# Synthetic Routes to Silsesquioxane-Based Systems as Photoactive Materials and Their Precursors
## 4 Conclusions  
The continuous demand for novel hybrid materials of specific applications inspires researchers to develop new synthetic procedures in modular and efficient ways. In this review, we have concentrated on the last decade, most effective routes for synthesizing functionalized polysilesquisoxanes to be employed in POSS-based photoactive materials and/or their precursors.  
* The first and essential step towards the synthesis of the abovementioned frameworks is the stoichiometric, hydrolytic condensation of prefunctionalized chloro- or alkoxysilanes, to constitute a basic silsesquioxane core with respective reactivity. These systems are, in turn, the basis for further modification (i.e., the introduction of highly functionalized organic moieties of complex architecture, usually and profoundly via catalytic methods).
* Heck coupling (HC) reactions catalyzed by palladium complex proceeding between C=C bond (especially SiCH=CH\({}_{2}\)) and aryl halides is a reaction very commonly applied for the synthesis of \(\pi\)-conjugated arene systems and related optoelectronic compounds. The respective Sonogashira coupling (i.e., a reaction of aryl halides with terminal alkynes) is much less frequently used.
* Olefin cross-metathesis (CM), as well as silylative coupling (SC) reactions, enable the formation of silylalkenyl moieties, which may be obtained in the presence of Grubbs ruthenium carbene (Ru = CHPh) (CM) or Ru-H/Si (SC) catalyst. These are the other generally effective and highly selective methods. Also, Ge-HC=CH\({}_{2}\) group in germasillesquioxane undergo effective cross-metathetic transformation.
* Hydroisylation of olefins and/or acetylenes is performed predominantly with hydrospherosilicate and catalyzed by TM (usually Pt) complex, and is prevalent reaction that can be efficient step towards the synthesis of optoelectronic materials. Additionally, when dihydro-substituted silsesquioxane (especially DDSQ) is applied as a reagent, the formation of respective macromolecular (polymeric) material with a Si-O-Si core embedded can be also obtained.
* In the last part of this review, other catalytic processes leading to the functionalized silsesquioxane of potent optoelectronic materials was collected.  
The methodology presented for the synthesis of POSS-based photoactive materials involves mono-, octa-functional cubic or double-decker silsesquioxanes. As was illustrated, the crucial aspect is to design a certain organic dye of respective photophysical properties (color of emitted light) and to anchor it on to the POSS core using the proper reaction procedure, which is dependent on the type of functional group at the Si-O-Si core. According to the perspective presented by experts in the chemistry of POSS-based photoactive compounds, this is now the next step required for the development of attractive and selective routes leading to multi-functional silsesquioxane derivatives with a markedly broadened application.  
B.D. and P.Z.--contributed equally to Conceptualization, Supervision, Writing original draft and Writing-review & editing; B.M.--Conceptualization.  
This research was funded by the National Centre for Research and Development of Poland [project No. PBS3/A1/16/2015] and the National Science Centre of Poland [project OPUS DEC-2016/23/B/ST5/00201].  
The authors declare no conflict of interest.