The design of blue-light-sensitive layers in film systems can be limited by the relatively low extinction coefficients of chromogenically formed yellow imaging dyes. The release of a preformed dye from part of the coupling-off group of a coupler increases the effective extinction and is useful provided the dye is shifted to be colorless or nearly so, when part of the coupler. The overall hue of the dyes formed must be equivalent to the hue of the conventional dye system, and the incorporation of the dye into the coupling-off group cannot adversely affect the rate of reaction with oxidized color developer. In previous work on releasable dyes with phenolic chromophores, the dyes suffered from deficiencies that the hue was sensitive to pH, and often mordants were needed to prevent hue shifting. Such problems are overcome by using uncharged azo and methine chromophores. Release of the dye is made from carbamate precursors, which are, in turn, directly or indirectly linked to the coupling site of the coupler. The formation of the dye carbamate results in hypsochromic hue shifting of almost 100 nm.
David Hoke, Jared B. Mooberry, James J. Seifert, David T. Southby, Zheng Z. Wu, "High-Extinction Dyes from Yellow Imaging Couplers: The Release of a Preformed Dye from the Coupling-Off Group" in Journal of Imaging Science and Technology, 1998, pp 528 - 533, https://doi.org/10.2352/J.ImagingSci.Technol.1998.42.6.art00010