Donal Bradley

Abstract:

For any polymer the determination of the average molecular weight and its distribution is an important part of characterizing its physical properties. We report values for the M̄n, M̄w and dispersity, determined using gel permeation chromatography, of a neutral precursor polymer to poly(p-phenylenevinylene) in relation to polymerization conditions. We have observed a maximum M̄n value of approximately 100,000 with a dispersity of 5.7 and compare this value to that calculated for the `effective conjugation length', that is the number of repeat units over which uninterrupted π-electron delocalization actually takes place, in fully converted poly(p-phenylenevinylene).

Abstract:

We have developed a synthetic method that allows a controlled increase in the one-dimensional character of poly(p-phenylenevinylene) by subtle chemical modification of the precursor polymer. Examples of the unoriented fully conjugated material exhibit room temperature optical absorption spectra (uncorrected for reflectivity) which have a peak in absorption at 2.45 eV with subsidiary shoulders at higher photon energies. The absorption maximum is red-shifted with respect to previously observed values. Luminescence spectra of these samples recorded at 10K are complementary with a peak in emission at 2.38 eV and accompanying subsidiary maxima at lower energies. The peaks in absorption and emission are identified as the transitions between the vibrational ground states of the electronic and the first excited singlet states which we term the (0,0) transitions.