Patent ID: 7652138

Claim:
A compound of formula 1 wherein: A is X − is an anion with a single negative charge; R 1 and R 2 are each independently a C 1 -C 4 -alkyl optionally substituted with hydroxy or halogen; R 3 and R 5 are each independently C 1 -C 4 -alkyl, C 1 -C 4 -alkyloxy, hydroxy, CF 3 , CN, NO 2 , or halogen; and R 4 , R 6 , R 7 , and R 8 are each independently hydrogen, C 1 -C 4 -alkyl, C 1 -C 4 -alkyloxy, hydroxy, CF 3 , CN, NO 2 , or halogen.