Azulene-Based Molecules, Polymers, and Frameworks for Optoelectronic and Energy Applications

Azulene has a considerably larger dipole moment than its isomer naphthalene; it also has unique physicochemical properties, including different reactivities on five- and seven-membered rings, a dark color, a narrow gap between the highest occupied molecular orbital and lowest unoccupied molecular orbital, and stimulus response. Although azulene was discovered more than 100 years ago, the use of azulene-based derivatives can be traced back to five centuries ago. Due to its unusual structure, azulene-based molecules and materials are widely used in various fields. However, studies on azulene-based materials have long been hindered by difficulties in the synthesis. Considerably fewer studies have been conducted on azulene-based derivatives than on naphthalene-based derivatives. This perspective paper mainly introduces recent reports on the synthesis of azulene-based aromatic molecules, conjugated polymers, and coordination polymers, in addition to azulene-based frameworks. The structure-property relationship, optoelectronic applications, and energy-related applications of azulene-based derivatives are reviewed, including their use in near-infrared absorption, organic field-effect transistors, organic solar cells, and microsupercapacitors.