Compounds of the following formula are disclosed: ##STR00001## wherein R.sup.B is a substituted or unsubstituted aryl or heteroaryl moiety; at least one of R.sup.U and R.sup.L is a phosphorus-containing moiety, J, and the other of R.sup.U and R.sup.L is independently chosen from H; halogen; --CN; --NO.sub.2; -J; --SO.sub.2R; --SO.sub.2NRR'; or --ZR.sup.J, wherein each occurrence of Z is independently --O--, --S-- or --NR-- and each occurrence of R.sup.J is independently --R, --COR, --COOR or --CONRR'.