Holographic photopolymerizable glass: Enhancing exposure sensitivity by tailoring photoinitiating systems based on BODIPY dyes

The photoinitiating system (PIS) is a key component of holographic materials which needs to be carefully selected and optimized to achieve efficient photopolymerization and, as a result, highly efficient holographic structures. Recently, boron dipyrromethene (BODIPY) dyes have been introduced as a new class of photosensitizers for holographic materials, including photopolymerizable glass, which is characterized by excellent environmental stability. Here, we present a study of the holographic recording capability of the photopolymerizable glass, where PIS was optimized using two approaches: 1) adding a second co-initiator, diphenyl iodonium hexafluorophosphate (DPIHFP) and 2) exploring a range of BODIPY structures, such as anthracene- and pyrene-BODIPYs. The performance of the novel pyrene-BODIPY dyad was compared with commercially available Erythrosine B, used as a reference. Remarkably, 9-fold increase in the diffraction efficiency and refractive index modulation (RIM) was achieved by replacing Erythrosine B with pyrene-BODIPY dyads, indicating enhanced photopolymerization kinetics with BODIPY sensitization. In addition, incorporating the second co-initiator, DPIHFP, further increases the exposure sensitivity by a factor of three. These results demonstrate the high efficiency of BODIPY-based PIS formulations and underscore photopolymerizable glass as a promising platform for developing highly efficient holographic optical elements.