Chemically amplified photoresist compositions comprising,(a) a compound which cures upon the action of an acid or a compound whose solubility is increased upon the action of an acid; and (b) a compound of the formula Ia, Ib, IIa, IIb, IIIa, IIIb, IVa, IVb, Va, Vb or VIa wherein n is 1 or 2; m is 0 or 1; X0 is —[CH2]h—X or —CH═CH2; h is 2, 3, 4, 5 or 6; R1, when n is 1, is for example optionally substituted phenyl, naphthyl, anthracyl, phenanthryl, or heteroaryl; R1, when n is 2, is for example optionally substituted phenylene or naphthylene; R2 for example has one of the meanings of R1; X is for example —OR20, —NR21R22, —SR23; X′ is —X1-A3-X-; X1 and X2 are for example —O—, —S— or a direct bond; A3 is e.g. phenylene; R3 has for example one of the meanings given for R1; R4 has for example one of the meaning given for R2; R5 and R6 e.g. are hydrogen; G i.a. is —S— or —O—; R7 when n is 1, e.g. is phenyl, optionally substituted, when n is 2, is for example phenylene; R8 and R9 e.g. are C1-C18alkyl; R10 has one of the meanings given for R7; R11 i.a. is C1-C18alkyl; R12, R13, R14, R15 R16, R17 and R18 for example are hydrogen or C1-C18alkyl; R20, R21, R22 and R23 i.a. are phenyl or C1-C18alkyl; give high resolution with good resist profile.