Two particularly preferred embodiments of P2NNN comprise P2L and P2T, wherein P2L is ##STR37## wherein KB1 is hydrogen, halogen or other group which contains not more than 40 carbon atoms, not more than 24 halogen atoms, and not more than 9 heteroatoms selected from oxygen, nitrogen, silicon, phosphorus and sulfur, this group being optionally connected to KB2 to form an additional ring; and wherei