Near-Infrared (NIR) Dyes

　Near infrared dyes show light absorption in the near infrared area of 700-2000 nm. Their intense absorption normally originates from a charge transfer of an organic dye or metal complex. Materials of near infrared absorption involve cyanine dyes having an extended polymethine, phthalocyanine dyes with a metal center of aluminum or zinc, naphthalocyanine dyes, nickel dithiolene complexes with a square-planar geometry, squarylium dyes, quinone analogues, diimonium compounds and azo derivatives. Applications using these organic dyes include security markings, lithography, optical recording media and optical filters. A laser-induced process requires near infrared dyes having a sensitive absorption of longer than 700 nm, high solubility for appropriate organic solvents, and excellent heat-resistivity. In order to increase power conversion efficiency of an organic solar cell, efficient near infrared dyes are required, because sunlight includes near infrared light. Furthermore, near infrared dyes are expected to be biomaterials for chemotherapy and imaging deep-tissue in-vivo by using luminescent phenomena in the near infrared region.