Patent ID: 8192918

Claim:
A lithographic printing plate precursor comprising a support which includes a hydrophilic surface or which is provided with a hydrophilic layer and a coating thereon, said coating comprising an IR absorbing agent, a contrast enhancing compound and a polymeric binder that alters its solubility in an alkaline developing solution upon exposure, wherein said contrast enhancing compound has the structure of formula I: wherein R 1 is hydrogen, an optionally substituted alkyl, alkenyl, alkynyl, aryl, alkaryl, aralkyl or heteroaryl group, halogen, —NR 4 R 5 , —CO—NR 4 R 5 , —SO 2 —NR 4 R 5 , —COR 6 , —CN, —NO 2 , —COOR 6 , —OR 3 , —SR 3 , —SOR 3 , —SO 2 R 6 , —SO 3 R 6 , —PO 4 R 4 R 5 , —PO 3 R 4 R 5 , —NR 6 —CO—NR 4 R 5 , —O—COOR 6 , —NR 4 —COOR 5 , —NR 4 —CO—R 5 or a phosphoramidate group; R 2 is hydrogen, an optionally substituted alkyl, alkenyl, alkynyl, aryl, alkaryl, aralkyl or heteroaryl group, halogen, —SO 2 —NR 4 R 5 , —CN, —NO 2 , —SOR 3 , —SO 2 R 6 , —SO 3 R 6 , —PO 4 R 4 R 5 , —PO 3 R 4 R 5 or a phosphoramidate group; R 3 is an optionally substituted alkyl, alkenyl, alkynyl, aryl, alkaryl, aralkyl or heteroaryl group; R 4 , R 5 and R 6 independently are hydrogen or one of the groups as defined for R 3 , or wherein two groups selected from the group consisting of R 4 , R 5 and R 6 together comprise the atoms necessary to form a ring; Q is one of the following groups which forms an optionally substituted 6 membered heteroaromatic ring, said groups being selected from the group consisting of **—C(T 2 )-N—N—*, **—N—N—C(T 2 )-*, **—N—C(T 2 )-C(T 3 )-*, **—C(T 2 )-N—C(T 3 )-*, **—C(T 2 )-C(T 3 )-C(T 4 )-*, **—C(T 2 )-C(T 1 )-N—*, **—N—C(T 1 )-N—* and **—N—N—N—*, or Q is one of the following groups which forms an optionally substituted 5 membered heteroaromatic ring, said groups being selected from the group consisting of **—C(T 1 )-N(T 2 )-*, **—C(T 2 )-S—*, **—C(T 2 )-O—*, **—N—N(T 2 )-*, **—N—S—*, **—N—O—*, **—N(T 2 )-C(T 3 )-*, **—S—N—* and **—O—N—*, wherein * indicates a binding site to the carbon atom between the two nitrogen atoms and ** indicates a binding site to the carbon atom substituted by R 1 ; and wherein the symbol “O” in the middle of the ring comprising Q represents the pi-electrons necessary for the aromatic ring; T 1 is one of the groups as defined for R 1 ; T 2 , T 3 and T 4 independently are one of the groups as defined for R 2 ; or wherein one of the groups of T 1 , T 2 , T 3 and T 4 together with one of the groups of R 1 comprise the atoms necessary to form a ring; or wherein one of the groups of T 1 , T 2 , T 3 and T 4 together with one of the groups of R 2 comprise the atoms necessary to form a ring; or wherein two groups, selected from the group consisting of T 1 , T 2 , T 3 and T 4 , comprise the atoms necessary to form a ring.