## 1 Introduction  
Synthesis of heteroatomic \(\pi\)-conjugated systems for opto-electronic applications is a highly developed research field since two decades [1]. Following the successful incorporation of thiophene oligomers and polymers in opto-electronic devices, [1; 2; 3] new derivatives featuring B [4; 5], N [6; 7], O [8; 9], Si [10] or P [11; 12; 13; 14; 15; 16; 17; 18; 19] have been developed. In particular, siloles (silacyclopentadienes) found promising applications in the field of organic light emitting devices (OLEDs) [20; 21; 22; 23]. Two main reasons explain the good behaviour of siloles in these devices. First of all, the \(\pi^{\ast}\)-\(\pi^{\ast}\) hyperconjugation between the exocyclic Si-C bonds and the \(\pi^{\ast}\) orbital of the butadiene moiety drastically lower the LUMO of the siloles, thus enhancing its electron transport ability [10]. Furthermore, the presence of phenyl (or (hetero)-aryl) substituents in the 2,3,4,5 positions of the silole ring (derivative **A**, Figure 1) make it a very efficient solid-state emitter due to the so-called Aggregation-Induced Emission (AIE) effect [24; 25; 26; 27]. This particular effect is attributed to the restriction of intramolecular rotation of the lateral phenyl rings in the aggregated state. The combination of good charge transport properties as well as high photoluminescence quantum yields in the solid state explain the good performances of the devices. Furthermore, following the pioneering work of [PERSON], [PERSON] et al., new synthetic pathways have been developed to prepare silole-containing polyacenes **B** (Figure 1), namely Si-containing ladder-\(\pi\)-conjugated systems [28; 29; 30; 31; 32; 33; 34; 35; 36]. Others families of fused silole derivatives such as Si-containing helicenes [37; 38] and small 2D Polycyclic Aromatic Hydrocarbons (PAHs) [39] were also recently prepared. Other than the synthetic challenge of preparing these derivatives, they appeared highly emissive in solution. However, poor solid-state emission was reported due to strong packing and thus no electroluminescent devices based on these structures have been prepared. However, planar molecules can be used as emitters in OLEDs if an efficient control of the packing of these planar structures in solid state is achieved, allowing to restore their emissive properties. For example, we recently reported on the preparation of ladder-benzofuran fused phospholes **C** (Figure 1) showing efficient electroluminescent properties in OLEDs if the compound **C** is diluted in a 4,4'-bis(2,2-diphenylvinyl)-1,1'-biphenyl (DPVBi) matrix [40]. Since Si-containing planar-\(\pi\)-conjugated systems (Figure 1B) and benzofuran fused-\(\pi\)-conjugated systems (Figure 1C) are highly efficient emitters, we decided to develop and study the properties of Si,O-ladder \(\pi\)-conjugated systems (Scheme 1) as potential efficient fluorescent emitters in OLEDs.  
In the present article, we report on the use of blue-emitting Si,O-ladder \(\pi\)-conjugated systems as emitters in OLEDs showing that these systems can find applications in electroluminescent devices. Furthermore, we detail their synthesis and electronic properties determined experimentally (UV-vis, fluorescence, electrochemistry) and theoretically (density functional theory (DFT)).