Knowledge Bank

The fluorescence spectra of fluid and glassy solutions of poly (2-vinyl naphthalene) (PVN) have been studied at temperatures from $77\circ K$ to $350\circ K$. Excimer emission is observed at all temperatures in glassy solutions and the relative intensity, excimer to monomer unit, of fluorescence is characteristic of the temperature at which the glass if formed. In fluid solution the ratio of excimer to monomer unit fluorescence depends only on the observing temperature. This behavior is interpreted in terms of excimer forming main chain sites which are of higher energy than the most stable chain conformation. In fluid solution these conformations are collisionally sampled through internal rotation of the chain with an experimental barrier height to internal rotation of $\approx 3600$ cal/mole. In the glassy state the excimer forming sites are frozen in and the casting temperature dependence indicates an energy difference for site formation of $\approx 2400$ cal/mole. Excimer formation in the glassy solutions results from intrachain exciton migration to these ``frozen in’’ sites with subsequent trapping and excimer fluorescence. This work was supported by the U. S. Atomic Energy Commission.