Azulene-Based Organic Functional Materials

Azulene, a nonalternant bicyclic aromatic hydrocarbon distinguished by its fused five- and seven-membered rings and vivid blue hue, has emerged as a versatile scaffold for organic functional materials. Its intrinsic dipole moment and unique electronic distribution underpin a spectrum of applications ranging from optoelectronic devices to chemical sensors and bioimaging probes. Synthetic strategies exploit electrophilic substitution, Brønsted acid-catalysed cyclizations and transition-metal-mediated cross-couplings to access diverse azulene derivatives, including heterocycle-fused frameworks and donor–acceptor architectures. These compounds frequently exhibit low band-gap behaviour, near-infrared absorption and switchable fluorescence upon protonation or redox events. Conjugated azulene-embedded polycyclic aromatic hydrocarbons demonstrate promising charge-transport characteristics, while tailored azulene dyes enhance two-photon microscopy and colourimetric sensing of reactive species. Together, these developments highlight azulene’s global significance as a building block for next-generation organic electronics, photonics and biomedical tools.

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Azulene-Based Organic Functional Materials publication trend

The graph below shows the total number of articles in azulene-based organic functional materials across all publications each year (not limited to Nature Index journals).

Technical terms

Azulene: A 10-π-electron nonalternant bicyclic aromatic hydrocarbon comprising fused five- and seven-membered rings, noted for its blue colour and substantial dipole moment.

Nonalternant aromatic hydrocarbon: An aromatic system in which the arrangement of single and double bonds does not follow the alternancy rule, yielding distinctive electronic properties.

Scholl oxidation: An oxidative cyclodehydrogenation process that fuses adjacent aromatic rings, typically employing Lewis acids or oxidants to build extended polycyclic structures.

Two-photon fluorescence microscopy: An imaging technique based on the near-simultaneous absorption of two photons to excite fluorophores, allowing deep-tissue visualisation with reduced photodamage.

Donor–acceptor architecture: A molecular design combining electron-rich (donor) and electron-deficient (acceptor) units in conjugation to tune optical and electronic characteristics.

References

1. Synthesis of Azuleno[2,1-b]quinolones and Quinolines via Brønsted Acid-Catalyzed Cyclization of 2-Arylaminoazulenes. Molecules (2023).
2. 1,2,3-Triarylazulenes as precursors of azulene-embedded polycyclic aromatic hydrocarbons. Organic Chemistry Frontiers (2024).
3. Azulene-Derived Fluorescent Probe for Bioimaging: Detection of Reactive Oxygen and Nitrogen Species by Two-Photon Microscopy. Journal of the American Chemical Society (2019).