Singlet Oxygen Images of Heterogeneous Samples:  Examining the Effect of Singlet Oxygen Diffusion across the Interfacial Boundary in Phase-Separated Liquids and Polymers

Abstract

Optical images of glassy, phase-separated polymer films have been generated using the 1270 nm phosphorescence of singlet molecular oxygen. Specifically, upon irradiation of immiscible blends of polystyrene and poly(ethylene-co-norbornene) that contain a singlet oxygen sensitizer, phase-separated droplets as small as ∼10 μm in diameter could be resolved using a microscope designed to detect singlet oxygen phosphorescence. This study demonstrates that it is possible to create singlet oxygen images of systems in which the sensitizer is not mobile (i.e., systems in which the effects of sensitizer bleaching cannot be rectified by diffusion of more dye into a given volume). The effect of singlet oxygen diffusion across the interfacial boundary between phase-separated domains of both liquid and polymer samples has also been examined. For singlet oxygen created in one phase, diffusion into a second phase in which the quantum yield of singlet oxygen phosphorescence is larger and oxygen is more soluble gives rise to a significant change in the intensity of the singlet oxygen signal at the interface. This effect can be pronounced when a long singlet oxygen lifetime facilitates singlet oxygen diffusion over large distances, but can be mitigated when interfacial tension yields a phase boundary with appreciable curvature. Boundary curvature in thin, phase-separated films of polystyrene/poly(ethylene-co-norbornene) is slight. Moreover, the singlet oxygen lifetime in these polymers is sufficiently short that, within its lifetime, singlet oxygen cannot diffuse over an appreciable distance. Under such conditions, singlet oxygen images of interfacial boundaries are sufficiently sharp as to make this optical technique useful for a range of fundamental studies.

Photosensitisation studies of silicone polymer doped with methylene blue and nanogold for antimicrobial applications

“…27 For polysiloxane polymers using a value for the diffusion coefficient D ¼ 10 À6 cm 2 s À1 at 300 K the average diffusion distance is <0.1 mm [root-mean-square linear displacement] $ [(2s D D) 1/2 ]. 60 ms. For example the average distance travelled by 1 O 2 in D 2 O over 65 ms is approximately 0.62 mm.…”

5,10,15,20-Tetrakis(N-Methyl-4-Pyridyl)-21H,23H-Porphine (TMPyP) as a Sensitizer for Singlet Oxygen Imaging in Cells: Characterizing the Irradiation-dependent Behavior of TMPyP in a Single Cell†

“…The basic features of the instrumentation and methods employed in the present study have been described previously (21, 34–36). Briefly, singlet oxygen was generated in a photosensitized process upon irradiation of TMPyP incorporated in the sample of interest.…”

Two‐Photon Singlet Oxygen Microscopy: The Challenges of Working with Single Cells

“…Of course, in solvents where the O 2 (a 1 Δ g ) lifetime is longer, the diffusion distance d will be correspondingly larger. In the long run, this must be kept in mind when working with inhomogeneous samples where oxygen diffusion from one solvent domain into another could influence the intensity of the measured signal (35).…”