Disclosed herein are polydiphenyldiacetylenes having the following repeating unit (III): ##STR1## (wherein R.sup.1 denotes a hydrogen atom or a methoxy group; R.sup.2 denotes a hydrogen atom, a methoxy group or a methylamino group; R.sup.3 denotes a hydrogen atom or a trifluoromethyl group; and R.sup.4 denotes a hydrogen atom or a trifluoromethyl group; provided that R.sup.1 is not a hydrogen atom when R.sup.2 is hydrogen atom, and R.sup.3 is not a hydrogen atom when R.sup.4 is hydrogen atom).
Diphenyldiacetylene derivatives represented by the following formula (II);
(wherein R¹ denotes a hydrogen atom or a methoxy group; R² denotes a hydrogen atom, a methoxy group or a methylamino group; R³ denotes a hydrogen atom or a trifluoromethyl group; and R⁴ denotes a hydrogen atom or a trifluoromethyl group; provided that R¹ is not a hydrogen atom when R² is hydrogen atom and R³ is not a hydrogen atom when R⁴ is hydrogen atom) are capable of exhibiting a non-linear optical effect and can be polymerized in the solid state to form non-linear optical materials, photosensitive materials and semiconductive polymer materials.