", and X2 and X3 are independently selected from the group consisting of a carboxylate group, a sulfonate group, a sulfate group, a phosphate group, a nitro group, a halo group selected from the group consisting of chloro, bromo, fluoro, and iodo, --CN, an alkoxy group containing from 1 to about 6 carbon atoms, and a group of the formula --R3 OR4 wherein R3 and R4 are an alkyl containing from about" . . . . .