Naphthalene-and pyrene-labeled polymers (poly-3-5) prepared by group transfer polymerization of methyl 2-(2-naphthyl)acrylate, methyl 2-(1-pyrenyl)acrylate, and ethyl 5-(2-naphthyl)pentadienoate and ethyl 5-(2-naphthyl)hexadienoate, respectively, were studied as probes for backbone conformational rigidity. Excimer formation was observed in the steady-state fluorescence spectra, and the observation of biexponential decay of time-resolved fluorescence indicates two distinct environments for excimer formation. These, in turn, point to substantial conformational flexibility in the polymer backbone.