Sensor dyes for real-time sensing of metal ions in aqueous environments

A compound of formula (II):

• wherein each R is independently selected from the group consisting of OH, H, OR1, C1-4 alkyl, nitro, halo, NRN1RN2, SO3H, SO2NHR3, NHSO2R4, carboxyl, amido, nitrile, —C(═N—OH)R3, —C(═O)NRN1OH, —SR5, thioamido, phosphonate or two Rs may join together to form a 5, 6, or 7-membered ring, which may be aromatic or heteroaromatic, which may be substituted;
• each A is independently N, NO, CH, or CR5;
• RN1 and RN2 are independently C(O)R2, heteroaryl, aryl, C1-4 alkyl,
• or H;
• Ra is an amino acid side chain;
• each R1 is independent C1-4 alkyl, C2-4 alkenyl, heteroaryl, or aryl;
• each R2 is independently C1-4 alkyl, C2-4 alkenyl, heteroaryl, or aryl;
• each R3 is independently H, C1-4 alkyl, heteroaryl, aryl, cycloalkyl, or heterocyclyl;
• each R4 is independently H, C1-4 alkyl, heteroaryl, aryl, cycloalkyl, or heterocyclyl;
• each R5 is independently H, C1-4 alkyl, heteroaryl, aryl, cycloalkyl, or heterocyclyl;
• and
• each n is independently an integer from 1 to 5;
• wherein the compound of Formula (I) is not 4-(2-pyridylazo)rescorinol (PAR) or 4-(quinolin-8-yldiazenyl)benzene-1,3-diol (QAR).

A compound according to formula (IV):

• A-B (IV)
• wherein A is selected from the group consisting of:
• wherein R1, R2, R3 and R4 are independently selected from:
• B is selected from the group consisting of:
• wherein the compound of Formula (IV) is not 4-(2-pyridylazo)rescorinol (PAR) or 4-(quinolin-8-yldiazenyl)benzene-1,3-diol (QAR).