Photobleaching of Fluorescent Dyes in Polymer Films

Recently, optical data storage has been achieved via photobleaching of a fluorescent dye in co-extruded, multilayer, polymer films. Photobleaching, the decrease in fluorescence by exposure to light, can be caused by a number of different processes, including light-induced chemical reactions and thermal degradation. Although data has successfully been written using this method, the mechanisms contributing to photobleaching are not fully understood. This project will assist in the understanding of the physics of photobleaching in fluorescent dyes by examining the rate of photobleaching under different temperatures. The fluorescence decay under intense laser illumination is monitored with a home-built light collection and detection system.. The system can be tested using conventional dyes. Fully understanding the details of photobleaching would allow for optimization of the dyes for optical data storage devices. Introduction Optical data storage has been demonstrated in a co-extruded film of poly(ethylene terephthalate glycol) doped with C18-RG. Co-Extrusion Co-Extrusion process: Two polymers are melted together and stacked on top of each other. Each multiplier cuts the stack in half and flows each stack on top of one another. • Fluorescence measured in time. • Sample mounted on an Indium Tin Oxide slide for temperature regulation. • Sample: Rhodamine 6G in SAN25 Results Acknowledgements: Financial support from the NSF Science and Technology Center for Layered Polymeric Systems (Grant 0423914) is gratefully acknowledged. Figure 2: Images taken with confocal microscope of bleached spots in the film. Each square is a separate layer in the film. Figure 1: Film of poly(ethylene terephthalate glycol) doped with C18-RG Figure 3: Diagram of co-extrusion process Figure 5: Example of photobleaching curve with double exponential fit. Figure 4: Confocal microscope setup to measure fluorescence. Excitation light is a BluRay laser diode (405 nm cw). The pinhole blocks diffracted beams from a built in grating. Experiment Figure 7: (Right) Rate constant versus excitation irradiance for two temperatures. At a higher temperature, the bleaching rate increases faster with irradiance. (Left) Examples of bleaching curves for both temperatures at the intensity indicated by the gray oval in the right figure.