Fabrication of refractive index distributions in polymer using a photochemical reaction

Abstract

We demonstrate that a photochemical reaction can create various distributions of refractive index in polymer. When the polymer containing a photochemically active material is irradiated by UV light, the photochemical reaction which breaks the-conjugated system in the material and decreases its linear polarizability can reduce refractive index of the polymer. We prepared a PMMA film added DMAPN ͑͑4-N,N-dimethylaminophenyl͒-NЈ-phenylnitrone͒ with a rate of 23 wt % by use of spin coating. Electronic structural change of DMAPN and refractive indices of the film before and after UV irradiation were evaluated by UV absorption spectra and m-line method, respectively. The UV irradiation decreased max at 380 nm in the absorption spectra, which is attributed to nitrone, and the refractive indices exponentially with irradiation time. The change of refractive indices reached 0.028. The refractive index profile upon depth of the film was investigated by measuring refractive indices of stacked DMAPN/PMMA films. When UV with a power of 10.7 mW/cm 2 irradiated upon three stacked DMAPN/PMMA films for 35 s, variation of the refractive index change showed a quadratic profile. The refractive index profile with various irradiation time can be accounted with the combination of the chemical kinetics with the steady state approximation and Lambert-Beer's law. Thus, the photochemical reaction can be used to control the refractive index distribution in polymer.

Development of Novel Photo-Functional Materials Based on Cyclic Oligomers

“…[10][11][12][13] Nishikubo et al [14][15][16][17] reported that polymers containing certain norbornadiene (NBD) moieties in the main and side chains showed high photochemical reactivity, and had a high photo-energy storage capability. NBD is converted to quadricyclane (QC) under UV irradiation, and the resulting polymers are expected to be good photo-energy transformation systems.…”

“…20 Natansohn et al 21,22 reported that the Án D upon photo-isomerization of polymer films containing azobenzene was about 0.01. Miyata et al 23 reported that 4-N,N-dimethylaminophenyl-N-phenyl nitrone doped in poly-(methyl methacrylate) films showed Án D 's of 0.026-0.028. Sakurai et al [24][25][26][27][28] found that films containing certain nitrone derivatives showed Án D 's of 0.014-0.023 upon photo-isomerization.…”

Molecular Size Effects of Diarylnitrone Additive on the Refractive-Index Change in Poly(methyl methacrylate) Film

“…3 Because the graded index-type POF material thus prepared is much more expensive as compared to standard communication devices, the photocontrol of polymer refractive index, making it possible to provide a simple and economical method for fabricating this type of POF material, has been the subject of extensive research efforts. [4][5][6] Horie and his coworkers showed that photochemical transformations of norbornadienyl 4 and cinnamoyl 5 chromophores incorporated into transparent polymers are both effective for modulating polymer refractive indices. In their studies the refractive index was decreased because of -conjugation greatly weakened by the photoisomerization.…”

“…The modulation of polymer refractive index was achieved also by the photoisomerization of -(4-dimethylaminophenyl)-N 0 -phenylnitrone as an additive to the corresponding oxaziridine derivative. 6 It was concluded that one may generate refractive-index profile for graded index-type POF material by controlling irradiation light intensity and irradiation time.…”

Large Photoinduced Refractive Index Increase in Polymer Films Containing Phenylazide Maintaining Their Transparency and Thermal Stability

“…On the other hands, by using irreversible photochemical reactions such as photoelimination and photopolymerization, large refractive index changes of polymer films have been realized with transparency both before and after photoirradiation in a wide visible region. [10][11][12][13][14][15][16][17][18][19] Among them, Photoelimination brings about the changes not only in electronic structure of photoreactive compounds and also in the density of the polymer films, which leads to larger refractive index changes. 16,17 The refractive indices of the photoirradiated area decreased in many cases, however, the increases in refractive index of the photoirradiated area are necessary for some applications.…”