1. A compound having the structure: ##STR7## wherein: X.sup.1 and X.sup.2 are independently selected from H, --NR.sup.2.sub.2, --OR.sup.3, and --CH.sub.2 OR.sup.3 ; or X.sup.1 and X.sup.2 taken together are --OCR.sup.4.sub.2 O--, --OC.sub.2 R.sup.4.sub.4 O--, --OC.sub.2 R.sup.4.sub.2 O--, --N.dbd.CR.sup.5 CR.sup.5 .dbd.N--, --OCR.sup.6 .dbd.N--, .dbd.N--O--N.dbd. or .dbd.N--S--N.dbd. with the proviso that when X.sup.1 and X.sup.2 taken together are .dbd.N--O--N.dbd. or .dbd.N--S--N.dbd. the compound may be represented by the chemical structure; ##STR8## each occurrence of R in the (CR.sub.2) moiety is independently H, halogen, cyano, hydroxy, C.sub.1 -C.sub.6 alkoxy, C.sub.1 -C.sub.3 fluoroalkoxy, thiol, C.sub.1 -C.sub.6 alkyl, C.sub.1 -C.sub.3 fluoroalkyl, C.sub.2 -C.sub.6 alkoxyalkyl, C.sub.6 -C.sub.12 aryl, C.sub.3 -C.sub.12 heteroaryl, C.sub.7 -C.sub.12 arylalkyl, C.sub.4 -C.sub.12 heteroarylalkyl, C.sub.6 -C.sub.12 aryloxy, C.sub.7 -C.sub.12 aryloxyalkyl, C.sub.7 -C.sub.12 arylalkoxy, C.sub.4 -C.sub.12 heteroarylalkoxy, carboxyalkyl, or both R groups together are .dbd.O; each occurrence of R.sup.1 is independently H, C.sub.1 -C.sub.6 alkyl, C.sub.1 -C.sub.3 fluoroalkyl, aryl, heteroaryl, arylalkyl, or heteroarylalkyl; each occurrence of R.sup.2 is independently H, C.sub.1 -C.sub.6 alkyl, C.sub.1 -C.sub.3 fluoroalkyl, C.sub.6 -C.sub.12 aryl, C.sub.3 -C.sub.12 heteroaryl, C.sub.7 -C.sub.12 arylalkyl, C.sub.4 -C.sub.12 heteroarylalkyl, or both R.sup.2 groups together form a carbocyclic ring that includes the nitrogen atom; each occurrence of R.sup.3 is independently H, C.sub.1 -C.sub.6 alkyl, C.sub.1 -C.sub.3 fluoroalkyl, C.sub.2 -C.sub.6 alkoxyalkyl, C.sub.7 -C.sub.12 aryloxyalkyl, C.sub.7 -C.sub.12 arylalkyl, or C.sub.4 -C.sub.12 heteroarylalkyl; each occurrence of R.sup.4 is independently H, halogen, cyano, carboxyalkyl, carboxamido, C.sub.1 -C.sub.6 alkyl, C.sub.1 -C.sub.3 fluoroalkyl, C.sub.2 -C.sub.6 alkoxyalkyl, C.sub.7 -C.sub.12 aryloxyalkyl, C.sub.7 -C.sub.12 arylalkyl, or C.sub.4 -C.sub.12 heteroarylalkyl; each occurrence of R.sup.5 is independently H, cyano, hydroxy, C.sub.1 -C.sub.6 alkoxy, C.sub.1 -C.sub.6 alkyl, C.sub.1 -C.sub.3 fluoroalkyl, C.sub.2 -C.sub.6 alkoxyalkyl, or C.sub.7 -C.sub.12 arylalkyl, C.sub.4 -C.sub.12 heteroarylalkyl, C.sub.6 -C.sub.12 aryloxy, C.sub.7 -C.sub.12 aryloxyalkyl, C.sub.7 -C.sub.12 arylalkoxy, or C.sub.4 -C.sub.12 heteroarylalkoxy; each occurrence of R.sup.6 is independently H, C.sub.1 -C.sub.6 alkyl, C.sub.1 -C.sub.3 fluoroalkyl, C.sub.7 -C.sub.12 arylalkyl or C.sub.4 -C.sub.12 heteroarylalkyl; Z is O or S and n is 1, 2, 3, or 4.