# Synthetic Routes to Silsesquioxane-Based Systems as Photoactive Materials and Their Precursors
## 1 Introduction
### Heck Coupling for Obtaining Silylakenyl Units Anchored at the Si-O-Si Core
and used for the synthesis of a water-soluble hybrid nanodot based on POSS and conjugated electrolytes for the Two-Photon Excited Fluorescence (TPEF) analysis that imaginesthe cellular and cancer nuclei (Figure 9) [50,51]. The Two-Photon Excited Fluorescence is a microscopic method used to reduce photodamage to a cell, improve resolution and minimize cellular autofluorescence, but it has rarely been exploited, due to the lack of efficient absorption materials that can enter nuclei and in turn selectively stain them. The desired fluorophore was anchored to the POSS core via a Heck coupling procedure of octavinyl silsesquioxane (OVS) and respective monobromo-substituted chromophore in the presence of [Pd(OAc)\({}_{2}\)/P(o-Tol)\({}_{3}\)] with a 45% yield. The quaternized silsesquioxane derivative was soluble in water and its average diameter of 3.6 \(\pm\) 0.3 nm enabled easy penetration of cellular nuclei. The photophysical properties were verified and absorption maxima \(\lambda_{\mathrm{ab}}\) bands at 320 and 465 nm corresponded to the fluorene and benzothiazole units, but they red-shifted by 34 and 75 nm, respectively, due to the -HC=CH-POSS moiety extending the conjugation system. On the other hand, the \(\lambda_{\mathrm{em}}\) was located at 617 nm and exhibited a large Stokes effect at 152 nm. An interesting scientific concept was proposed and performed by [PERSON] et al., who used octavinyl silsesquioxane (OVS) and multibromo-substituted arenes in a Heck Coupling process to yield crosslinked 3D networks of highly hyperbranched structures with a \(>\)80% yield (Figure 10) [52,53]. The reaction procedure was also modified by using mixtures of different chromophores (e.g., BP and Py) in various stoichiometry, which resulted in the formation of macromolecular 3D systems with different chromophore content. The purification procedures of obtained polymeric materials, due to  
Figure 10: Synthetic route leading to hyperbranched 3D POSS-based materials obtained via Heck coupling. Figure 9: Efficient Heck coupling for the formation of octa-substituted T\({}_{8}\) with conjugated fluorene and benzothiazole units. their 3D structure, was necessary due to the presence of non-reacted comonomers, and post-reaction inorganic salts and other residues within the matrix. The isolation was mostly based on filtration and washing with different solvents. For this reason, a Soxhlet apparatus was used with THF and MeOH to obtain pure products. All of the obtained compounds were analyzed in terms of their proven thermal resistance and high \(T_{\mathrm{d}}\)\({}^{5\%}\) at -390 \({}^{\circ}\)C, but the high porosity of these materials was revealed by during BET (Brunauer-Emmett-Teller) analysis. Depending on the type (and amount, if mixture) of respective arene, respective hyperbranched products exhibited various surface areas from 358 to even 848 m\({}^{2}\)g\({}^{-1}\) (when M3 was used as a reagent). The most interesting part of the research was disclosed in defining the photophysical properties of both substrates (M1-M3, BP, Py). In the case of M1, M2 and M3, which showed high blue fluorescence (\(\lambda_{\mathrm{em}}\) at ca. 435 nm) in solid state and in solution (DCM = dichloromethane), the respectively obtained hyperbranched products showed strong red shifts (observed at \(\lambda_{\mathrm{ex}}\) = 365 nm), and green (\(\lambda_{\mathrm{em}}\) = 509 nm for prod.1, derived from M1; \(\lambda_{\mathrm{em}}\) = 518 nm for prod.2, derived from M2) or yellow (\(\lambda_{\mathrm{em}}\) = 540 nm for prod.3, derived from M3) fluorescence. This may be derived due to the extended \(\pi\)-\(\pi\) conjugation in the 3D network by additional -HC=CH- linkage. The ethanol dispersion of these materials was applied to obtain sensors for various nitroaromatic explosives by fluorescence quenching [53]. On the other hand, modulation of the stoichiometry of BP and Py in Heck coupling with OVS resulted in the formation of nine types of materials that altered the amount of BP and Py units in the frameworks.