Naphthylmethylammonium salts of a series of diacetylene-containing carboxylic acids with various sizes of alkyl chains were photopolymerized in the crystalline state. X-ray crystal structure analyses confirmed lamellar structures characterized with the two-dimensional hydrogen networks formed between carboxylate anion and countercation layers in the crystals. The absorption properties of the resulting polymers depended on the length of alkyl substituents.