Acylphosphine oxide photoinitiators

An acylphosphine oxide photoinitiator selected from the group consisting of:

• or
• the acylphosphine oxide photoinitiator is a compound according to Formula (I) or (IV):
• wherein
• n represents an integer having a value of 0 or 1;
• R2 is selected from the group consisting of hydrogen, an alkyl group, an alkoxy group, a group according to Formula (I-a), a —NH—C(═O)—R26 group, a —NH—C(═O)—O—R27 group, and a —NH—C(═)O—NH—R28 group;
• R26 to R28 are independently selected from the group consisting of an alkyl group, an aryl group, an alkenyl group, an alkynyl group, an alkaryl group, an aralkyl group, and a heteroaryl group;
• R1, R3, R4, and R5 are independently selected from the group consisting of hydrogen, an alkyl group, an alkoxy group, and a group according to Formula (I-a);
• at least one of R1 to R5 is a group substituted by a thiol or a group according to Formula (I-a):
• wherein
• Q is a z-valent linking group containing 6 to 30 carbon atoms in which z=k+p+m and z≤6, k=1 to z-p-m, p=0 to 2, and m=1 to 5;
• A is a group according to Formula (I-b):
• wherein
• R1 to R5 have a same meaning as a meaning in Formula (I) in which Q is coupled to the aromatic ring of A in any one of positions occupied by R1 to R5;
• R8 and R9 are independently selected from the group consisting of an alkyl group, an aryl group, an alkoxy group, and an aryloxy group;
• R10 represents an alkyl group substituted by a thiol or an aryl group substituted by a thiol;
• R6 is selected from an alkyl group, an aryl group, an alkoxy group, and an aryloxy group if n=0, and if n=1 R6 represents an alkyl group substituted by a thiol or an aryl group substituted by a thiol;
• R7 is selected from the group consisting of an alkyl group, an aryl group, an alkoxy group, an aryloxy group, and a group according to Formula (I-c):
• wherein
• R1 to R6 and n have a same meaning as a meaning in Formula (I);
• s is an integer having a value of 0 to 4;
• t is an integer having a value of 1 to 5;
• u=s+t+1;
• and
• L represents a u-valent linking group having 2 to 16 carbon atoms;
• R16 and R21 are independently selected from the group consisting of hydrogen, an alkyl group, an alkoxy group, a group according to Formula (I-a), a —NH—C(═O)—R26 group, a —NH—C(═O)—O—R27 group, and a —NH—C(═)O—NH—R28 group;
• R26 to R28 are independently selected from the group consisting of an alkyl group, an aryl group, an alkenyl group, an alkynyl group, an alkaryl group, an aralkyl group, and a heteroaryl group;
• R15, R17 to R20, and R22 to R24 are independently selected from the group consisting of hydrogen, an alkyl group, and an alkoxy group;
• at least one of R15 to R19 is a group substituted by a thiol and at least one of R20 to R24 is a group substituted by a thiol;
• and
• R25 is selected from the group consisting of an alkyl group, an alkenyl group, an alkynyl group, an alkaryl group, an aralkyl group, an aryl group, a heteroaryl group, an alkoxy group, and an aryloxy group;
• wherein
• one or more of the groups R5, R6, R10, and R15 to R24 are substituted by a thiol represented by Formula (II):
• wherein
• * represents a point of attachment;
• X is selected from the group consisting of O, S, and NR11;
• L represents a divalent linking group including no more than 15 carbon atoms;
• n represents 0 or 1;
• R11 is selected from the group consisting of a hydrogen, an alkyl group, an alkenyl group, an alkynyl group, an alkaryl group, an aralkyl group, an aryl or heteroaryl group, and NR12R13;
• R12 and R13 are independently selected from the group consisting of a hydrogen, an alkyl group, an alkenyl group, an alkynyl group, an alkaryl group, an aralkyl group, an aryl, a heteroaryl group, and an acyl group;
• or
• one of the groups R3, R4, R5, R6, R10, and R15 to R24 are substituted by a thiol represented by Formula (III):
• wherein
• * represents a point of attachment;
• o represents an integer selected from 0 and 1;
• m and n independently represent an integer selected from 1 to 5;
• L represents an n+m-valent linking group including no more than 15 carbon atoms;
• and
• R14 is selected from the group consisting of a hydrogen and an alkyl group.