Design, Synthesis, and Electronic Properties of Near-Infrared Absorbing Phthalocyanine Analogues

In recent years, much effort has been made to develop various types of near-infrared organic compounds because of their potential applications in organic solar cells, photodynamic therapy for cancer, and fluorescence bioimaging. Although a common strategy to achieve bathochromic shifts of the absorption maximum of a dye is the extension of the π-electron system, chemical stability of the π-extended system usually decreases with increasing extension. Phthalocyanine derivatives are an important group of visible-light-absorbing compounds, because they are more stable to heat and light than other types of organic dyes. In order to develop stable near-infrared dyes, we designed and created new types of phthalocyanine analogues, azulenocyanines (1), aromatic hemiporphyrazines (2), benziphthalocyanines (3), and expanded phthalocyanines (4). Design strategy, synthesis, and unique properties of these compounds are reported.