Effect of Pressure and Radiation on the Luminescent Properties of Poly(vinylbenzophenone−styrene)

Abstract

High-pressure luminescence studies have been made on a polymer with a polystyrene base but with every seventh styrene converted to benzophenone (BP). The polymer was studied neat (PVBS) and in a 10% solution in polystyrene (PVBS-PS). As for BP dissolved in polymers, both photophysical and photochemical effects are observed originating from the triplet state (T 1 ). For PVBS, in addition to the phosphorescence from the monomer, an emission at lower energy occurs which we identify as an excimer and some emission at higher energy identified as delayed fluorescence. In PVBS-PS there is little or no excimer but more intense delayed fluorescence. For PVBS the strongest photophysical effect occurs in the first few kilobar where the excimer intensity increases by a factor of 3-4 at the expense of the monomer phosphorescence. At higher pressure both emissions decrease. For PVBS-PS the phosphorescence (measured on its lowenergy side) shows first a modest increase and then a decrease, analogous to the behavior of BP dissolved in polymers. The delayed fluorescence decreases significantly with increasing pressure. The major effect of irradiation is the dramatic growth of a new emission 4000 cm -1 below the monomer phosphorescence. We attribute this to an emitting photo product much like that observed for BP dissolved in polymers but shifted strongly to lower energy. This occurs in both PVBS and PVBS-PS. The intensity of this emission decreases with increasing pressure. A second effect of irradiation is the strong decrease in the delayed fluorescence, which we attribute to the decreased availability the original phosphorescence for T 1 f S 1 back-feeding.

Pressure-Induced Changes in Crystalline Structures of Polyimides Analyzed by Wide-Angle X-ray Diffraction at High Pressures

“…For perturbing the intermolecular interactions of polymer chains in the solid state, pressure is inherently more ideal than temperature. X-ray diffraction, − infrared absorption (IR) spectra, − UV/vis absorption, and fluorescence spectra − of polymers have been measured under high pressure to examine the compression effects on their crystalline structures and their physical and optical properties. Recently, we reported on the relationship between pressure-induced variations in the molecular aggregation structures and the UV/vis absorption and fluorescence spectra of PIs up to 8 GPa. , Significant variations in the local excitation (LE) and intermolecular CT absorption bands and fluorescence intensity were separately observed for nonfluorescent and highly fluorescent PI films up to 1 GPa.…”

Relationship between Molecular Aggregation Structures and Optical Properties of Polyimide Films Analyzed by Synchrotron Wide-Angle X-ray Diffraction, Infrared Absorption, and UV/Visible Absorption Spectroscopy at Very High Pressure

“…Pressure is a more suitable factor than temperature in perturbing the intermolecular interactions of polymer chains in the solid state. X-ray diffraction, − infrared absorption (IR) spectra, − UV/visible absorption and the fluorescence spectra − of polymers have been measured under high pressure to examine the compression effects on their crystalline structure, and on their physical and optical properties. For instance, Lorenzen et al reported variations in the bulk compressibility of crystalline poly(tetrafluoroethylene) (PTFE) by increasing the pressure using X-ray diffraction patterns.…”

“…Convington et al , measured the pressure-induced shifts of the infrared absorption modes of poly(methyl methacrylate) (PMMA) and polycarbonate (PC), and they concluded that most of the free volume was removed after compression up to 2 and 1 GPa, respectively. Drickermer et al ,, reported variations in the steady-state and time-dependent emission properties of neat polymer and polymer blends. Erskine et al measured pressure-induced variations in the optical transmission spectra of PMDA/ODA PI up to 12 GPa, and concluded that intermolecular CT transitions exist in the PI because a significant bathochromic shift of the absorption edges was caused by applying pressure.…”

Variations in Aggregation Structures and Fluorescence Properties of a Semialiphatic Fluorinated Polyimide Induced by Very High Pressure

“…Pressure is a more ideal external stimulus compared with temperature for perturbing the aggregation structures and intermolecular interactions of polymer chains in the solid state. X-ray diffraction, − infrared (IR) absorption spectra, − and UV/vis absorption and fluorescence spectra − of polymers have been measured under high pressure to examine the compression effects on crystalline and/or amorphous structures and variations in physical properties. For instance, Drickermer et al ,, reported variations in the steady-state and time-dependent fluorescence properties of neat polymer and polymer blends of poly[2-methoxy-5-(2′-ethylhexoxy)- p -phenylenevinylene] (MEH-PPV).…”

“…X-ray diffraction, − infrared (IR) absorption spectra, − and UV/vis absorption and fluorescence spectra − of polymers have been measured under high pressure to examine the compression effects on crystalline and/or amorphous structures and variations in physical properties. For instance, Drickermer et al ,, reported variations in the steady-state and time-dependent fluorescence properties of neat polymer and polymer blends of poly[2-methoxy-5-(2′-ethylhexoxy)- p -phenylenevinylene] (MEH-PPV). Guha et al , observed the fluorescence spectra and Raman scattering of polyfluorene under high pressure.…”