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

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 (<i>T</i>_g) ranging from 0 to −26 °C and rubbery storage moduli (<i>E</i>′) 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)-9<i>H</i>-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 <i>T</i>_g, 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