Fluorogenic pH-sensitive compounds and their methods of use

A compound chosen from a compound of Formula (I):

• its corresponding compound of Formula (II)
• wherein,
• O—X—Y is chosen from:
• R1, R2, R3, and R4 are each independently chosen from H, alkyl, substituted alkyl, alkenyl, substituted alkenyl, alkynyl, substituted alkynyl, cyano, halo, hydroxy, nitro, sulfo, sulfonyl, sulfonyloxy, thioacyl, thiol, alkylthio, substituted alkylthio, acyl, aryl, substituted aryl, heteroaryl, substituted heteroaryl, cycloalkyl, substituted cycloalkyl, heterocyclyl, and substituted heterocyclyl;
• and
• D is
• wherein
• R5, R6, R7 and R8 are each independently chosen from H and alkyl;
• and
• R9, R10, R11 and R12 are each independently chosen from H, alkyl, sulfo and sulfonyl;
• or
• R8 is taken together with R12 and the atoms to which they are attached to form an optionally substituted fused ring;
• or R9 is taken together with R5 and the atoms to which they are attached to form an optionally substituted fused ring;
• or R10 is taken together with R7 and the atoms to which they are attached to form an optionally substituted fused ring;
• or R11 is taken together with R6 and the atoms to which they are attached to form an optionally substituted fused ring, and salts thereof.