# 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
As a result, they exhibited continuous color change from bluish-green at \(\lambda_{\mathrm{em}}\) = 485 nm, to green at \(\lambda_{\mathrm{em}}\) = 528 nm, yellow at \(\lambda_{\mathrm{em}}\) = 555 nm and finally to red at \(\lambda_{\mathrm{em}}\) = 605 nm. High fluorescence quantum yields in the solid state were calculated and ranged from 2.46% to 22.42% [52]. These systems were used along with the thiol-containing polysiloxane matrix to produce a UV-LED device that shows color-transformable properties by simply turning the irradiation on and off. Heck coupling using the silsesquioxanes may be performed also in the reverse functional group placement (i.e., to applied octa(halogenophenyl)silsesquioxane and styrene derivatives as a source of -HC=CH\({}_{2}\) moiety). Respective research on this issue was pioneered by [PERSON] et al. [54]. The primary reagent for the study was cubic octa(phenyl)silsesquioxane (OPS) that was subjected to bromination via a Fe-catalyzed reaction that resulted in [octa(polybromophenyl)]silsesquioxane. The resultant compounds had a different substitution of bromine at the Ph ring, but this could be controlled by reaction stoichiometry to obtain a para-brominated 2,5-dibrominated derivatives. A more-efficient and selective procedure for the synthesis of analogously octa(p-iodophenyl)silsesquioxanes using ICI was also reported [55; 56]. These two systems are perfect halogenophenylIPOSS reagents for the Heck and other coupling processes (e.g., Suzuki-type) [57]. In 2010, [PERSON] et al. reported on synthesis of a series of octa(stillene)silsesquioxane derivatives using octa(p-iodophenyl)silsesquioxane and octa(bromophenyl)silsesquioxanes (on average 67% p-substituted, 24% meta, 9% ortho and 3% disubstituted) with respective p-substituted sytrenes in Heck coupling reaction conditions (i.e., [Pd\({}_{2}\)(dba)\({}_{3}\)] (1 mol %)/[Pd(P\({}^{\mathrm{\prime}}\)Bu\({}_{3}\))\({}_{2}\)] (2 mol %) that resulted in octa(stillene)silsesquioxanes with diverse p-phenyl substituents with high 62-86% yields (Figure 11) [58]. Figure 11: Heck coupling using halogenophenylIPOSS reagents. The desired octa-substituted products were also accompanied by compounds with not-completely substituted phenyl rings, which was a result of not-fully halogenated octa(phenyl)silsesquioxane, especially in the case of Br [54]. The corresponding products were characterized in terms of their thermal resistance (\(T_{\mathrm{d}}\)5\({}^{\mathrm{\%}}\) in the range of 318-429 \({}^{\mathrm{\circ}}\)C). The greatest emphasis was placed on their photophysics assessment and its comparison with trans-stilbene and Me-stilbene-Si(OEt)\({}_{3}\). The UV-vis spectra of products (in THF) were similar in shape and red-shifted 5-10 nm (\(\lambda_{\mathrm{ab}}\) 298-320 nm) to their molecular counterparts, but their large red shift of 60-100 nm was visible for the emission spectra of these systems when compared with trans-stilbene and Me-stilbene-Si(OEt)\({}_{3}\) (\(\lambda_{\mathrm{em}}\) 334-436 nm). The greatest difference was noted for stilbene and p-Me-stilbene silsesquioxane derivatives that were also collated with UV-vis and PL spectra for octa(p-Me-stilbene)silsesquioxane and its hepta(p-Me-stilbene)phenylsilsesquioxane. Altogether, the absorption-emission changes that were observed along with the theoretical calculations and additional analysis of stilbene-siloxane and cyclosiloxane, respectively, suggest that the large red-shift may have resulted from interactions of the stilbene \(\pi^{\circ}\) orbitals with a LUMO located inside the cage and involving all Si and O atoms, as well as the organic substituents that interact in the excited state. Interestingly, for the NMe\({}_{2}\) derivative the solvatochromism phenomenon was observed mainly due to the charge-transfer interaction when the polarity of solvent was changed. Studies on stilbene derivatives of silsesquioxanes were also conducted.