Chromic properties of dibenzo[j,l]fluoranthenes exhibiting different resonance contributions.

Chromic molecules change colour in response to external stimuli and are utilized in applications such as food additive detection, light dimmers, and biological probes. One of the common design strategies for organic chromic molecules is based on changes in the π-conjugation. We have hypothesized that non-alternant polyaromatic hydrocarbon (PAH) skeletons can be used as backbones for chromic molecules. Herein, we synthesized hydroxy-substituted dibenzo[j,l]fluoranthenes, a class of non-alternant PAHs, as novel chromic compounds and evaluated their halochromic properties by UV-vis and fluorescence spectroscopy. Under basic conditions, the 1-hydroxy derivatives show a hyperchromic shift, whereas the 9-hydroxy derivatives show a bathochromic shift and fluorescence although the skeleton of the chromophore is the same. Density functional theory calculations indicated that the different chromic properties are attributed to the differences in their resonance structures.

Synthesis of mesoionic triazolones via a formal [3+2] cycloaddition between 4-phenyl-1,2,4-triazoline-3,5-dione and alkynes.

1,2,4-Triazoline-3,5-diones (TADs) are versatile reagents and have found widespread adoption in chemical science. Despite their remarkable reactivity toward a wide array of unsaturated hydrocarbons, the chemical reaction between TADs and alkynes has remained largely unexplored. Herein, we demonstrate that 1,1,1,3,3,3-hexafluoro-2-propanol facilitates the unusual [3+2] cycloaddition between 4-phenyl-1,2,4-triazoline-3,5-dione and alkynes, resulting in the formation of unprecedented mesoionic triazolones. Moreover, the structural properties of the resulting triazolone have been investigated by employing X-ray diffraction analysis and Density Functional Theory (DFT) calculations.