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.

Recent advances in the synthesis and applications of fluoranthenes

As an important subclass of polycyclic aromatic hydrocarbons (PAHs), fluoranthenes continue to attract significant attention in synthetic organic chemistry and materials science. In this article, an overview of recent advances in the synthesis of fluoranthene derivatives along with selected applications is provided. First, methods for fluoranthene synthesis with a classification based on strategic bond disconnections are discussed. Then, the total syntheses of natural products featuring the benzo[j]fluoranthene skeleton are covered. Finally, examples of important applications of a variety of fluoranthenes are summarized.

Isolation and characterisation of a stable 2-azaphenalenyl azomethine ylide

Although azomethine ylides have been fully exploited as versatile reactive intermediates in dipolar cycloaddition reactions to construct a variety of heterocyclic compounds involving a nitrogen atom, little is known about their structural and electronic properties. Here a method is developed for the preparation, isolation and characterization of a stable 2-azaphenalenyl based azomethine ylide. N-Phenyl-5,8-di-t-butyl-2-azaphenalenyl cannot be isolated because it undergoes rapid dimerization by C–C bond formation at the 1 and 3 positions. In contrast, sterically bulkier N-2,6-di(isopropyl)phenyl-5,8-di-t-butyl-2-azaphenalenyl can be generated and isolated as deep green crystals under deoxygenated conditions. X-ray crystal analysis of this stable azomethine ylide reveals that its azaphenalenyl skeleton has very small bond alternation and structural deformation. The results of spectroscopic and electrochemical theoretical studies indicate that N-2,6-di(isopropyl)phenyl-5,8-di-t-butyl-2-azaphenalenyl has electronic features that are similar to those of phenalenyl anion and it possesses an extremely high HOMO energy.

Synthesis of π-Extended Fluoranthenes via a KHMDS-Promoted Anionic-Radical Reaction Cascade

An unprecedented KHMDS-promoted domino reaction to furnish hydroxyfluoranthenes is described. Biaryl compounds bearing acyl and naphthylalkenyl moieties are transformed into 9-hydroxydibenzo[j,l]fluoranthenes in a single step through the formation of an aromatic and a pentagonal ring system. A variety of fluoranthenes including those with extended π-conjugation, a heteroaromatic ring, and unsymmetrical substituents could be synthesized. Mechanistic studies reveal a unique reaction cascade where KHMDS acts as both a base and a single-electron donor.

A new fluorophore displaying remarkable solvatofluorochromism and solid-state light emission, and serving as a turn-on fluorescent sensor for cyanide ions

A new fluorophore displays remarkable solvatofluorochromism, a CIEE effect, and an intense blue-green fluorescence in the presence of cyanide ions.