Patent ID: 8017221

Claim:
A memory switch comprising a fluoresceine derivative having the formula: wherein —X 1 , X 2 , X 3 , X 4 and Y 1 , Y 2 , Y 3 , Y 4 are independently H, an electron withdrawing group, an alkyl, aryl, aralkyl, alkenyl, or alkynyl group, or a heterocyclic group; the dashed line represents a covalent bond or no bond; J 1 , is O (oxygen), when the dashed line represents a covalent bond, and a O—K group or O − , when the dashed line represents no bond; and J 2 is independently an O—K group or O − ; wherein K is independently H, an alkyl, aryl, aralkyl, alkenyl, or alkynyl group, a trialkyl-silyl group, a benzensulfonyl group, or a heterocyclic group, and Z + is a sulfonate cation having the formula R a —SO 2 + , wherein R a is an alkyl group with 1 to 30 carbon atoms, provided that at least one of J 1 and J 2 is a O − and then f is 1 or 2, with the further proviso that the sulfonate cation is not a cationic polymer.