Chris;

These are structural diagrams of organic chemicals. The first two have charged amines in side chains, and the "real" SS dyes have the charged nitrogen in a ring structure called a heterocycle. There is a huge difference between the two types of structure regarding the distribution of charge (electrons) and in the latter case it allows the dye to bind to the surface of the silver halide crystal and to transfer energy from light to the crystal.

The former two may or may not, but even if they do, it would probably be inefficient. Erythrosine is more similar to the former two in a way, and it is quite inefficient in energy transfer and so it is more difficult to use in some cases.

PE