Generate Rich Fluorescence in a Simple Polystyrene System through Solvent Removal and Molecular Interactions

Abstract

With solvent evaporation, polystyrene fine particles are found to exhibit an unusual fluorescence change from possessing a typical excimer emission band centered at 330 nm to a variety of strong structured bands at longer wavelength with maxima at 356 nm, 365 nm, 372 nm, 383 nm, 404 nm and 426 nm. Similar fluorescence emissions are also observed in polystyrene film after solvent removal. The excitation spectra observed by monitoring these fluorescence emissions at the wavelengths of maxima reveal fluorescence is emitted from different fluorophores. The folding of polystyrene chains during the preparation of polystyrene fine particles through reprecipitation and polystyrene chain relaxation during solvent evaporation are believed to be prerequisites for the formation of different fluorophores via phenyl aggregations, while the aromaticaromatic interactions between the pendant phenyl groups on polystyrene chains are considered to bring a powerful driving force for the formation of fluorophorous phenyl aggregations responsible for the observed fluorescence phenomena. This discovery can contribute to understanding and control of molecular interactions in aromatic systems, especially aromatic macromolecule systems. The luminescence can be used to manufacture light devices and other hybrid materials, as well as to probe local environment in aromatic systems.

Fluorescence Resulting from π-stacking in Polystyrene Solutions

“…1 Fluorescence emission spectra As previously reported by many researchers, Fig.1 demonstrates the fluorescence emissions at λ ex = 260 nm of the studied polystyrene solutions S1, S2, and S3 are centered at the two peaks near 285 and 330 nm which have been assigned to a phenyl monomer singlet and excimer emission, respectively. In the studied polystyrene solutions, the excitation of single phenyl group at 260 nm does not result in the fluorescence emissions in longer wavelengths as observed for the polystyrene fine particles [9] as shown in grey curve.…”

“…However, when excited with 277 nm wavelength light (Fig.2), the polystyrene solutions exhibit fluorescence emissions in longer wavelength region as the polystyrene fine particles [9], but with different emission maxima and fewer structures. The fluorescence emissions of the low concentration polystyrene solutions S2 and S3 are two structureless broad peaks, while the emissions of the high concentration solution S1 show some structured peaks at the same wavelengths observed for the polystyrene fine particles, especially at 347 nm, 355 nm, 365 nm, and 404 nm.…”

“…It has been discussed the fluorescence emissions in longer wavelengths in polystyrene fine particles are emit from the phenyl multimers formed under the driving forces of chain relaxation during solvent evaporation, hydrophobic interactions during reprecipitation and powerful aromatic-aromatic interactions [9] between phenyl groups. Among the three driving forces, only aromatic-aromatic interactions can be applied to the polystyrene solutions.…”

“…The aromatic-aromatic interactions then can overcome the molecular motion and orient the phenyl groups to form phenyl dimers and multimers. Some of these dimers and multimers must be in similar geometries as those formed in polystyrene fine particles, and so that the emission fine structures at longer wavelength side of excimer emission peak at 347 nm, 355 nm, 365 nm, and 404 nm that are observed in polystyrene fine particles [9] are also observed in the S1 solution. The fluorescence emission spectra at λ ex = 277 nm of the studied polystyrene solutions in THF (S1: 0.28 g/ml, S2:1.0×10 -2 g/ml, and S3: 1.2×10 -3 g/ml), compared with the rescaled emission spectrum of the polystyrene fine particles (P1) after vacuum drying [9].…”

“…Recently I reported new structured fluorescence emissions in longer wavelengths (360-460 nm) than polystyrene excimer emission in polystyrene fine particles and cast film [9]. The detailed information about the growth of these new emissions in polystyrene fine particles under ambient conditions and vacuum have also been discussed and documented [10], as well as the energy transfer between different phenyl chromophores: monomers, dimers and multimers.…”