For the past half-century, a number of polyesters have been used for application in textile and film manufacturing. Currently, the polyester R&D effort directed toward advanced materials involves further progress in the synthesis given by a wide range of potential monomer combinations, new blending technology, and the use of advanced functional additives. As one such effort, we developed a facile modulation method to afford unique photophysical properties to an aliphatic polyester film. For this purpose, a free-standing film based on a network aliphatic polyester consisting of malonate moiety was successfully prepared. The UV-vis, IR, and photoluminescence studies revealed that the prepolymer underwent a Knoevenagel-type self-condensation in situ in the solid film via thermally reactive processing, leading to formation of certain conjugating structures in the polymer chain: The film showed an apparent change from colorless to pale yellow by thermal treatment at 240 ° C and then emitted a very intense greenish-blue light when excited at wavelengths longer than 325 nm, The characteristic IR absorption peak at 1654 cm(-1), due to the carbon-carbon double bond, appeared and gradually increased with increasing the heating time, whereas the absorptions due to the methylene and carbonyl groups slowly decreased. The thermally treated film was completely homogeneous at the micrometer level without such defects as decomposition and aggregation. The film showed excellent mechanical properties, relatively high density, and thermal stability. In addition, the prepolymer had excellent processability, due to the high adhesiveness, to afford pinholes and thin-line films with several micrometer features.