A compound which is a quaternary ammonium salt of Formula II: where: X is a negatively charged counterion; Y is N or C-R 7, where R 7 is selected from the group consisting of H, C1-C6 alkyl, C1-C6 alkoxy and groups of Formula VI where * is the point of attachment, and where T is selected from O, NH, N(C1-C6 alkyl) and a direct link; m is selected from integers from 0 to 6; U is selected from OR 44, CF 3, OCF 3, CN, NR 45 R 46, pyrrolidinyl, piperidinyl, piperazinyl, N1-methylpiperazinyl, morpholinyl, CON(R 47)(R 48), SO 2 N(R 49)(R 50), N(R 51)COR 52, N(R 53)SO 2 R 54, COR 55, SOR 56, SO 2 R 57 and COOR 58; and R 42, R 43, R 44, R 45, R 46, R 47, R 48 R 49, R 50, R 51, R 52, R 53, R 54, R 55, R 56, R 57, R 58 are independently selected from H and C1-C6 alkyl; Z is N or C-CN; n is an integer from 0 to 6; R 1 is a group of the formula IIId: where * is the point of attachment, R 8 is selected from H and C1-C3 alkyl, and R 9 is selected from H and C1-C6 alkyl; R 2 and R 3 are independently selected from C1-C6 alkyl, cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, CH 2 CH 2 OH, and CH 2 CH 2 O(C1-C6 alkyl), or R 2 and R 3 may together form a non-aromatic carbocyclic ring or non-aromatic heterocyclic ring containing at least one heteroatom; R 5 is selected from anilines, indoles, indoline, amines, aminoindoles and aminoindazoles, each of which may be optionally substituted with one or more substituents selected from H, C1-C6 alkyl, C2-C6 alkenyl, C2-C6 alkynyl, C1-C6 alkoxy, F, Cl, Br, I, CN, CH 2 F, CHF 2, CF 3, OH, NH 2, NO 2, NH(C1-C6 alkyl), N(C1-C6 alkyl) 2, CONH 2, CO(C1-C6 alkyl), SO 2 NH 2 and SO 2 (C1-C6 alkyl); and R 6 is selected from H, C1-C6 alkyl, C1-C6 alkoxy, NH(C1-C6 alkyl), N(C1-C6alkyl) 2 and groups of Formula V where * is the point of attachment; V is selected from (CH 2) k where k is an integer from 0 to 6, O, NH and N(C1-C6 alkyl); and R 41 is selected from H and C1-C6 alkyl. X is a negatively charged counterion; Y is N or C-R 7, where R 7 is selected from the group consisting of H, C1-C6 alkyl, C1-C6 alkoxy and groups of Formula VI where * is the point of attachment, and where T is selected from O, NH, N(C1-C6 alkyl) and a direct link; m is selected from integers from 0 to 6; U is selected from OR 44, CF 3, OCF 3, CN, NR 45 R 46, pyrrolidinyl, piperidinyl, piperazinyl, N1-methylpiperazinyl, morpholinyl, CON(R 47)(R 48), SO 2 N(R 49)(R 50), N(R 51)COR 52, N(R 53)SO 2 R 54, COR 55, SOR 56, SO 2 R 57 and COOR 58; and R 42, R 43, R 44, R 45, R 46, R 47, R 48 R 49, R 50, R 51, R 52, R 53, R 54, R 55, R 56, R 57, R 58 are independently selected from H and C1-C6 alkyl; Z is N or C-CN; n is an integer from 0 to 6; R 1 is a group of the formula IIId: where * is the point of attachment, R 8 is selected from H and C1-C3 alkyl, and R 9 is selected from H and C1-C6 alkyl; R 2 and R 3 are independently selected from C1-C6 alkyl, cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, CH 2 CH 2 OH, and CH 2 CH 2 O(C1-C6 alkyl), or R 2 and R 3 may together form a non-aromatic carbocyclic ring or non-aromatic heterocyclic ring containing at least one heteroatom; R 5 is selected from anilines, indoles, indoline, amines, aminoindoles and aminoindazoles, each of which may be optionally substituted with one or more substituents selected from H, C1-C6 alkyl, C2-C6 alkenyl, C2-C6 alkynyl, C1-C6 alkoxy, F, Cl, Br, I, CN, CH 2 F, CHF 2, CF 3, OH, NH 2, NO 2, NH(C1-C6 alkyl), N(C1-C6 alkyl) 2, CONH 2, CO(C1-C6 alkyl), SO 2 NH 2 and SO 2 (C1-C6 alkyl); and R 6 is selected from H, C1-C6 alkyl, C1-C6 alkoxy, NH(C1-C6 alkyl), N(C1-C6alkyl) 2 and groups of Formula V where * is the point of attachment; V is selected from (CH 2) k where k is an integer from 0 to 6, O, NH and N(C1-C6 alkyl); and R 41 is selected from H and C1-C6 alkyl.