# Synthetic Routes to Silsesquioxane-Based Systems as Photoactive Materials and Their Precursors
## 1 Introduction
### Cross-Metathesis and Related Modifications for Silyalkenyl Fragment Formations
The reaction conditions, catalytic systems and reagents' structures influence the stereo-or even regioselectivity of hydrosilylation leading towards saturated and unsaturated molecular,  
Figure 21: Synthetic protocol for stereoselective silylative coupling and cross-metathesis with olefins/dienes of divinyl-substituted DDSQ systems. but also macromolecular organosilicon systems [82]. Hydroosilylation is also a very popular catalytic procedure to anchor organic dyes onto a Si-O-Si core of a cubic T\({}_{8}\) cage (POSS) or a double-decker (DDSQ) type. [PERSON] and [PERSON]'s group reported a new type of POSS derivative containing carbazole as a photo- and electroactive chromophore [89; 90]. The carbazole unit was introduced via hydrosilylation between octa(dimethylsiloxy)silesquisoxane (Q\({}_{8}\)M\({}_{8}\)) and 9-vinylcarbazole in the presence of commercially available [PERSON]'s ([Pt\({}_{2}\)(dvds)\({}_{3}\)]) as well as [PERSON]'s (H\({}_{2}\)PtCl\({}_{6}\)) catalyst (Figure 22). The reaction was performed in dry toluene using a small excess of olefin to ensure complete conversion of the reactants, and it led to the formation of the expected product with a 70% yield. Its TGA showed that the product was stable up to \(\sim\)400 \({}^{\circ}\)C in air, and 450 \({}^{\circ}\)C in N\({}_{2}\) (i.e., it exhibited higher stability than its organic analogoue, poly(9-vinylcarbazole) (PVCz), which was also proved by DSC anaysis and was expected by POSS addition). The \(T_{g}\) = 37 \({}^{\circ}\)C was much lower than that of the PVCz (\(T_{g}\) = 190 \({}^{\circ}\)C) due to the flexible spacer between POSS and carbazole. The photophysical parameters were analyzed in solution (THF) and in a solid state, and were compared to their organic couterparts (9-ethylcarbazole (EtCz) and poly(9-vinylcarbazole) (PVCz)). The emmision spectrum of the product (\(\lambda_{\mathrm{ex}}\) = 250 nm) showed two peaks, \(\lambda_{\mathrm{em}}\) = 353 and 370 nm, which is almost the same as that of the EtCz. Similar compatibility was obtained in terms of quantum yields in air (\(\Phi_{\mathrm{P}}\) = 0.27 and \(\Phi_{\mathrm{EtCz}}\) = 0.30). On the other hand, the PVCz showed weak and broad peaks with a lower quantum yield (\(\Phi_{\mathrm{PVCz}}\) = 0.10) resulting from the formation of excimer. The \(\lambda_{\mathrm{em}}\) for solids was more red-shifted towards the wavelength region 350-400 nm and 450 nm, indicating a greater aggregation in crystalline product than that in amorphous material, but the values of the photoluminescence quantum yields were the same. The result suggests that the introduction of the rigid POSS core isolated each of the carbazole units, preventing their aggregation and the formation of excimer, which resulted in a useful concept to apply this new material in a solid-state optoelectronic device. Interesting research on the synthesis of carbazole-substituted double-decker-shaped silsesquioxane (DDSQ-4 Cz) also obtained via a hydrosilylation reaction (mediated by [PERSON]'s catalyst) was presented by [PERSON] et al. (Figure 23) [91]. The obtained material's thermal stability was higher than 355 \({}^{\circ}\)C. Photophysical properties of DDSQ-4 Cz were disclosed via UV-vis and photoluminescence analysis and compared with its organic analogue (N-vinylcarbazole). The absorption spectrum (in CHCl\({}_{3}\)) revealed of two peaks (\(\lambda_{\mathrm{ab}}\) between 325-350 nm) atributted to the \(\pi\)-\(\pi^{\ast}\) absorption of carbazole, which closely resembled that of N-vinylcarbazole. Interestingly, the photoluminescence spectra of DDSQ-4 Cz and N-vinylcarbazole  
Figure 23: Reaction path towards tetra(carbazole)-substituted DDSQ (DDSQ-4 Cz). Figure 22: Hydroisylation reaction towards efficient synthesis of octakis [2-carbazol-9-yl]-ethyldimethylsiloxy]silesquisoxane. were practically the same (\(\lambda_{\rm em}\) = 350-300 nm), indicating that the four carbazole units were isolated by the rigid core, thereby preventing excimer formation.