A new method to measure molecular weight dependence of intramolecular excimer formation in polymer solutions

The molecular weight dependence of excimer formation efficiency in solution should give important information about polymer photophysics. Each chromophore attached to a polymer molecule is assumed to be in a similar environment independent of the molecular weight. In dilute solution, the chains are isolated. Thus, the variation of molecular weight should provide information about photophysical processes of single chains without introducing a new parameter. Normally, this information is difficult to obtain since one needs a series of samples with a variety of chain lengths, each with narrow molecular weight distribution. Because such samples of polystyrene (PS) are commercially available, most of the experiments reported to date concern this polymer. The chain length dependence of excimer formation has also been examined for solutions of poly(1-vinylnaphthalene) (P1VN), poly(2-vinylnaphthalene), and poly(N-vinylcarbazole). The studies have been less systematic than those on PS. A new simple way is presented to measure the molecular weight dependence of excimer formation efficiency using gel permeation chromatography with tandem fluorescence and differential refractometer detectors. By using this technique and a polymer sample of broad polydispersity, the molecular weight dependence of monomer and excimer fluorescence of P2VN is determined. 23 ref.--AA