Fluorescence probes for polymer free-volume

Abstract

A series of fluorescence Probes (p-(N, N-dialkylamino) benzylidene malononitriles) which belong to a class of organic compounds known as “molecular rotors” has been developed. The internal molecular rotation of these compounds can be slowed down by increasing the surrounding media rigidity, viscosity or decreasing the free-volume available for molecular relaxation. Inhibition of internal molecular rotation of the probe leads to a decrease in the non-radiative decay rate and consequently enhancement of fluorescence. Therefore, the fluorescence emission of this class of compounds allowed us to study both the static and dynamic changes in free-volume of polymers as a function of polymerization reaction parameters, molecular weight, stereoregularity, crosslinking, polymer chain relaxation and flexibility. In addition, the dependence of the fluorescence emission maximum of these probes on media polarity allow continuous monitoring of the probes location in the polymer matrix. Therefore, these fluorescence materials are capable of simultaneously probing the flexibility and polarity of the surrounding media. © 1986 IUPAC