The ability of the Fluorescence Blob Model (FBM) to probe the chain dynamics of a polymer backbone was verified for the first time by investigating whether it responds to known differences in backbone flexibility for flexible cis-polyisoprene (PIP) and more sterically hindered polystyrene (PS), both randomly labeled with pyrene. For comparable pyrene contents, the steady-state fluorescence spectra indicated that Py-PIP formed considerably more excimer than the Py-PS samples. Analysis of the fluorescence decays with the FBM provided the rate constant for intramolecular excimer formation. This rate constant was much larger for Py-PIP than for Py-PS, in agreement with the enhanced excimer formation observed for Py-PIP. The enhanced ability of Py-PIP to form excimer is attributed to the PIP backbone being less sterically hindered than the PS backbone. This study is the first example of a comparison of the long range polymer chain dynamics for two different polymeric backbones randomly labeled with pyrene. (C) 2009 Elsevier Ltd. All rights reserved.