Photosensitive composition

1 . A photosensitive composition comprising:

(A) a sensitizing dye;

(B) an initiating compound capable of generating a radical, an acid or a base; and

(C) a polymerizable compound capable of reaction by at least one of a radical, an acid and a base,

wherein the sensitizing dye is a compound selected from a compound having a partial structure represented by formula (1) and a compound represented by formula (I):

wherein Ar represents an aromatic ring;

A represents —NR 3 R 4 , —SR 5 or —OR 6 ;

R 1 , R 2 and R 3 to R 6 each independently represents a hydrogen atom or a monovalent nonmetallic atomic group; and

Z − represents a counter ion necessary for neutralizing electric charge;

wherein X 1 and X 1 ′ each independently represents an oxygen atom, a sulfur atom, —CR 5 R 6 or —NR 7 —, and at least one of X 1 and X 1 ′ represents an oxygen atom, a sulfur atom or —NR 7 —;

R 1 , R 2 , R 3 , R 4 , R 5 , R 6 and R 7 each independently represents a hydrogen atom or a monovalent nonmetallic atomic group;

Y represents an oxygen atom, a sulfur atom or NR 8 ;

A and A′ each independently represents an aromatic ring or a heterocyclic ring, which may have a substituent;

R 3 and R 4 each represents a nonmetallic atom or a nonmetallic atomic group that is bonded to any moiety of A and A′ to form a cyclic structure; and

R 1 to R 8 may be bonded to each other to form an aliphatic or aromatic ring.

2 . The photosensitive composition according to claim 1 ,

wherein the sensitizing dye is a compound having a partial structure represented by formula (1).

3 . The photosensitive composition according to claim 1 ,

wherein the sensitizing dye is a compound represented by formula (I).

4 . The photosensitive composition according to claim 1 ,

wherein the sensitizing dye is a compound represented by formula (2):

wherein R 11 , R 12 , R 13 , R 14 , R 15 , R 16 , R 17 and R 18 each independently represents a hydrogen atom or a monovalent nonmetallic atomic group, or may be bonded to each other to form a ring, provided that at least one of R 11 , R 13 and R 15 represents —NR 19 R 20 , —SR 21 or —OR 22 ;

R 19 , R 20 , R 21 and R 22 each independently represents a hydrogen atom or a monovalent nonmetallic atomic group.

5 . The photosensitive composition according to claim 1 ,

wherein the initiating compound capable of generating a radical, an acid or a base is a hexaarylbiimidazole compound.

6 . The photosensitive composition according to claim 1 ,

wherein the polymerizable compound capable of reaction by at least one of a radical, an acid and a base is an addition polymerizable compound having an ethylenic unsaturated double bond.

7 . A lithographic printing plate precursor comprising a photosensitive layer that comprises a photosensitive composition according to claim 1.