The chemical background for design of infrared sensitizing dyes newly introduced into the donor film for Pictrography 3000 is described. 1) Stabilization of Infrared Cyanine Dyes: The rates of oxidation by FeCl₃ or by O₂ of various infrared cyanine dyes were measured in aqueous acetonitrile solutions. The rates decreased with an increase in oxidation potential and also with an increase in bulkiness of substituents. Since these parameters are mutually independent, introduction of bulky group prevented infrared sensitizing dyes from oxidative degradation without affecting the redox potential which is essential for the sensitizing function. 2) Design of IR-J-Band Sensitizing Dyes: Relationship between structure and aggregation behavior of thiadicarbocyanine dyes were studied. Substituents on the bridging group of the methyne chain have essential effect on aggregation and tuning of wavelength of J- band. An unusual bathochromic shift of J- band due to the mixed aggregate formation was observed for the special combination of thiadicarbocyanines.