High Performance Graded Rainbow Holograms via Two-Stage Sequential Orthogonal Thiol−Click Chemistry

ABSTRACT: Orthogonal, sequential “click ” reactions were implemented to yield novel polymeric substrates with the ability to record holographic data. The base-catalyzed thiol−acrylate Michael “click ” reaction was implemented to yield a writable, stage 1 polymeric substrate with glass transition temperatures (Tg) ranging from 0 to −26 °C and rubbery storage moduli (E′) from 11.1 to 0.3 MPa. The loosely cross-linked matrix also contained a novel high refractive index monomer 9-(2,3-bis(allyloxy)propyl)-9H-carbazole (BAPC) that did not participate in the thiol−Michael reaction but allowed for large index gradients to be developed within the network upon subsequent exposure to coherent laser beams and initiation of the radical-mediated thiol−ene reaction. The holographic gratings were recorded with 96 % diffraction efficiency and ca. 2.4 cm/mJ of light sensitivity in 2 s under a 405 nm exposure with an intensity of 20 mW/cm2. Subsequent to pattern formation, via a thiol−allyl radical “click ” photopolymerization initiated by flood illumination of the sample, holographic materials with high Tg, high modulus, diffraction efficiency as high as 82%, and refractive index modulation of 0.004 were obtained. Graded rainbow holograms that displayed colors from blue to red at a single viewing angle were readily formed through this new technique. 1