A Photoinduced Refractive Index Increase in Poly(methyl methacrylate) Film Doped withN-Acetyl-α-dehydroarylalanine Naphthyl Esters

Abstract

As a result of great demand for advanced optical materials such as plastic optical fiber, 1 the photochemical decrease in refractive index for polymer films has attracted considerable attention for the past decade. [2][3][4] We succeeded in lowering the refractive index of poly-(methyl methacrylate) (PMMA) film (doped with hydroxy-substituted diarylnitrones) by as much as 0.014 (-∆n) by their quantitative photochemical conversions into diarylformamides showing a much weaker π-conjugation. 3 On the other hand, there are only a few studies directed toward the photochemical increase in refractive index for a given polymer film. [6][7][8][9][10] reported that the photoirradiation of polymers bearing thiocyanate pendants enhances the polymer refractive index by 0.031; an additional increase in refractive index is observed upon treating the polymer with hydrazine (∆n ) +0.035). Murase et al. 7 also showed that the 3 h photochemical and 3 h thermal treatments of PMMA film doped with 30 wt % of phenyl azide raise the index of this film by 0.0161. While the refractive index changes described above seem to be sufficient magnitude for utilizing these polymers as optical materials, it is necessary to increase the stability of polymer refractive index and also to speed up the photochemical transformation being responsible for the refractive index change of a given polymer film.In the course of our systematic study regarding the excited-state reactivities of N-acyl-R-dehydroarylalanines, it was found that (Z)-N-acetyl-R-dehydrophenylalanine aryl ester derivatives in the singlet excited state undergo the heterolytic cleavage of the ester C(dO)-O bond to eventually form the corresponding oxazolones and aryl alcohols by way of the cyclization of acylinium intermediates (Scheme 1). 11 In contrast to the photoisomerization of diarylnitrone derivatives, the photoheterolysis of dehydrophenylalanine aryl esters gave oxazolones as one of the major products, the absorption of which appeared on the much longer wavelength side than that of the aryl esters. Thus, the novel photochemical transformation of these esters into oxazolones results in an enhancement in the π-conjugation, namely, the linear polarizability of given molecules, which allows us to propose that this photoreaction is accompanied by an increase in refractive index. In this Communication we present the results which demonstrate that the short period of time irradiation of PMMA film doped with N-acetyl-R-dehydrophenylalanine 1-naphthyl ester (1a) or N-acetyl-R-dehydro(1-naphthyl)alanine 1-naphthyl ester (1b) increases the refractive index of this polymer film greatly, and then our refractive index photocontrol system enables application to new optical materials.The starting (Z)-isomers of 1a and 1b were prepared by the ring-opening reactions of (Z)-2-methyl-4-(benzylidene)-5(4H)-oxazolone (2a) and (Z)-2-methyl-4-(1-naphthylmethylene)-5(4H)-oxazolone (2b) with 1-naphthol in dry chloroform containing triethylamine, respectively. 12,13 In Figure 1 are typically shown UV absorp...

Development of Novel Photo-Functional Materials Based on Cyclic Oligomers

“…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. Sakurai et al 35 reported that Án D of poly(methyl methacrylate) film doped with N-acetyl--dehydroarylalanine naphthyl ester reached about 0.02. However, it is difficult to apply these materials in the optoelectronics industry, because the photo-chemical reaction is accompanied with release of low-molecular compounds or gases.…”

“…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…”

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

“…Horie et al examined thin films doped with phenylazide and observed Δ n D after photoirradiation of +0.0161. Sakurai et al reported that n D of thin film doped with N -acetyl-α-dehydroarylalanine naphthyl ester increased by about +0.02 after photoirradiation. Very recently, Kern et al , recently examined the photo-Fries rearrangement of polymer and found Δ n D values in the range between +0.042 and +0.070.…”