Patent ID: 8540521

Claim:
A compound of the formula: or a salt thereof, wherein M is —NCH 2 -Py or —N(CH 2 COOR 5 ) 2 , wherein R 5 is H, an alkyl having 1-6 carbons, —CH 2 OCOCH 3 , or a counterion; Y is —CH 3 , —CH 2 COOH, —CH 2 COOPy, or X is —N(CH 2 COOR 5 ) 2 , —NCH 2 Py, —OCH 2 Py, or —OCH 2 COOR 5 ; R 7 , R 8 , R 9 , and R 10 are independently selected from the group consisting of an alkyl having 1-6 carbons, halogen, amino, nitro, cyano, trifluoromethyl, sulfo, and sulfonamide; R 1 and R 2 are independently H, an alkyl having 1-6 carbons, halogen, or sulfo; R 4 is a 5 or 6-membered aromatic ring or a fused ring system comprising at least one 6-membered aromatic ring; L is an alkylene having 2-6 carbons; and p is 0 or 1.