Application of Azulene in Constructing Organic Optoelectronic Materials: New Tricks for an Old Dog.

Azulene, as an isomer of naphthalene, has received increasing interest due to its unique chemical structure and unusual photophysical properties, including a large dipole moment of 1.08 D, a narrow energy gap between the HOMO and LUMO, and abnormal fluorescence (anti-Kasha's rule) from the second excited state to the ground state. In this Minireview, the general strategies and representative synthetic methods for the preparation and functionalization of azulene and its derivatives are presented, and then the application of azulene-based optoelectronic materials in organic field-effect transistors and solar cells is discussed. Finally, the challenges and outlook on developing azulene-based optoelectronic materials are discussed, together with several key points on molecular design and synthesis.