The effect of nanoscale confinement on the glass transition temperature, T-g, of freely standing polystyrene (PS) films was determined using the temperature dependence of a fluorescence intensity ratio associated with pyrene dye labeled to the polymer. The ratio of the intensity of the third fluorescence peak to that of the first fluorescence peak in 1-pyrenylmethyl methacrylate-labeled PS (MApyrene-labeled PS) decreased with decreasing temperature, and the intersection of the linear temperature dependences in the rubbery and glassy states yielded the measurement of T-g. The sensitivity of this method to T-g was also shown in bulk, supported PS and poly(isobutyl methacrylate) films. With free-standing PS films, a strong effect of confinement on T-g was evident at thicknesses less than 80-90 nm. For MApyrene-labeled PS with M-n = 701 kg mol(-1), a 41-nm-thick film exhibited a 47 K reduction in T-g relative to bulk PS. A strong molecular weight dependence of the T-g-confinement effect was also observed, with a 65-nm-thick free-standing film exhibiting a reduction in T-g relative to bulk PS of 19 K with M-n = 701 kg mol(-1) and 31 K with M-n = 1460 kg mol(-1). The data are in reasonable agreement with results of Forrest, Dalnoki-Veress, and Dutcher who performed the seminal studies on T-g-confinement effects in free-standing PS films. The utility of self-referencing fluorescence for novel studies of confinement effects in free-standing films is discussed. (C) 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2754-2764, 2008