In this work, thermal transitions of polystyrene, PS, were studied as a function of molecular weight (M,,) and thermal history using the fluorescence response of anthracene chemically bonded to the polymer chain ends. For each PS sample the fluorescence spectra of the anthracene were collected as a function of temperature in cycles of heating and cooling. Two photophysical parameters were selected in order to study thermal transitions of the PS samples: (i) the first moment of the fluorescence band, &LANGBRAC; v&RANGBRAC;; and (ii) the integrated fluorescence intensity, I. In every case, a sharp change in the photophysical parameter was observed at a certain temperature that was assigned to the a relaxation temperature and which was clearly different depending on the PS molecular weight and the thermal history. In fact, the relaxation temperature increased with M-w during a heating scan, decreased with Mw during a cooling scan and was clearly lower in the cooling scans. These results were interpreted in terms of a reorientation of the anthryl groups to the surface of the polymer. © 2005 Elsevier Ltd. All rights reserved.