# Synthetic Routes to Silsesquioxane-Based Systems as Photoactive Materials and Their Precursors
## 1 Introduction
### Cross-Metathesis and Related Modifications for Silyalkenyl Fragment Formations
Platinum, and particularly iridium, are the most applicable metals, as they possess high quantum efficiency, brightness, a variety of colors and short excited-state lifetimes, and may be used as an alternative to classical OLEDs or in electrochemical devices, etc. On the other hand, silsesquioxane-based systems using conjugated arenes as substituents exhibit interesting photophysical and also thermal properties. Their incorporation into organic-light-emitting materials prevents aggregation of the organic moieties that lead to emission quenching and/or the lowering of quantum efficiency. The POSS core is suggested to act as a hybrid hole-transport material when compared to traditional hole-transport materials. Additionally, rigid Si-O-Si core improves the thermal stability of the resulting material. These silsesquioxane features have encouraged researchers to consider its application as a scaffold for organic substituents that play role of a ligand to anchor the metal ion and constitute a POSS-based complex. In this part, the proper choice of a coordination sphere for a desired complex (i.e., the presence of respective functional groups at the Si-O-Si core acting as donating groups in ligands, as well as modulating metal ancillary ligands), has evolved over the recent years, and interesting reports on TM complexes anchored onto silsesquioxane cores appeared. Their application in the fabrication of light-emitting devices has been observed previously [110]. The literature review suggests a hydrosilylation reaction (mediated by [PERSON]'s complex) as an easy methodology, since the bridge or spacer between the POSS core and the potential ligand play a minor role [111]. This is why the aliphatic connection resulting from hydrosilylation of alkene moiety by Si-H groups the predominant synthetic procedure that enables formation of POSS-based compounds and their use as potential ligands for TM-complex synthesis. [PERSON] et al. pioneered this issue and in 2009 reported on the efficient formation of a series of not only iridium-based, but also platinum-based complexes (Figure 33) [112; 113]. The synthetic procedure involved a few stages, which is a general approach for this kind of research. First, the proper design of an organic ligand structure is required. Usually the \(N\)- and \(O\)-based ligands are the most favorable, (e.g., based on acetylacetone and pyridine derivatives (2-phenylpyridine, 3-phenylisoquinoline), etc.). Formation of a respective alkenyl-functionalized linker, placed on the ligand moiety, was used for combining this molecule with the POSS core. Next, the selection and introduction of a proper ancillary ligand to the TM coordination sphere is important. The final part of the research concerns performance of a hydrosilylation reaction to anchor the complex with its functionality onto the POSS core. In these examples, the mono- and octa-substituted POSS was used as a reagent, with the -OMe2 Si-H moiety as reactive group. In the case of octa-functional systems, one Ir-based complex fragment and one and two Pt-based complex fragments were attached to the silsesquioxane. The rest of the Si-H moieties were reacted with allyl-carbazole. The authors obtained these systems with diverse yields, from very high (92%), to moderate (54-63%) and rather low (-20%), and their photophysical properties were analyzed (CHCl3, solid film). In general, the absorption properties of these molecules derive from the absorption of metal-to-ligand charge transfers (MLCT) at \(\lambda_{\mathrm{ab}}\) ca. 340-350 nm. The carbazole moieties, together with ligand-centered absorption units, result in shorter wavelengths. New emission peaks at \(\lambda_{\mathrm{em}}=465\) and 610 nm (green and green-yellow) from the complex with POSS system were red-shifted, especially in solid state for a molecule with two complex moieties in a molecule due to the excimer/aggregate states. Nevertheless, these systems were used in the fabrication of electroluminescent devices that revealed quantum efficiency to be enhanced. [PERSON] et al.