Photochemical fluorescence probes: rate distributions in solid polymers

Non-exponential fluorescence decays due to the photochemical reaction of 10-cyano-9-tert-butyl-anthracene towards the Dewar isomer are analyzed to gain information on the free volume of a polymer glass (poly-n-butyl-methacrylate) at different temperatures. The simple model of a multiexponential fitting procedure is well suited to following the temperature dependence in the envelope of this distribution qualitatively, but it fails to detect finer structures. More demanding methods (maximum entropy and exponential series) result in at least trimodal distributions indicating preferred polymer free volume voids within a broad distribution. Increasing temperature favours the decay time range associated with the largest free volume void.