Compounds of the formula wherein M is either (1) a metal ion having a positive charge of +y wherein y is an integer which is at least 2, said metal ion being capable of forming a compound with at least two chromogen moieties, or (2) a metal-containing moiety capable of forming a compound with at least two chromogen moieties, z is an integer representing the number of chromogen moieties associated with the metal and is at least 2, R1, R2, R3, R4, R5, R6, R7, a, b, c, d, Y, and z are as defined herein, Q− is a COO− group or a SO3— group, A is an organic anion, and CA is either a hydrogen atom or a cation associated with all but one of the Q− groups.