Measuring the size of excitons on isolated phenylene-vinylene chains: From dimers to polymers

Abstract

We have determined the excess polarizability of the relaxed first excited-singlet-state ${S}_{1}$ on isolated chains of phenylene-vinylene oligomers and polymers by measuring the transient change in the microwave dielectric constant that occurs on flash photolysis of dilute solutions. The isotropic value of the excess polarizability volume, $\ensuremath{\Delta}{\ensuremath{\alpha}}^{\ensuremath{'}}{(S}_{1}),$ increases from 250 ${\mathrm{\AA{}}}^{3}$ for a dimer to 960 ${\mathrm{\AA{}}}^{3}$ for an octamer, and 1600 ${\mathrm{\AA{}}}^{3}$ for high molecular weight polymers. The value for the isolated polymer is close to that found for the unrelaxed ${S}_{1}$ state in electroabsorption (Stark effect) measurements on solid samples of poly(phenylene-vinylene), indicating that exciton delocalization is not strongly influenced by either post-excitation relaxation of the polymer backbone geometry, or by interchain interactions.