, especially ???NHCH3 or ???N(CH3)2, ???COR11, especially ???COCH3, or ???N(R12)COR11, especially ???NHCOCH3, group.Particularly useful Ar groups in compounds of formula (1) include phenyl and mono- or disubstituted phenyl groups in which each substituent is in particular a ???R10a or -L6Alk5(R10a)r atom or group as just defined and is especially a halogen atom or a C1-3 alkyl, C1-3 alkoxy or ???C