wherein Z.sup.1 is (CH.sub.2).sub.q or C.dbd.O; Z.sup.2 is (CH.sub.2).sub.p or C.dbd.O; D is --CH.dbd. or C.dbd.O or (CH.sub.2).sub.m where m is 0, 1, 2 or 3; n=0, 1 or 2; p=1 or 2; q=0, 1 or 2; Q is C or N; A is (CH.sub.2).sub.x where x is 1 to 5, or A is (CH.sub.2).sub.x.sup.1, where x.sup.1 is 1 to 5 with an alkenyl bond or an alkynyl bond embedded anywhere in the chain, or A is --(CH.sub.2).sub.x.sup.2--O--(CH.sub.2).sub.x.sup.3-- where x.sup.2 is 0 to 5 and x.sup.3 is 0 to 5, provided that at least one of x.sup.2 and x.sup.3 is other than 0; B is a bond or is (CH.sub.2).sub.x.sup.4 where x.sup.4 is 1 to 5; X is CH or N; X.sub.2 is C, N, O or S; X.sub.3 is C, N, O or S; X.sub.4 is C, N, O or S; X.sub.5 is C, N, O or S; X.sub.6 is C, N, O or S; provided that at least one of X.sub.2, X.sub.3, X.sub.4 X.sub.5 and X.sub.6 is N; and at least one of X.sub.2, X.sub.3, X.sub.4 X.sub.5 and X.sub.6 is C. R.sup.1 is H or alkyl; R.sup.2 is H, alkyl, alkoxy, halogen, amino, substituted amino or cyano; R.sup.2a, R.sup.2b and R.sup.2c may be the same or different and are selected from H, alkyl, alkoxy, halogen, amino, substituted amino or cyano; and R.sup.3, E, Z and Y are as defined herein.