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The emission properties of poly(2-vinylpyridine) and poly(4-vinylpyridine) (P2VP and P4VP) have been studied in dilute solution in the presence of trifluoroacetic acid (TFA) at room temperature and 77 K. At room temperature, the fluorescence spectra of protonated P2VP exhibit two broad and structureless bands around 325 and 370 nm in addition to the monomer band. On the other hand, the fluorescence spectra of protonated P4VP consist of three broad and structureless bands around 300, 325, and 370 nm, although the dimeric model compound, protonated 1,3-di(4-pyridyl)propane, is not fluorescent. At 77 K, the 325-nm fluorescence band is exclusively observed for both protonated P2VP and P4VP in contrast to the case of the 370-nm fluorescence band. From these observations, the 370-nm fluorescence is ascribed to the emission from a normal excimer that originates from intramolecular interaction between the protonated pyridine chromophores. Furthermore, the 325-nm fluorescence is ascribed to the emission from a dimer-like excimer formed between the protonated pyridine chromophores intramolecularly, whose configuration is different from that of the normal excimer. The favorable conformations for the dimer-like excimer formation are built up in both protonated polymer chains prior to the excitation of the protonated pyridine chromophores. The 300-nm fluorescence (termed monomer-like fluorescence for convenience) seems to be attributable to the emission from the excimer rather than the ground-state dimer. The intramolecular interaction between the protonated pyridine chromophores in the ground state plays an important role in the emission of protonated P4VP. The strong dependence of the dimer-like excimer and the normal excimer formations on the molecular weight of protonated P2VP is related to the molecular motion of the main chain and the protonated pyridine chromophores. This is reflected in the result that the values of the intrinsic association constant and the stacking coefficient for TFA adsorption on the pyridine chromophores increase in the ground state as the molecular weight increases.

The molecular weight dependence of the magnetic circular dichroism (MCD) for polystyrenes (PS) has been studied in various solvents by using the normalized dipole-strength D*. The normalized MCD intensity B* is not so much affected by the molecular weight as the normalized dipole strength D*. The ratio of the Faraday parameter to the dipole strength, B*/D*, decreases as the molecular weight increases to 4,O. lo3 and is constant above it. The increase of the normalized D* with the increase of molecular weight is interpreted in terms of the closer approach of chromophores. These results indicate that MCD for polystyrenes is influenced by the interaction of chromophores in a polymer chain; the decrease of E*/D* comes from the increase of the interaction of chromophores. This tendency is enhanced by solvent effects on MCD.

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