral acids; complete protonation is not achieved even in concentrated HCl. The acidity trends and spectra were further analyzed by DFT using both explicit and implicit solvation models.