each L is a single covalent bond, or L is a covalent linkage having 1 24 nonhydrogen atoms selected from the group consisting of C, N, O and S and is composed of any combination of {HEAD ~ single, double, triple or aromatic carbon carbon bonds}, carbon nitrogen bonds, {TAIL ~ nitrogen nitrogen bonds}, carbon oxygen bonds and carbon sulfur bonds; and 
each L is a single covalent bond , or L is a covalent linkage having 1 24 nonhydrogen atoms selected from the group consisting of C , N , O and S and is composed of any combination of { HEAD ~ single , double , triple or aromatic carbon carbon bonds } , carbon nitrogen bonds , { TAIL ~ nitrogen nitrogen bonds } , carbon oxygen bonds and carbon sulfur bonds ; and
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH