The properties of the non-fluorescent dye [1-(4-nitrophenyl)-2-pyrrolidinmethyl]-acrylate (NPP-A) have been evaluated with respect to its use in Fluorescence resonant energy transfer (FRET) experiments in polymers. NPP-A is attractive as a FRET-acceptor because its absorption spectrum has good spectral overlap with the emission spectrum of phenanthrene, where the latter is a widely used donor. Importantly, NPP does not fluoresce and therefore does not interfere with time-resolved measurements of the donor fluorescence. The label is well compatible with free radical polymerization. For two polymers, namely (butyl acrylate)-co-(methyl-methacrylate) (50/50) and (butyl methacrylate), the Forster radii were determined from the dependence of the FRET efficiency on the concentration of the acceptor. The results agree within the error. The Forster radius of the phenanthrene-NPP donor-acceptor pair was determined as R-o = 2.47 +/- 0.03 nm. (C) 2007 Elsevier Ltd. All rights reserved.