Fluorescent ion indicators and their applications

A compound of Formula 1:

• or a salt thereof, wherein:
• Y8 is CR8 or C covalently bonded to N, and
• Y9 is CR9 or C covalently bonded to N, wherein one of Y8 and Y9 is C covalently bonded to the N;
• R1 to R10 are independently selected from H, halogen, carboxy, substituted carboxy, alkyl, substituted alkyl, alkoxy, substituted alkoxy, aryloxy, substituted aryloxy, thiol, alkylthiol, arylthiol, azido, nitro, nitroso, cyano, amino, substituted amino, hydroxy, phosphonyl, sulfonyl, carbonyl, boronic acid, aryl, substituted aryl, heteroaryl, and substituted heteroaryl;
• m and n are independently an integer from 0 to 3, wherein the sum of m+n is ≥2;
• W is O, N—R31, C(R31R32), Si(R31R32), S═O, O═S═O, P═R32, O═P—R32, O═P—OR32, or B(OR31), wherein R31 and R32 are independently selected from H, alkyl, substituted alkyl, aryl, substituted aryl, heteroaryl, and substituted heteroaryl;
• X and Y are independently acyl, substituted acyl, acyloxymethyl or substituted acyloxymethyl;
• and
• Z is substituted aryl, wherein Z is substituted at the alpha position with a heteroatom-containing substituent capable of bonding to a chelated metal ion.