Sulfonium derivatives and their use as latent acids

Formula (I) [wherein Ar 1 is, for example, either unsubstituted or substituted phenylene or biphenylene, and Ar 2 and Ar 3 are, for example, independently of each other, both optionally Substituted phenyl, naphthyl, biphenylyl or heteroaryl, or Ar 1 and Ar 2 together with, for example, a direct bond, O, S or (CO) to form a fused ring system, R is For example, hydrogen, C 3 -C 30 cycloalkyl or C 1 -C 18 alkyl, wherein R 1 , R 2 and R 3 are independently of each other, eg, C 1 -C 10 haloalkyl] It is an effective photoacid generator (PAG).