# Synthetic Routes to Silsesquioxane-Based Systems as Photoactive Materials and Their Precursors
## 1 Introduction
### Cross-Metathesis and Related Modifications for Silyalkenyl Fragment Formations
These results suggest that the PL of **1** clearly demonstrates the aggregation-enhanced emission (AEE) of this molecule. Similar emissive behavior was also observed for **2**. For a quantitative comparison, measurements of fluorescence quantum were performed. The absolute fluorescence quantum values of the thin solid films of both products reached as high as 51% and 45%, respectively, meaning they were higher than those of their corresponding parent silole molecules in the solid state. Obtained results proved that the POSS core improved the fluorescence quantum yield of the AEE materials in both the solution and in the aggregated state. Figure 15:6 Hydrosilylation-based functionalization of Q8M8 and Q8V8 with allyl-tetraphenylsilole and hydrosilylphenyl-tetraphenylsilole. Further examples of the use of silsesquioxane derivatives in hydrosilylation with azo-chromophores in order to form functionalizable POSS nanoparticles have been reported by the [PERSON], [PERSON] and [PERSON] groups independently [105; 106; 107; 108; 109]. The procedures, allowing the synthesis of POSS derivatives with azobenzene mesogenes, have been proposed via the hydrosilylation of respective octahydro-substituted T\({}_{8}\) silsesquioxanes. Selected structures of final materials **(1-10)** are presented in Figure 15:7  
[PERSON] presented a group of azobenzene-containing POSS-based star-like hybrid functional materials obtained via hydrosilylation octahydroidosilesquioxane with three different azobenzene chromophores containing terminal alkynyl moiety as the reactive fragments [109]. The reactions were carried out in the presence of platinum dicyclopentadiene complex [Pt(dcp)] at 80 \({}^{\circ}\)C, using an eight-fold molar excess of olefin relative to silsesquioxane. However, the process was not selective, and expected products were obtained as a mixture of \(\alpha\)- and \(\beta\)-adducts with yields ranging from 48% to 54%. Analyzed thermal stability was proved to be higher than of the respective chromophores and suggests its enhancement with anchoring chromophores onto POSS core. Interestingly, the authors did not observe any sign of melting or glass transition of the products up to the decomposition temperatures, though all substrates were crystalline solids. These amorphous characters of compounds may result from a star-like structure with rigid azobenzene chromophore units protruding from a spherical POSS core in 3D thus minimizing any \(\pi\)-\(\pi\) interactions. The photophysical properties of all products were disclosed using UV-vis and PL analyses, and were compared with their organic analogues. Product 10 and its corresponding azobenzene chromophore displayed nearly the same maximum absorption wavelengths and spectral pattern, indicating that Si-O-Si core has no significant effect on the electronic structure of the final material. The UV-vis spectra of products (8-10) in THF showed strong absorption bands at \(\lambda_{\text{ab}}=\) 356, 347 and 365 nm, respectively, which can be assigned to the \(\pi\)-\(\pi^{\star}\) local electron transition of the azobenzene fragments. It was also proven that azobenzene moieties influence the \(\lambda_{\text{ab}}\) (e.g., the maximum absorption peak of compound **9** shows a 9 nm blue shift compared to that of **8**, which may have resulted from the rigid spacer -PhCOO- unit twisting the planar azobenzene fragment. Analogous results were achieved for spectra recorded in a solid state (\(\lambda_{\text{ab}}=\) 360, 347 and 366 nm). This suggests the star-type structure in products enables avoiding the aggregation for azobenzene units in solid state. The authors showed that obtained materials had good film-forming properties, high thermal stability and novel optical limiting properties that could be potentially applied as opto- and electroluminescent materials. [PERSON] et al. reported on two types of novel nanoparticles based on a POSS surrounded by eight covalently attached units of azobenzene mesogens differing in the length of their aliphatic chains **(1, 2)** (Figure 32) [105; 106].