Sulfonium salt photoinitiators and use thereof

A sulfonium salt photoinitiator having the structural formula:

• where
• R1, R2, R3 and R4 are independently a C1-24 alkoxy, a C1-24 alkyl, an aryl, H, Cl, Br, I or F, wherein at least one of R1, R2, R3 or R4 is a halogen,
• Y1, Y2, Y3, Y4, Y5 and Y6 are independently Z or R1-4, wherein at least one of Y1, Y2, Y3, Y4, Y5 or Y6 is Z,
• Z is SAr2+·M−, wherein Ar is phenyl, C1-24 alkyl phenyl, C1-24 alkoxyphenyl, acyl, thiophenyl, phenylthiophenyl, C1-24 alkylthiophenyl, C1-24 dialkyl substituted phenylthiophenyl, or C1-24 dialkoxy substituted phenylthiophenyl, and M− is SbF6−, PF6−, AsF6−, BF4−, B(C6F5)4− or Ga(C6F5)4−.