Mar. 26, 2015  14  US 2015/0086912 Al  [0188]  Of the cationic structures represented by formulae  (ZI-1) to (ZI-3), preferred are (ZI-1) and (ZI-2), and more  preferred is (ZI-1 ).  [0189]  In the next place, (ZA-1-2) is described.  [0190]  (ZA-1-2) represents an organic group in which each  ofR$_{201 }$to R$_{203 }$in (ZI-1) independently represents an organic  group not having an aromatic ring. The aromatic ring here  means to include an aromatic ring containing a heteroatom.  [0191]  The organic group not containing an aromatic ring  as R$_{201 }$to R$_{203 }$is generally an organic group having  1  to 30  carbon atoms, and preferably  1  to 20 carbon atoms.  [0192]  Each ofR$_{201 }$to R$_{203 }$independently preferably rep› resents an alkyl group, a monovalent aliphatic hydrocarbon  cyclic group, an ally! group, or a vinyl group, more preferably  a linear or branched 2-oxoalkyl group, 2-oxo aliphatic hydro› carbon cyclic group, or alkoxycarbonylmethyl group, and  especially preferably a linear or branched 2-oxo aliphatic  hydrocarbon cyclic group.  [0193]  As the alkyl group and aliphatic hydrocarbon cyclic  group ofR$_{201 }$to R$_{203}$, a linear or branched alkyl group having  1  to  10  carbon atoms (e.g., a methyl group, an ethyl group, a  propyl group, a butyl group, a pentyl group), and an aliphatic  hydrocarbon cyclic group having 3 to  10  carbon atoms ( e.g.,  a cyclopentyl group, a cyclohexyl group, a norbonyl group)  can be preferably exemplified. The alkyl group is more pref› erably a 2-oxoalkyl group and an alkoxycarbonylmethyl  group. The aliphatic hydrocarbon cyclic group is more pref› erably a 2-oxo aliphatic hydrocarbon cyclic group. The ali› phatic hydrocarbon cyclic group is preferably a cycloalkyl  group.  [0194]  The 2-oxoalkyl group may be either linear or  branched, and is preferably a group having >C=O at the  2-position of the above alkyl group.  [0195]  The 2-oxo aliphatic hydrocarbon cyclic group is  preferably a group having >C=O at the 2-position of the  above aliphatic hydrocarbon cyclic group. The 2-oxo ali› phatic hydrocarbon cyclic group is preferably a 2-oxocy› cloalkyl group.  [0196]  The alkoxy group in the alkoxycarbonylmethyl  group is preferably an alkoxy group having  1  to 5 carbon  atoms (e.g., a methoxy group, an ethoxy group, a propoxy  group, a butoxy group, a pentoxy group).  [0197]  R$_{201 }$to R$_{203 }$may further be substituted with a halo› gen atom, an alkoxy group ( e.g., having  1  to 5 carbon atoms),  a hydroxyl group, a cyano group, or a nitro group.  [0198]  (ZA-1-3) is described in the next place.  [0199]  (ZA-1-3) is a group represented by the following  formula, and is a group having a phenacylsulfonium salt  structure.  [0200]  In formula (ZA-1-3), each ofR$_{1}$c to R$_{5}$c indepen› dently represents a hydrogen atom, an alkyl group, a monova› lent aliphatic hydrocarbon cyclic group, an alkoxy group, a  phenylthio group, or a halogen atom.  [0212]  As the cyclic structure which may be formed by  bonding Rx and Ry to each other, a 5- or 6-membered ring  formed by divalent groups Rx and Ry (e.g., a methylene  group, an ethylene group, a propylene group, and the like)  [0211]  Each of Rx and Ry preferably represents an alkyl  group having  4  or more carbon atoms or a monovalent ali› phatic hydrocarbon cyclic group, more preferably an alkyl  group having 6 or more carbon atoms, and still more prefer› ably an alkyl group having 8 or more carbon atoms or a  monovalent aliphatic hydrocarbon cyclic group.  [0210]  As for the alkoxy group in the alkoxycarbonylm› ethyl group, the alkoxy group same as those in R$_{1 }$c to R$_{5}$c can  be exemplified.  [0209]  As the 2-oxoalkyl group and 2-oxo aliphatic hydro› carbon cyclic group, the alkyl group and the group having  >C=O at the 2-position of the aliphatic hydrocarbon cyclic  group as R$_{1 }$c to R$_{7}$c can be exemplified.  [0208]  As the alkyl group and monovalent aliphatic hydro› carbon cyclic group as Rx and Ry, the same alkyl group and  monovalent aliphatic hydrocarbon cyclic group as in R$_{1 }$c to  R$_{7}$c can be exemplified, and more preferably a 2-oxoalkyl  group, a 2-oxo aliphatic hydrocarbon cyclic group, and an  alkoxycarbonylmethyl group.  [0207]  Preferably any ofR$_{1}$c to R$_{5}$c is a linear or branched  alkyl group, a monovalent aliphatic hydrocarbon cyclic  group, or a linear, branched or cyclic alkoxy group, and more  preferably the sum total of the carbon atoms ofR$_{1}$c to R$_{5}$c is  2 to 15, by which the solubility of solvent is improved and the  generation of particles during preservation is controlled.  [0206]  The alkoxy group as R$_{1 }$c to R$_{5}$c may be linear,  branched or cyclic, and the examples thereof include an  alkoxy group having  1  to  10  carbon atoms, and preferably a  linear or branched alkoxy group having  1  to 5 carbon atoms  ( e.g., a methoxy group, an ethoxy group, a linear or branched  propoxy group, a linear or branched butoxy group, and a  linear or branched pentoxy group), a cyclic alkoxy group  having 3 to 8 carbon atoms ( e.g., a cyclopentyloxy group and  a cyclohexyloxy group).  [0205]  The monovalent aliphatic hydrocarbon cyclic group  as R$_{1 }$c to R$_{7}$c may be either monocyclic or polycyclic, and the  examples thereof include a monovalent aliphatic hydrocar› bon cyclic group having 3 to 8 carbon atoms ( e.g., a cyclo› pentyl group and a cyclohexyl group). The monovalent ali› phatic hydrocarbon cyclic group is preferably a cycloalkyl  group.  [0204]  The alkyl group as R$_{1 }$c to R$_{7}$c may be either linear or  branched, and the examples thereof include an alkyl group  having  1  to 20 carbon atoms, and preferably a linear or  branched alkyl group having  1  to 12 carbon atoms (e.g., a  methyl group, an ethyl group, a linear or branched propyl  group, a linear or branched butyl group, and a linear or  branched pentyl group).  [0203]  Any two or more ofR$_{1 }$c to R$_{5}$c, R$_{6}$c and R$_{7}$c, and Rx  and Ry may be bonded to each other to form a ring, and the  ring may contain an oxygen atom, a sulfur atom, an ester  bond, or an amido bond. As the group formed by bonding any  two or more of R$_{1 }$c to R$_{5}$c, R$_{6}$c and R$_{7}$c, and Rx and Ry, a  butylene group and a pentylene group can be exemplified.  [0202]  Each of Rx and Ry independently represents an  alkyl group, a monovalent aliphatic hydrocarbon cyclic  group, an ally! group, or a vinyl group.  [0201]  Each of R$_{6}$c and R$_{7}$c independently represents a  hydrogen atom, an alkyl group, or a monovalent aliphatic  hydrocarbon cyclic group.  (ZA-1-3)  Rx  I  s  01  Ry 