The objective of this investigation was to develop stable nonlinear optical (NLO) Materials which possess both second and third order NLO properties. These Materials were envisioned as having a polydiacetylene (PDA) backbone with a second order active NLO chromophoric substituent consisting of a donor group, a π-conjugated bridge, and an acceptor group. The choice of a PDA backbone in this investigation was twofold. In terms of third order NLO properties, the extensive π-conjugation of the PDA backbone leads to large ultrafast third order effects. In terms of second order NLO properties, the high thermal stability and rigidity of the PDA Matrix in a perfect polymeric single crystal is expected to prevent the randomization of the NLO chromophores in the noncentrosymmetric environment. This paper focuses on the synthesis and NLO properties of the unsymmetrical diacetylene Monomers, ((9-Butoxy carbonyl) Methyl urethanyl) -l- (4-urethanyl-4'-nitrobiphenyl) -nona-2,4-diyne, and ((9-Butoxy carbonyl) Methyl urethanyl) -l- (4-urethanyl-4'-nitroazobenzene) -nona-2,4-diyne. The high entropy flexible urethanyl side group was chosen to satisfy the monomer packing requirements for polymerization and enhance the solubility of the PDAs.