Bragg selectivity curves of the transmission gratings recorded on layers containing 1b, 1d and BDPI2 using an exposure energy of 4 J/cm 2 . Shelf-life study has showed unchanged diffraction efficiency for all samples for 4 months (see section 10.4 of the Supporting Information for details). Further shelf-life study is in progress. Refractive index modulation has been estimated by Equation S5 and it has been found to be 2.3 × 10 -3 , 1.5 x 10 -3 and 1.4 × 10 -3 for 1c (74 m thick layer), 1d (87 m thick layer) and BDPI2 (104 m thick layer), respectively. The obtained refractive index modulation is comparable to what was achieved in CA-PEG sensitized with Erythrosine B and NPG as reported in our previous work, and in polyvinyl alcohol-based photopolymers sensitised with Methylene Blue and Erythrosine B 20 (Table ). The grating formation mechanism and creation of the refractive index modulation during holographic recording is discussed in the following section.