# Synthetic Routes to Silsesquioxane-Based Systems as Photoactive Materials and Their Precursors
## 1 Introduction
### Heck Coupling for Obtaining Silylakenyl Units Anchored at the Si-O-Si Core
One of the aspects to be studied was the usage of octa(halogenephenyl)silsesquioxane reagents substituted with bromine at phenyl ring in different places (i.e., octa(o-bromophenyl)silsesquioxane, but also octa(2,5-dibromophenyl)silsesquioxane and octa(2,4,5-dibromophenyl)silsesquioxane) [59]. This provided more functionalities per unit volume, exceeding the density when compared to POSS-based dendrimers. These compounds were used for analogous Heck coupling procedure (including catalytic systems, etc. ), leading to corresponding octaphenyl silsesquioxane (OPS)-based syrenes with 8, 16 and 24 styryl substituents, with R = 4-Me, R = 4-NBoc and R = 4-Ac groups, respectively [60]. Interestingly, the thermal parameter for these systems is similar to their octa-substituted derivatives. The blue shift of the absorption and the red shift of the emission spectra for the (R-o-styryl)\({}_{8}\)OPS suggest the interactions of the Si-O-Si cage with the ortho-substituted organic groups. On the other hand, the (Rstyryl)\({}_{16}\)OPS exhibited a longer conjugation length, resulting in higher values of Stoke's shift and (Rstyryl)\({}_{24}\)OPS behavior that revealed the existence of both a regular \(\pi\)-\(\pi^{\bullet}\) transition and a charge transfer, which could be explained by two excited states involving the LUMO inside the Si-O-Si cage. The synthetic procedure of Heck coupling was also conducted in a controlled copolymerization of octa(p-iodophenyl)silesesquioxane with 1,4-divinylbenzene (DVB) and 1,4-diethylbenzylbenzene (DEB). [PERSON] et al. reported on a specific formation of copolymeric systems derived from octa(p-iodophenyl)silesesquioxane embedded between DVB or DEB fragments (Figure 12) [61]. Figure 12: Synthetic approach for linear copolymers obtained via consecutive Heck and Sonogashira coupling. The synthetic routes that were tested were based on changing the reaction sequence of octa(p-iodophenyl)silsesequioxane Heck Coupling functionalization (carried out with specific stoichiometry) and linking each silsesquioxane via Heck or Sonogashira cross-coupling with DVB or DEB. The procedure resulted in final copolymeric systems with a moderate 39%-51% yield and respected average molecular weights in the range of 9-30 kDa, as well as suggesting that the formation of di(p-iodostyryl)hexastyrylsilsesquioxanes as the first reaction sequence results in higher molecular weights of the resulting copolymeric systems. The photophysics of the two types of copolymers significantly depended on the organic linker. The DVB copolymers exhibited very little conjugation due to high 1,4-DVB fragments, whereas the DEB showed a strong red-shift at ~40 nm emission. This suggests electron delocalization through the Si-O-Si cage. Again, the p-aminostilbene copolymer derivative showed charge-transfer stabilization. [PERSON] and co-workers expanded the studies conducted on T\({}_{10}\) and T\({}_{12}\) cages with reactive Si-HC=CH, p-iodophenyl and bromophenyl substituents. They previously reported on the possibility of fluoride ion (TBAF = tetra-n-butylammonium fluoride) catalyzed cage rearrangements between polyvinyl- and polyphenylsilsesquioxane, resulting T\({}_{10}\) and T\({}_{12}\) with mixed reactive group placement (depending on the reaction condition and stoichiometry) [30; 31]. The research concerned using vinylT\({}_{10/12}\) cage mixture and its functionalization using Heck and double Heck coupling with bromostyrene, 1-bromonaphthalene and 9-bromoanthracene, as well as Grubbs first generation catalyzed cross-metathesis of the vinylT\({}_{10/12}\) with p-substituted syrenes (Figure 13) [62]. In parallel, the reverse Heck Coupling (i.e., reaction) of (Br-styrenyl)T\({}_{10/12}\) cage mixture with p-substituted syrenes was conducted (Figure 14). The results for both processes are presented here for the ease of their comparison (CM is described in Section 3.3). The described catalytic processes are parallel routes for analogical T\({}_{10}\) and T\({}_{12}\) structure formations, and also similarly efficient.