Photoconductivity of Some Cyanine Dyes*

An examination of the properties of pinacyanole, dicyanine-A, kryptocyanine, and neocyanine indicates that the cyanine dyes constitute a distinct class of photoconductive dyes which differ from those previously studied in being without a high density of monoenergetic traps. In consequence, their responses are fast and relatively independent of temperature. The characteristics of cells depend very sensitively on details of preparation, and the level of photoconductivity of a given cell depends more on the homogeneity of the dye film than on the properties of the dye. Evidence is given that the polymer form of pinacyanole is present in some films, and that a rate-modifying process is associated with light absorbed by it. It is concluded that the properties of these dyes are such as not to preclude the charge carrier transfer mechanism of optical sensitization.