System for interacting with analog-printed substrate

A system for interacting with a coded substrate, said system comprising:

• a substrate having human-readable information and machine-readable coded data disposed thereon or therein;
• and
• a sensing device for reading the machine-readable coded data,
• wherein said coded data comprises an IR-absorbing phthalocyanine dye comprising one or more sulfonate groups, wherein a counterion of at least one sulfonate group is a phosphonium cation,
• and wherein:
• each phosphonium cation is of formula:
• P+(Rm)(Rn)(Rs)(Rt);
• each of Rm, Rn, Rs and Rt is independently selected from the group consisting of:
• C1-30 alkyl, C5-12 aryl and C5-30 arylalkyl;
• and
• at least one of Rm, Rn, Rs and Rt comprises more than 4 carbon atoms.