Compounds of the formula (I), (II) or (III), wherein R1 is for example C1-C18alkylsulfonyl, C1-C10haloalkylsulfonyl, camphorylsulfonyl, phenyl-C1-C3alkylsulfonyl, phenylsulfonyl, naphthylsulfonyl, anthrylsulfonyl, phenanthrylsulfonyl or heteroarylsulfonyl, R′1 is for example phenylenedisulfonyl, R2 is for example CN, C1-C10haloalkyl or C1-C10haloalkyl which is substituted by (IV); Ar1 is for example phenyl optionally substituted by a group of formula (IV); Ar′1 is for example phenylene which optionally is substituted by a group of formula (IV); A1, A2 and A3 independently of each other are for example hydrogen, halogen, CN, or C1-C18alkyl; D2 is for example a direct bond, O, (CO)O, (CO)S, SO2, OSO2 or C1-C18alkylene; or A3 and D2 together form C3-C30cycloalkenyl; or A2 and D2 together with the carbon of the ethylenically unsaturated double bond to which they are attached form C3-C30cycloalkyl; D3 and D4 for example independently of each other are a direct bond, O, S, C1-C18alkylene or C3-C30cycloalkylene provided that at least one of the radicals R2, Ar1 or Ar′1 comprises a group of the formula (IV); are suitable as photolatent acid donors and for the preparation of corresponding polymers to be employed in chemically amplified photoresists.