# Synthetic Routes to Silsesquioxane-Based Systems as Photoactive Materials and Their Precursors
## 1 Introduction
### Cross-Metathesis and Related Modifications for Silyalkenyl Fragment Formations  
Cross-Metathesis (CM) is one of the fundamental catalytic transformations in the chemistry of organosilicon compounds [67]. In this manner, it is a TM-carbene-mediated (TM = Ru, Mo, etc.) process of C=C bond cleavage and formation of unsaturated organosilicon derivatives. Silsesquioxane, which are promising precursors with Si-HC=CH\({}_{2}\) reactive moiety may be placed in this group of reagents [68; 69; 70; 71]. CM may be applied as a single synthetic route leading to desired POSS-based compounds, or used as a valuable tool for obtaining precursors of silsesquioxanes with reactive groups for consecutive reactions (e.g., Heck or Sonogashira coupling). In this matter, the described process was used to obtain a series of compounds exhibiting interesting photophysical properties. [PERSON] et al. contributed to this issue with the use of octavinyl silsesquioxane (OVS) grafted with styrene derivatives using [PERSON] first generation catalyst (4 mol %) and 2-3 equiv. of styrene per one Si-HC=CH\({}_{2}\) group and resulting in good 67%-78% product yields (Figure 16) [72; 73]. The modifications of styryl rings resulted in changes in absorption and emission spectra, especially when aldehyde moiety was introduced and resulted in quenching emission. The POSS derivatives were reported to exhibit red shifts and broader spectral emissions due to the involvement of a silsesquioxane core in electronic delocalisation. It should be noted that CM reaction conditions may be improved so that not as much styrene excess is required to complete OVS conversion (24 h) [74]. Figure 16: Cross-metathetic reaction path for the synthesis of octa(styryl)silsesquioxane. Figure 15: Synthesis route for octa-substituted T\({}_{8}\) phenylacetylenes obtained via Sonogashira reaction. Cross-metathesis was employed as precursor synthetic process for obtaining mono(p-bromostyryl)heptaisobutylsilsesquioxane (M1-Br) by [PERSON] et al. [75]. This compound was applied as a reagent in two subsequent Sonogashira coupling reactions, resulting in dumbbell-shaped \(\pi\)-conjugated systems with POSS as pendant groups (Figure 17). Unfortunately, the reaction conditions were based on the use of 3 equiv. of para-bromo-styrene, and 3 mol % of Grubbs first generation catalyst (added to the reaction in two portions) enabled the formation of precursor M1-Br with only a 68% yield, contrary to the procedure developed in our group [76]. The next steps of the process were performed with moderate 37%-58% yields of respective final dumbbell products (DA13). These were characterized in terms of their photophysical and thermal properties in comparison with their organic counterparts. Their \(T_{\mathrm{d}}\)1\({}^{\mathrm{\%}}\) was respectively high (268-282 \({}^{\circ}\)C). The interesting part of the research concerns absorption and emission spectra performed in a solution vs. in a solid. The \(\lambda_{\mathrm{em}}\) maxima in the solid state were red-sifted in a range of 34-50 nm and equaled 401, 542 and 520 nm for DA13, respectively. This was noticed after UV irradiation (352 nm) that revealed blue, yellow and greenish-yellow emissions in POSS-based systems contrary to their organic analogues. These results also indicate the participation of the Si-O-Si cage in the delocalization of electrons, and prevention of the \(\pi\)-conjugated parts from interaction. [PERSON] et al. have profoundly contributed to the development of cross-metathetic transformation using the most useful reagent in this process (i.e., octa(vinyl)silsesquioxane T\({}_{8}\) (OVS), but also decavinylT\({}_{10}\) and dodecavinylT\({}_{12}\) cages). The selective introduction of substituted (E)-styrenyl moiety at Si-O-Si cores and for the promo-derivatives enabled their consecutive modification via Heck coupling (Figure 18) [71; 77].