Large Photoinduced Refractive Index Change of Polymer Films Containing and Bearing Norbornadiene Groups and Its Application to Submicron-Scale Refractive-Index Patterning

Abstract

We measured photoinduced refractive index changes of polymer films containing various norbornadiene compounds. Poly(methyl methacrylate) (PMMA) films containing 51.6 wt% of 5,6-(2-benzofuryl)-2,3-di(trifluoromethyl)-1,4,7,7-tetramethyl-2,5-norbornadiene (NBD4) showed refractive index changes of 0.037 during photoisomerization. A polymer film bearing thiophenyl- and benzofuryl- substituted norbornadiene groups (PolyTBFNBD) showed a refractive index change of 0.05–0.06 for 594–632.8 nm during photoisomerization. This value is the largest value of refractive index change so far in a nonresonant region induced by photochemical reactions. Submicron-scale patterning of pure refractive-index contrast on the PolyTBFNBD film was also demonstrated by using near-field scanning optical microscopy (NSOM).