Photo-cleavable perfluoroalkylated copolymers for tailoring quantum dot thin films

Abstract

We report the synthesis, operating mechanism, and application of a copolymer that reveals increasing solubility in fluorous solvents by photolysis. The copolymer, PFBI, was prepared by polymerizing perfluorooctyl methacrylate (FOMA), benzilmonooxime methacrylate (BMOMA) and isobornyl methacrylate (IBMA). It showed a solubility of bigger than 20% (w/v) in a fluorous solvent, 1,1,1,2,3,3-hexafluoro-4-(1,1,2,3,3,3-hexafluoropropoxy)pentane (PF-7600), and the solution could be spin-cast to form 1.5 μm-thick films. When 365 nm UV light was irradiated onto it, 7 μm size stencil patterns could be formed after the UV-exposed regions were washed out with a fluorous solvent of a weaker dissolving power. To verify the responsible chemical mechanism for this increasing solubility, PFBI after UV irradiation was checked by size exclusion chromatography (SEC); no significant molecular weight decrease could be observed. This result suggested that UV exposure may cause the cleavage of the benzilmonooxime moieties, the side units, rather than significant polymer main-chain scission to increase the solubility. As an example of useful applications, PFBI was employed as a stencil material to produce micro-patterned quantum dot (QD) films. After casting a PFBI thin film on a Si substrate, wells for holding the QD ink were formed by UV exposure. After a red QD solution was deposited on the template by spin-coating, the stencil was removed by dissolution in a fluorous solvent, resulting in the 60 μm-sized red QD film arrays. The same steps were repeated with a green QD solution, and two colour QD film arrays could be built successfully. This result demonstrates that PFBI can be applied as a useful patterning material in the organic and printed electronics field.