Symmetrically substituted 1,3-diynes, X(CH2)nC?C - C?C(CH2)nX (X = Et2N; n = 4, 9; 1d,e) have been prepared from the appropriate bis-tosylates (X = OSO2C6H4Me-p; 1b,c) and diethylamine, and one such derivative has been converted into a bis-quaternary ammonium salt (X = N+Et2MeI-; n = 4; 1f) and an ammonium sulfonate inner salt (X = N+Et2(CH2)3SO3-; n = 4; 1g), respectively. Three bis-phosphonium salts, X(CH2)nC?C - C?C(CH2)nX (X = P+Ph3Br-; n = 4, 9, 3; 1h-j), were synthesized from 1,4-bis(bromoalkyl)-1,3-diynes and the appropriate phosphine derivative. The new diyne derivatives did not polymerize on exposure to ?-irradiation or electron beam irradiation in a Van der Graff linear accelerator. The tosylated polydiacetylene (PDA) derivative (2a, 'PTS-12') derived from 1b was treated with diethylamine to yield a tertiary amine-functionalized PDA derivative (2b), and the latter was allowed to react (separately) with methyl iodide and 1,3-propanesultone to give ionomeric PDAs 2c and 2d, respectively. The phosphinated PDA (2e) was synthesized from PTS-12 (2a) and diphenylphosphinyl-lithium or -potassium, and this material was used to prepare the PDA phosphonium salt 2f. The nonlinear optical properties of selected new PDAs (2c,d,f), as well as some known PDAs, were evaluated by means of the z-scan technique. The magnitudes of two-photon absorption coefficients (ß) were determined and are discussed.