# Synthetic Routes to Silsesquioxane-Based Systems as Photoactive Materials and Their Precursors
## 1 Introduction
### Cross-Metathesis and Related Modifications for Silyalkenyl Fragment Formations
The compounds were selectively obtained in \(\beta\) isomers using [PERSON]'s  
Figure 15:8 The POSS derivatives with azobenzene-based chromophores obtained by hydrosilylation. cataly and obtained with 68.5% and 71% yields, respectively. The UV-vis spectra (in CHCl\({}_{3}\)) of the stable forms of **1** and **2** exhibited features that were characteristic of parent azobenzene molecules in the wavelength range 250-550 nm, as well as a strong \(\pi\)-\(\pi\) * band at \(\lambda_{\text{ab}}\) ca. 338 nm (for **1**) and 335 nm (for **2**) and much weaker broad bands with maxima at \(\lambda_{\text{ab}}\) ca. 445 nm (for **1**) and 440 nm (for **2**), respectively. These results suggest that, in equilibrium and at room temperature, the azobenzene units are predominantly in their trans configuration. Different absorption spectra were recorded after homogeneously being irradiated by intense broad UV light (360 nm) for 2 min. The disappearance of a band at 335 nm and the increase of intensity of the 440 nm band was observed. This transformation is characteristic of the reversible trans-cis isomerization process in azobenzene units. In further studies, the authors proved that the addition of the POSS compound with mesogenic branches containing azo dye undergo photoisomerization enhanced by UV light. The [PERSON] group presented a similar type of nanoparticles, but have reported two different approaches to fabricating azo-functionalized POSS compounds via [PERSON]'s mediated hydrosilylation. These were carried out in 48 and 72 h, with high 83-94% yields (Figure 32) [107; 108]. Firstly, they obtained branched azo-POSS structures based on azo dyes possessing flexible spacers of different chemical natures and lengths between the POSS core and the azobenzene units (**3**-**5**). Secondly, they synthesized the final material by isolating the azobenzene moieties with a constant short spacer between the azo dyes and POSS core (**6**, **7**). The product **7** was obtained as mixture of \(\alpha\) and \(\beta\) isomer, and the distribution of these isomers at molecular level was statistical. The higher thermal stability of all systems was proved (for products **3** and **5** the melting point temperatures were detected). The photophysical properties of all products were determined and compared with azo dyes (in solution and solid state). The UV-vis spectra of prepared azobenzene-modified POSS compounds showed two characteristic bands: \(\lambda_{\text{ab}}\) at 334-347 nm, which was related to the \(\pi\)-\(\pi\)* transition of the trans-azobenzene form, and \(\lambda_{\text{ab}}\) at 427-443 nm, originating from a typical n-\(\pi\)* transition. It was also observed that \(\lambda_{\text{ab}}\) peak positions (\(\pi\)-\(\pi\)*) of the initial substrates were identical to their respective POSS products. However, the absorption bands corresponding to \(\pi\)-\(\pi\)* transition in the trans isomers of all products were broader. This may have resulted from partial chromophore-chromophore aggregation of the azobenzene moieties. The UV-vis absorption spectra of the prepared films closely resembled solution spectra. Moreover, the products with the isolated azobenzene fragments (**3**-**5**) revealed a significant decrease in the trans-cis photoisomerization rate in solution as compared to other systems (**6**, **7**). In the solid state, the photoisomerization rates of all products were almost the same. These results indicate that the presence of isolation groups effectively prevents aggregation of substituents attached to the POSS core in films. A different part of POSS-based frameworks exhibiting interesting photophysical properties are TM complexes, mainly Ir and Pt, that are anchored by functional groups playing the role of a ligand to the silsesquioxane core. The phosphorescent TM complexes used as emitters in OLEDs have attracted much attention because they can utilize singlet as well as triplet excitons through spin-orbital coupling with metal ions [110].