Aryl substituent effects on photoinduced refractive index changes were investigated with the use of poly(methyl methacrylate) (PMMA) films doped with (Z)-N-acetyl-a-dehydroarylalanine naphthyl esters ((Z)-1). Upon irradiation with Pyrex-filtered or unfiltered light from a high-pressure mercury lamp, (Z)-1 underwent heterolytic cleavage of the ester C(¼O)-O bond preferentially in both solution and PMMA film to afford arylmethylene-substituted (Z) oxazolone and naphthol derivatives as major products, irrespective of the aryl substituents introduced. Irradiation of (Z)-1 in the film with the unfiltered light enabled much more rapid photochemical transformation into the oxazolones and the intense ultraviolet absorption shifted to longer wavelength relative to that of the starting naphthyl esters. Analysis of the aryl substituent effects confirmed that the PMMA/(Z)-1 system, in which 1-naphthylmethylene-substituted oxazolone was formed along with 1-naphthol, enhanced the refractive index of this polymer film by as much as 0.020.