chain are independently replaced by a heteroatom selected from the group consisting of o s o 0 2 n and n r 33 the term u201c aryl u201d is intended to mean a mono bi tri or polycyclic c 6 c 14 aromatic moiety preferably comprising one to three aromatic rings preferably the aryl group is a c 6 c 10 aryl group more preferably a c 6 aryl group preferred aryl groups include without limitation phenyl naphthyl anthracenyl and fluorenyl the terms u201c aralkyl u201d or u201c arylalkyl u201d is intended to mean a group comprising an aryl group covalently linked to an alkyl group if an aralkyl group is described as u201c optionally substituted u201d it is intended that either or both of the aryl and alkyl moieties may independently be optionally substituted or unsubstituted preferably the aralkyl group is c 1 c 6 alk c 6 c 10 aryl including without limitation benzyl phenethyl and naphthylmethyl for simplicity when written as u201c arylalkyl u201d this term and terms related thereto is intended to indicate the order of groups in a compound as u201c aryl alkyl u201d similarly u201c alkyl aryl u201d is intended to indicate the order of the groups in a compound as u201c alkyl aryl u201d the terms u201c heterocyclyl u201d u201c heterocyclic u201d or u201c heterocycle u201d are intended to mean a group which is a mono bi or polycyclic structure having from about 3 to about 14 atoms wherein one or more atoms are independently selected from the group consisting of n o and s the ring.