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

Abstract

ABSTRACT:We realized large photoinduced refractive index increases of poly(methyl methacrylate) (PMMA) films containing phenylazide (PAZ) through photochemical and thermal processes. The refractive index increase of the PMMA film containing 30 wt% PAZ through the processes is as much as 0.0161 with transparency in a wide visible region both before and after photoirradiation and with moderate thermal stability. These excellent performances suggest the applicability of PAZ doped PMMA films for optical devices.KEY WORDS Refractive Index Increase / Photocleavage / Phenylazide / M-line Method / Polymer Film / Poly(methyl methacrylate) (PMMA) / Nitrene / Optical Device / Organic polymers have received considerable attention as materials for opto-electronics applications because of their processability and reasonable cost performances. Some organic polymers have already been applied to optical devices, such as optical fibers, microlenses, liquid crystal display components and polymer light emitting diodes. 1, 2 The possibility of organic polymers for opto-electronics applications is not limited, and developments of organic polymers have been more and more promoted.A photochemical reaction is an important process in the fabrication of refractive index patterns in polymer films. The photochemical reaction can induce larger refractive index modulation in polymer films and the modulation remains after the photoreaction, leading to the permanent change in refractive index. Therefore, photochemically induced refractive index changes in polymer films have been attracting much attention for various applications, such as optical memories, switching devices and optical waveguides.We can use various kinds of photoreactions, such as photoisomerization, photodimerization, photoelimination, and photopolymerization. These reactions bring about the changes in electronic structure of photoreactive compounds, which result in the refractive index changes of polymer films. Photoisomerization of photochromic compounds is one of the attractive candidates for making refractive index patterns in polymer films reversibly. 3-9 However many photochromic compounds become colored after photoisomerization with absorption bands in the visible region, which may disturb the transmittance of probing light in optical † To whom correspondence should be addressed.devices. 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 appli...

Development of Novel Photo-Functional Materials Based on Cyclic Oligomers

“…Toussaere et al 31 reported that the photo-chemical isomerization of thiocyanate moieties under photo-irradiation; the Án D reached about 0.03. Horie et al 32 examined films doped with phenylazide and found an Án D after photoirradiation of 0.0161. Kern et al 33,34 examined the photo-Fries rearrangement based on the polymer, and observed Án D 's in the range from 0.042 to 0.070.…”

“…Two isosbestic points at 235 and 249 nm were observed; this suggests that the photochemical isomerization of calixarene derivatives occurred selectively without any side reaction upon photo-irradiation. A linear relationship 31 Horie et al 32 Sakurai et al 35 ∆n D = + 0.030…”

Effects of aryl substituents in N-acetyl-α-dehydroarylalanine naphthyl ester additive on the photoinduced refractive index change of poly(methyl methacrylate) film

“…An additional increase in refractive index was observed upon treating the polymer with hydrazine (refractive index change, Dn¼+0.035). Murase et al 23 also showed that photochemical and thermal treatments of poly(methyl methacrylate) (PMMA) film doped with 30 wt% of phenyl azide raised the index of this film by 0.016. In addition, the photo-Fries rearrangement in polymers bearing aromatic ester pendants was found to cause a large increase in refractive index for these polymer films (Dn¼+0.03À(+0.07)).…”

“…3 Although there are extensive studies directed toward a photoinduced decrease in refractive indices for polymer films, [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] only a few attempts have been made to enhance the refractive index through photochemical transformations. 12,[20][21][22][23][24][25] For example, Langer et al 21 reported that irradiation of a polymerbearing thiocyanate pendants enhanced the refractive index (n) of the polymer by 0.031. An additional increase in refractive index was observed upon treating the polymer with hydrazine (refractive index change, Dn¼+0.035).…”

Novel Refractive Index Increase Material Based on Polystyrenes with Pendant Bicyclo Orthoester Groups upon Photoirradiation

“…Toussaere et al 21 reported that photochemical isomerization of thiocyanate moieties resulted in Δn D of about þ0.03. Horie et al 22 examined thin films doped with phenylazide and observed Δn D after photoirradiation of þ0.0161. Sakurai et al 23 reported that n D of thin film doped with N-acetyl-R-dehydroarylalanine naphthyl ester increased by about þ0.02 after photoirradiation.…”