The fluorescence quantum yield of 9-dicyanovinyljulolidine (DCVJ) is very low in fluid solutions but increases markedly in solids because the medium rigidity slows down the internal motion, which acts as a major nonradiative decay channel. In this work, the excited-state twisting motion of DCVJ in polymers was investigated by time-resolved fluorescence spectroscopy, and it was observed that the fluorescence lifetime of DCVJ in polymers depends on the mechanical properties of the medium. Therefore, our results indicate that the elastic modulus is a determining factor for molecular rotor dynamics in soft matter, and its description requires a comprehensive visco-elasto-plastic theory.