Excimer formation in vinyl polymers. II. Rigid solutions of poly(2-vinylnaphthalene) and polystyrene

Abstract

Excimer formation has been examined in solid films of poly(2-vinylnaphthalene) (P2VN) and polystyrene (PS) as a function of sample temperature from 373 to 4.2°K and film preparation temperature between 373 and 295"K. The concentration of suitable excimer forming sites in the solid state is fixed by the temperature at which the film is cast. A statistical model based on the rotational isomeric state approximation is used to formulate an expression for the fraction of excimer forming sites in the solid systems. This model makes use of the excimer site conformation energy. found to be 2500 cal for P2VN. Excimer sampling in solid solution is shown to be consistent with an activated exciton migration to preformed excimer sites. The mechanism for this process is attributed to a modulation of interchromophore separation resulting from longitudinal acoustical vibrations of the polymer chain. A semianalytical expression for the enhancement of the excitation migration is developed which has the same general form as the experimental results. The effective vibrational frequency is found to be 157 cm-1 for PS and 84 cm-1 for P2VN.

Hexaphenyl Group IVa ethers

“…The crystal structures observed indicate that for these materials a site is available for intermolecular excimer formation without appreciable strain during formation and the spectra are similar to that found in bulk polystyrene (Frank & Harrah, 1974).…”

“…This barrier must arise from necessary configurational changes, in bond angles, and inter-ring separations, which are not required in the carbon-chain analogs (Frank & Harrah, 1974). The influence of these factors on the kinetics of excimer formation and dissociation and on the structure of the excimer state can contribute to the understanding of the formation of the randomly distributed intermolecular excimers found in bulk aromatic polymers (Frank & Harrah, 1974). Previous studies have shown that small misalignment of the principal-axis system of the aromatic chromophores (Chandross & Dempster, 1970) will quench excimer formation but no quantitative data exist relating angular and separation constraints to the excimer-formation process.…”

“…The present materials exhibit both excimer and monomer chromophore fluorescence in solution, indicating a significant barrier to excimer formation even though all rotational conformers are equivalent in these molecules. This barrier must arise from necessary configurational changes, in bond angles, and inter-ring separations, which are not required in the carbon-chain analogs (Frank & Harrah, 1974). The influence of these factors on the kinetics of excimer formation and dissociation and on the structure of the excimer state can contribute to the understanding of the formation of the randomly distributed intermolecular excimers found in bulk aromatic polymers (Frank & Harrah, 1974).…”

“…These changes strongly influence the rates of formation and stabilities of intramolecular excited-state dimers of the phenyl moieties (excimers). Such excimers are generally formed between properly oriented aromatic chromophores in both solids and fluid solutions [for example, in benzene (Birks, Braga & Lumb 1965), pyrene (F6rster & Kasper 1955;Birks, Dyson & Munro, 1963), polystyrene (Vala, Haebig & Rice, 1965), polyvinylcarbazole (K16pffer, 1969, and polyvinylnaphthalene (Frank & Harrah, 1974)]. …”

Interfacial adhesion of nanoparticles in polymer blends by intrinsic fluorescence spectra

“…Thus, the sharp rise in fluorescence intensity should be taken as the signature of phase separation of PS/PVME. For comprehensive understanding of this behavior, the temperature dependence of excimer to monomer fluorescence intensity ratio (I 324 /I 283 ) is also taken into account since excitedstate monomer and excimer can be interconvertible during aggregation of PS [37][38][39]. Obviously, the value of I 324 /I 283 does not change so much and starts to enhance at above 368 K (see Figure 3).…”