Exploring the Synthesis and Characteristics of Nanographenes and PAHs with Azulene Embedment

Azulene, characterized as a non-alternant aromatic hydrocarbon, is an isomer of naphthalene, featuring a 10-π-electron system and a notable high dipole moment. An intriguing aspect is the electron-rich nature of the five-membered ring in azulene, in contrast to the electron-poor seven-membered ring. The unique donor-acceptor structure makes azulene well-suited for intermolecular charge transfer properties, contributing to its utility in the development of advanced optoelectronic materials. Moreover, when contiguous pentagonal and heptagonal rings are present, they induce structural defects within molecular systems, leading to various alterations such as twisting, helical arrangements, and wrapping phenomena. These structural perturbations significantly impact the electronic, magnetic, and overall structural properties of the fused molecules, introducing complexities in their behavior and functionality. Researchers have fused or connected azulene with various chromophoric moieties to explore their photophysical and biological attributes. Notably, a diverse range of large-π-conjugated ring systems, such as nanographenes, porphyrins, phthalocyanines, corroles, calixarenes, naphthalene and perylene diimides, polymers, BODIPY's, polycyclic aromatic hydrocarbons (PAHs), have been integrated with azulene for comprehensive property investigations. Applications of azulene-based molecules span a wide spectrum, encompassing IR absorption materials, organic solar cells, organic semiconductors, nonlinear optical materials, conducting polymers, and organic field-effect transistors. This chapter endeavors to offer a comprehensive overview encompassing the synthesis methodologies and diverse array of properties exhibited by expansive structures integrating azulene such as nanographenes and PAHs. An investigation of these systems will provide a deeper understanding of their structural properties and functional capabilities, thereby shedding light on the significance of these systems in materials science and beyond.