Here, we aim to systematically examine the mechanism of photo-induced pyrene association in pyrene-labeled polymers (PLPs) for optical recording. By taking advantage of polymer glass transition, the associated pyrene moieties can be frozen in the glassy matrix of the PLP to give the emission contrast for optical recording, as evidenced by the phenomenon of room-temperature phosphorescence. In situ time profiles of the fluorescence emission during recording reflect that the association of pyrene moieties in PLPs is a diffusion-controlled process, and it is highly dependent on the mobility of the polymer chain. For crystallizable PLPs, the polymer chain can also be frozen in the crystalline state that inhibits the association of pyrene moieties in PLPs. As a result, Tg and Tm of the PLPs can be exploited as energy barriers for the induction of the association of pyrene moieties in PLPs and the recording capabilities of the PLPs will be dependent upon the thermal properties of the PLPs.