N-substituted pyrrole-2,5-diones having formula: wherein: - R represents a group selected from -OR 1, -NHR 2, -NR 3 R 4, -SO 2 R 5 and -Si(R 6) 3; - Ar represents an aryl group selected from 1-naphthyl and 2-naphthyl, optionally substituted by one or more R" groups; - R 1 represents a group selected from a hydrogen atom, -C R 7, -SO 2 R 8 and -COOR 9; - R 2, R 3 and R 4 independently represent a group selected from C 1 -C 6 alkyl, C 3 -C 6 cycloalkyl, C 1 -C 6 haloalkyl, C 6 -C 12 alkylaryl, -C R 7, -SO 2 R 8 and -COOR 9; - R 5, R 6, R 7, R 8 and R 9 independently represent a group selected from C 1 -C 6 alkyl, C 3 -C 6 cycloalkyl, C 1 -C 6 haloalkyl, C 6 -C 12 aryl, said aryl groups being optionally substituted by one or more groups selected from C 1 -C 6 alkyl or halogen atoms; - R' and R" independently represent one or more groups selected from a hydrogen atom, a halogen atom, C 1 -C 6 alkyl, C 1 -C 6 haloalkyl, C 3 -C 6 -cycloalkyl, C 4 -C 7 - cycloalkylalkyl, C 1 -C 6 -alkoxyl, C 1 -C 6 -haloalkoxyl, C 1 -C 6 -thioalkoxyl, C 1 -C 6 -thiohaloalkoxyl, C 1 -C 6 -alkylsulfinyl, C 1 -C 6 -alkylsulfonyl, C 1 -C 6 -alkoxycarbonyl, C 3 -C 6 -cycloalkoxycarbonyl, amino, N-C 1 -C 6 -alkylamino, N,N-C 2 -C 12 -dialkylamino, N-C 1 -C 6 alkoxycarbonyl-amino, N-C 3 -C 6 -cycloalkylamino, N,N-C 6 -C 12 -dicycloalkylamino, N-C 3 -C 6 -cycloalkoxycarbonyl-amino, C 1 -C 6 -alkylamino-carbonyl, C 3 -C 6 -cycloalkylaminocarbonyl, NR 1 R 2 CONR 1 -, formyl, carboxyl, cyano; excluding compounds wherein: - R is -OSO 2 CH 3, Ar is 1-naphthyl, R' and R" are H; - R is -OSO 2 CF 3, Ar is 1-naphthyl, R' and R" are H; - R is -OH, R' is 3,4,5-OMe, Ar is 2-naphthyl, R" is H. - R represents a group selected from -OR 1, -NHR 2, -NR 3 R 4, -SO 2 R 5 and -Si(R 6) 3; - Ar represents an aryl group selected from 1-naphthyl and 2-naphthyl, optionally substituted by one or more R" groups; - R 1 represents a group selected from a hydrogen atom, -C R 7, -SO 2 R 8 and -COOR 9; - R 2, R 3 and R 4 independently represent a group selected from C 1 -C 6 alkyl, C 3 -C 6 cycloalkyl, C 1 -C 6 haloalkyl, C 6 -C 12 alkylaryl, -C R 7, -SO 2 R 8 and -COOR 9; - R 5, R 6, R 7, R 8 and R 9 independently represent a group selected from C 1 -C 6 alkyl, C 3 -C 6 cycloalkyl, C 1 -C 6 haloalkyl, C 6 -C 12 aryl, said aryl groups being optionally substituted by one or more groups selected from C 1 -C 6 alkyl or halogen atoms; - R' and R" independently represent one or more groups selected from a hydrogen atom, a halogen atom, C 1 -C 6 alkyl, C 1 -C 6 haloalkyl, C 3 -C 6 -cycloalkyl, C 4 -C 7 - cycloalkylalkyl, C 1 -C 6 -alkoxyl, C 1 -C 6 -haloalkoxyl, C 1 -C 6 -thioalkoxyl, C 1 -C 6 -thiohaloalkoxyl, C 1 -C 6 -alkylsulfinyl, C 1 -C 6 -alkylsulfonyl, C 1 -C 6 -alkoxycarbonyl, C 3 -C 6 -cycloalkoxycarbonyl, amino, N-C 1 -C 6 -alkylamino, N,N-C 2 -C 12 -dialkylamino, N-C 1 -C 6 alkoxycarbonyl-amino, N-C 3 -C 6 -cycloalkylamino, N,N-C 6 -C 12 -dicycloalkylamino, N-C 3 -C 6 -cycloalkoxycarbonyl-amino, C 1 -C 6 -alkylamino-carbonyl, C 3 -C 6 -cycloalkylaminocarbonyl, NR 1 R 2 CONR 1 -, formyl, carboxyl, cyano; excluding compounds wherein: - R is -OSO 2 CH 3, Ar is 1-naphthyl, R' and R" are H; - R is -OSO 2 CF 3, Ar is 1-naphthyl, R' and R" are H; - R is -OH, R' is 3,4,5-OMe, Ar is 2-naphthyl, R" is H.