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

We have determined the excess polarizability of the relaxed first excited-s inglet-state S-1 on isolated chains of phenylene-vinylene oligomers and pol ymers by measuring the transient change in the microwave dielechic constant that occurs on flash photolysis of dilute solutions. The isotropic value o f the excess polarizability volume, Delta alpha'(S-1), increases from 250 A ngstrom(3) for a dimer to 960 Angstrom(3) for an octamer, and 1600 Angstrom (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 (St ark effect) measurements on solid samples of poly(phenylene-vinylene), indi cating that exciton delocalization is not strongly influenced by either pos t-excitation relaxation of the polymer backbone geometry, or by interchain interactions.