Photoacid generator compounds and compositions

A compound of formula I:

• wherein
• A1 is I or S;
• n1 is 2 when A1 is I, and n1 is 3 when A1 is S;
• each Ro is independently alkyl, cycloalkyl, heterocycle, aryl, or heteroaryl, each optionally substituted with one to about five substituents;
• A2 is O or N;
• n2 is 1 when A2 is O and n2 is 2 when A2 is N;
• Rf is a diradical carbon chain comprising one to about 20 carbon atoms wherein the chain is optionally interrupted by one to five oxygen atoms, and each carbon atom is substituted with zero to two halo groups, or Rf is a direct bond;
• each R1 is independently H, alkyl, cycloalkyl, heterocycle, aryl, or heteroaryl;
• n3 is 0 to about 10;
• n4 is 1 or 2;
• n5 is 0 to 7;
• and
• any aryl or heteroaryl of formula I is optionally substituted with one to five halo, (C1-C6)alkyl, alkoxy, acyl, alkoxycarbonyl, alkoxyacyl, acyloxy, trifluoromethyl, trifluoromethoxy, hydroxy, cyano, carboxy, nitro, or —N(R2)2 groups;
• any alkyl, cycloalkyl, heterocycle, aryl, or heteroaryl is optionally substituted with one to five halo, (C1-C6)alkyl, alkoxy, acyl, alkoxyacyl, acyloxy, trifluoromethyl, trifluoromethoxy, hydroxy, cyano, carboxy, nitro, —N(R2)2, or oxo groups;
• and
• each R2 is independently H, alkyl, aryl, acyl, or aroyl.