# Synthetic Routes to Silsesquioxane-Based Systems as Photoactive Materials and Their Precursors
## 1 Introduction
### Cross-Metathesis and Related Modifications for Silyalkenyl Fragment Formations
Many of these criteria are subjective and depend on a certain type of a process, but several reactions fit the concept better than others, and have been applied in the chemistry of silsesquioxanes [118]:  
* [3+2] cycloadditions, such as Huisgen 1,3-dipolar cycloaddition and particularly Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC)
* thiol-ene coupling reaction (TEC)
* strain-promoted azide-alkyne cycloaddition (SPAAC)
* Diels-Alder reaction
* thiol-Michael addition
* oxime ligation  
One of these processes, applied in the synthesis of silsesquioxanes, is the 1,3-dipolar Huisgen cycloaddition of azides to alkynes, to give form 1,2,3-triazole (CuAAC) [119]. This is a catalytic reaction, mediated mostly by copper(I) salts (but also ruthenium or silver) and reducing agents (e.g., sodium ascorbate) [118,120]. A combination of the 1,3-dipolar Huisgen process followed by palladium Sonogashira coupling was used in the synthesis of oligophenyl-ethynylenes with heptaisobutylsilsesquioxane used as pendant groups by [PERSON] et al. (Figure 36) [121]. These two consecutive processes turned out to be efficient methods (84-99% yields) for the synthesis of interesting, highly \(\pi\)-conjugated organic systems, with silsesquioxane units at two independent molecule fragment, of high thermal stability (\(T_{\mathrm{d}}\)\({}^{5\%}\) up to 369 \({}^{\circ}\)C and exhibited \(T_{\mathrm{g}}\) in a range of 80-197 \({}^{\circ}\)C for R\({}^{\prime}\) = Phe oligo-pPE POSS). Their photophysical properties were analyzed in solution (THF) and also in a solid state. While the maxima absorption in solution equaled \(\lambda_{\mathrm{ab}}\) = 373-403 nm, the emission spectra (excitation at 350 nm) shift from deep blue to sky blue, and red-shifted (\(\lambda_{\mathrm{em}}\) = 409-443 nm) as the amount of aromatic fragments of end-capping molecules increased, as well as with the extended conjugation of in the main chain. The emission spectra of photoluminescence measured in the solid state were strongly shifted towards longer wavelengths (\(\lambda_{\mathrm{em}}\) = 470-533), which resulted in interchain orbital interactions referred to aggregation bands. Nevertheless, the extended \(\pi\)-conjugation of oligo-pPEs POSS maintained relatively high photoluminescence quantum efficiencies when compared to mono-pPEs POSS. The authors reported on the preliminary and successful use of mono- and oligo-pPEs POSS (R\({}^{\prime}\) = Py) as active dopants in the fabrication of dye-doped OLED devices. An interesting example of octazido-functional POSS was reported by [PERSON] et al. with two types of functionalities of different stoichiometry obtained via a 1,3-dipolar Huisgen reaction (Figure 37) [122]. The authors used octa(azidomethylene)spheresosilicate obtained as an efficient azido-bearing reagent [123]. The synthetic procedure was based on a different kind of copper complex, along with the reducing agent (i.e., [Cu(PPh\({}_{3}\))\({}_{3}\)Br] and KF) that resulted in very high yields of products  
Figure 17:2 Synthesis of oligophenyl-ethynylenes with heptaisobutylsilsesquioxane as pendant groups via a 1,3-dipolar Huisgen reaction followed by palladium Sonogashira coupling. bearing two types of functionalities B and Y: W\({}_{71}\), W\({}_{62}\) and W\({}_{53}\), which abbreviations derive from the stoichiometry of the acetylenes applied. The obtained compounds were thermally more stable (\(T_{\rm g}\) in a range of 192-273 \({}^{\circ}\)C) than their organic counterparts (B and Y). Their photophysical properties were analyzed in comparison to the acetylenes (B and Y) as reference molecules in solution and in a solid state. The absorption and emission spectra (shape, intensity and also \(\lambda_{\rm em}\)) of the acetylenes were dependent on the solvent use, and were collected in THF and also THF/water (from a 0 to 90% water fraction). Additionally, the emission spectra of Y were strongly fixed on the amount of water content and were red-shifted ca. 60 nm.