We describe an unusual temperature dependence of 1,8-diphenyl-1,3,5,7-octatetraene absorption in poly(vinyl alcohol) films. Upon heating above 80 °C, the optical density (in the long wavelength region) of this compound increases rapidly. A sample heated to 150 °C has a nearly twenty times higher optical density than a non-heated sample. This effect is not reversible: Once the sample is heated it retains its absorbance on cooling to room temperature. In our opinion, the effect has its origin in changes of the chromophore molecules from cis to trans conformation at the high temperature. Possible applications of these unique material properties should be improved temperature sensors, optical data storage, non-developed high resolution photography or typing, etc.