# 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
They first reported on octavinyl T\({}_{8}\) cage functionalization, performing a [Pd(P\({}^{\mathrm{t}}\)Bu\({}_{3}\))\({}_{2}\)]-mediated reaction with bromopyrene [46]. This was performed to obtain complete substitution (8-substituted as most abundant-P8) in comparison to the double Heck reaction product (14-substituted as most abundant-P14) with a \(>\)80% yield that was thermally stable up to 495 \({}^{\circ}\)C. These two systems were also analyzed in terms of their photoluminescence properties in solution (toluene), \(\lambda_{\mathrm{em}}\) = 425 nm (P8) and 431 nm (P14), as well as in thin films, \(\lambda_{\mathrm{em}}\) = 494 nm (P8) and 506 nm (P14). This meant a 70-75 nm red-shift effect when compared results in solution vs. in a solid state that suggested possible pyrene unit aggregation. The problem of two high \"density\" pyrene units was resolved by performing an efficient functionalization of vinyl-substituted T\({}_{8}\), T\({}_{10}\) and T\({}_{12}\) cages with bromopyrene and a mixture of bromopyrene and a smaller steric reagent (i.e., 4-heptylbenzene) using the same catalytic Pd system (Figure 7) [47]. Obtained products (i.e., monopyrene(heptaisobutyl)silesquioxane, along with the pyrene/heptylstyrene- substituted T\({}_{8}\), T\({}_{10}\) and T\({}_{12}\) cage product mixture) were analyzed with TGA (ThermoGravimetric Analysis), showing their high thermal stability up to 359-469 \({}^{\circ}\)C. The films prepared (using solution-processed deposition) from the obtained materials exhibited a sky-blue emission (\(\lambda_{\mathrm{em}}\) in the range of 459-486 nm for thin films, and \(\lambda_{\mathrm{em}}\) in the range of 400-449 nm for the toluene solution). These results may also suggest chromophore aggregation in a solid state. The obtained compounds were tested in solution-processed OLEDs prepared to obtain materials showing current efficiencies of 3.64% and 9.56 cd A\({}^{-1}\), respectively. [PERSON] et al. presented a Heck coupling-based strategy to obtain anthracene-substituted T\({}_{8}\) cage via a [Pd(OAc)\({}_{2}\)]/PPh\({}_{3}\)-catalyzed reaction at room temperature in various reagent stoichiometry resulting in differently substituted products (Figure 8) [48]. The substitution was also statistical, but with the majority of the presented forms of products that depended on the possibility to form a complex between palladium with bromoanthracene substrate. Their \(T_{4}\)\({}^{5\%}\) in the range of 407 \({}^{\circ}\)C (H3), 468 \({}^{\circ}\)C (H1) and 480 \({}^{\circ}\)C (H2), respectively, suggest high thermal stability in comparison with bromoantracene \(T_{\mathrm{d}}\) = 246 \({}^{\circ}\)C. The photophysics were verified  
Figure 8: Heck coupling of OVS leading to mono-, di- and tri- anthracene-functional POSS. and the UV-vis spectra revealed the presence of three absorption maxima wavelengths \(\lambda_{\mathrm{ab}}\) = 356, 373 and 390 nm for solution in toluene. The emission spectra were recorded in toluene, showing emission maxima wavelengths \(\lambda_{\mathrm{em}}\) = 440 (H1), 461 (H3) and 458 (H2) nm, which were compared to the spectra for solids that disclosed red-shifts \(\Delta\lambda\) = 42-51 nm, suggesting known phenomena of possible anthracene unit aggregation (the smallest effect for H1). The same authors reported on the further modification of dianthracene(hexavinyl)octasilesquisoxane (H2), and using Heck coupling to introduce one diazophenylnablenediamine moiety followed by an amidation process to introduce a complex structure of a chromophore that possess broad-band absorbing properties [49]. The presence of different chromophores allows the absorbing bands of the dyes to be combined, reduces the possibility of their aggregation and possesses a broad red-emission band at \(\lambda_{\mathrm{em}}\) = 638 nm. Completely octa-substituted T\({}_{8}\) cage obtained via Heck coupling reaction was reported by [PERSON] et al.