The title compound, C₁₆H₁₁N₂OF, is a member of the azo dye family. The dihedral angle subtended by the benzene ring and the naphthalene ring system measures 18.75 (7)°, indicating that the compound is not perfectly planar. An intramolecular N—H...O hydrogen bond occurs between the imino and carbonyl groups. In the crystal, the molecules are linked into inversion dimers by C—H...O interactions. Aromatic π–π stacking between the naphthalene ring systems lead to the formation of chains along [001]. A Hirshfeld surface analysis was undertaken to investigate and quantify the intermolecular interactions. In addition, energy frameworks were used to examine the cooperative effect of these intermolecular interactions across the crystal, showing dispersion energy to be the most influential factor in the crystal organization of the compound.

Eleven novel asymmetric pyrimidine derivatives were synthesized. The pyrimidine core was functionalized with a coumarin chromophore and a pro-mesogenic fragment bearing either chiral or linear alkyl chains of variable length and substitution patterns. The thermal properties were investigated using polarized optical microscopy, differential scanning calorimetry, and small-angle X-ray scattering, revealing that only selected derivatives exhibited liquid crystalline phases with ordered columnar or smectic organizations. Linear and nonlinear optical properties were characterized by UV–Vis absorption, fluorescence spectroscopy, two-photon absorption, and second-harmonic generation. Optical responses were found to be highly sensitive to the substitution pattern: derivatives functionalized at the 4 and 3,4,5 positions exhibited enhanced 2PA cross-sections and pronounced SHG signals, whereas variations in alkyl chain length exerted only a minor influence. Notably, compounds forming highly ordered non-centrosymmetric mesophases produced robust SHG-active thin films. Importantly, strong SHG responses were obtained without the need for a chiral center, as the inherent asymmetry of the linear alkyl chain derivatives was sufficient to drive self-organization into non-centrosymmetric materials. These results demonstrate that asymmetric pyrimidine-based architectures combining π-conjugation and controlled supramolecular organization are promising candidates for nonlinear optical applications such as photonic devices, multiphoton imaging, and optical data storage.

Cyclic 1,2-diselenides are known to exhibit three σ-holes around the Se atoms—two in the prolongation of the Se–Se bond and one merging the two electron-depleted areas in the prolongation of the C–Se bonds. Among them, naphthalene peri-diselenides were recently isolated in their radical cation form with halometallates, affording 1:1 salts, where charge activation upon oxidation leads to strong Se•••Cl/Br chalcogen bond (ChB) interactions. Acenaphthene peri-diselenide (1) is shown here to be readily oxidized to its cation radical, showing various association modes of the 1^+• species in the solid state. When engaged in electrocrystallization experiments with (Bu₄N)(FeCl₄), acenaphthene peri-diselenide (1) afforded two salts of the radical cation, formulated as (1)₂(Fe₂Cl₆O) and (1)(FeCl₄), depending on the electrocrystallization conditions. In both salts, short and highly directional Se•••Cl chalcogen bond (ChB) interactions take place, simultaneously involving all three σ-holes surrounding the diselenide bridge, with the reduction ratio (relative to the van der Waals Se•••Cl contact distance of 1.90 + 1.75 = 3.65 Å) reduced to 0.89. In addition, while cation radicals in (1)₂(Fe₂Cl₆O) adopt head-to-tail alternated stacks without any intermolecular Se•••Se contacts, they organize in (1)FeCl₄ into twisted-cofacial dimers, with an intra-dimer Se•••Se contact as short as 3.197(2) Å, i.e., a reduction ratio of 0.84. Such structural organization is reminiscent of those observed in dithiadiazolyl/diselenadiazolyl radicals, which associate into dimers, most often in a cis-cofacial geometry. Here, the 1^+• radicals adopt either a head-to-tail (trans-cofacial) geometry (in the Fe₂Cl₆O²⁻ salt) or a distorted twisted-cofacial geometry (in the FeCl₄⁻ salt), further stabilized by the chelating FeCl₄⁻.