A vapor-deposited thin film of N-[4’-(5’-hydroxypenta-1 ",3 "-diynyl)-benzylidene]-4-octyloxyaniline, which is one of the diacetylene compounds, demonstrated a drastic change of its electronic absorption spectrum characterized by the absorption edge being expanded to the near-infrared region, associated with heating its substrate above 100 degrees C. X-ray diffraction patterns of the film revealed that there are three different stages for the film at temperatures elevated through heating. As it has been confirmed that the molecule concerned suffers no chemical change through the heat treatments, those observed phenomena can be understood to be induced by a characteristic change in intermolecular electronic interaction via modification of molecular aggregation forms caused by substrate heating.