307  US 9,323,150 B2  308  -continued  Compounds each having two or more of the structures of  general formula  (ZI)  may be used as photoacid generators.  For example, use may be made of a compound with a struc- ture in which at least one of R$_{201 }$ to R$_{203 }$ of any of the  compounds of general formula  (ZI)  is bonded to at least one  of R$_{201 }$ to R$_{203 }$of another of the compounds of general for› mula  (ZI).  As further preferred  (ZI)  components, there can be men- tioned the following compounds (ZI-1) to (ZI-4).  Compounds (ZI-1) are compounds of general formula  (ZI)  above wherein at least one of R$_{201 }$ to R$_{203 }$is an aryl group.  Namely, compounds (ZI-1) are arylsulfonium compounds,  i.e., compounds each containing an arylsulfonium as a cation.  With respect to the compounds (ZI-1), all ofR$_{201 }$ to R$_{203 }$ may be aryl groups. It is also appropriate that R$_{201 }$to R$_{203 }$are  partially an aryl group and the remainder is an alkyl group.  When any of the compounds (ZI-1) contains a plurality ofaryl  groups, the aryl groups may be identical to or different from  each other.  As the compounds (ZI-1), there can be mentioned, for  example, a triarylsulfonium compound, a diarylalkylsulfo› nium compound and an aryldialkylsulfonium compound.  The aryl group contained in the compounds (ZI-1) is pref- erably a phenyl group, a naphthyl group, or a heteroaryl  group, such as an indole residue or a pyrrole residue. A phenyl  group, a naphthyl group and an indole residue are especially  preferred.  The alkyl group contained in the compounds (ZI-1)  according to necessity is preferably a linear, branched or  cyclic alky 1 group having 1 to 15 carbon atoms. As such, there  can be mentioned, for example, a methyl group, an ethyl  group, a propyl group, an n-butyl group, a sec-butyl group, a  t-butyl group, a cyclopropyl group, a cyclobutyl group or a  cyclohexyl group.  Substituents may be introduced in these aryl and alkyl  groups. As the substituents, there can be mentioned, for  ,,J  l  ,o  «Y$^{0 }$ tt’f  "1):1  0  0  F  F  o*o  -o-~  ~_,,,o  II  F  F  II  0  F  0  F  F  o*o  -o-~  !_,,,o  II  F  F  I  0  F  0  0  0  I  -o-s  II  0  F  -o-~  ~  J~  u" t  ’f  0  0  0  II  -o-s  II  0  -o-~-0-\  II  _  0  0  -o-~-p\  II  _  0  ~  -continued 