Photo-Induced Self-Condensation, A Technique For Fabricating Organic Lightguide Structures

Photoinduced condensation of sol-gel hybrid glass films doped with benzildimethylketal

“…In the present study, there was no absorption peak at 380 nm that would be caused by the benzil molecule. 13 The benzil molecule is also photosensitive and undergoes further photochemical reaction during UV illumination. Therefore, the coupling effect of the benzoyl radicals may be neglected in BDK-doped SGHG.…”

“…This transition is followed by an ␣-splitting. 13 If BDK is photodecomposed to two radicals, they can initiate polymerization or make a new molecule by the coupling of two benzoyl radicals. 12 Detailed schemes of BDK photochemical reactions are represented in Fig.…”

“…Actually, it was found that the radicals produced by photodecomposition of BDK are locked or fixed in polymers to increase the refractive index while BDK is very mobile to diffuse out during baking of the polymers. 12,13 To monitor the photodecomposition of BDK, the UV absorptions of the films were examined depending on the UV illumination time. When BDK is irradiated by UV light, it is activated by an n(sp) → M* transition within the molecular orbits of the >C‫ס‬O group.…”

“…Because BDK in the unexposed film is not photodecomposed, BDK can be removed during baking, which was already found in previous studies. 12,13 Thus, the unexposed film with higher BDK concentration may be less dense than that with lower BDK resulting in reduction of the refractive index. However, the higher refractive index is obtained for the UV illuminated film, as BDK concentration is larger.…”

“…In addition to photoinitiating characteristics, BDK has been used in fabrication of polymer waveguides, because it can increase the refractive index by photolocking of the radicals produced by photodecomposition of BDK. 12,13 Thus, BDK in the SGHG films can act as a refractive index modifier as well as a photoinitiator.…”