Sensitizer for cationic photoinitiators

A composition comprising an iodonium salt cationic photoinitiator and a polycyclic aromatic compound having the formula (I):

• in which:
• Q represents a residue of a polycyclic aromatic compound having at least two conjugated aromatic rings and having a valency x;
• Y is an aliphatic carbon chain which may be interrupted by one or more oxygen atoms, sulphur atoms, phenylene groups, carbonyl groups, epoxide groups or linear or cyclic carbonate groups;
• p is 0 or 1;
• R1 and R2 are the same as or different from each other, and each represents a hydrogen atom, an alkyl group, a hydroxyalkyl group, an alkoxyalkyl group, an alkoxycarbonylalkyl group or a C2-C5 carbon chain which is attached to a carbon atom of Y to form a fused ring;
• R1 represents a hydrogen atom or an alkyl group;
• and
• m and n are the same as or different from each other, and each is zero or a number from 1 to 4, provided that (m+n) is zero or a number from 1 to 4.