## 3 Results and Discussion
The solid-state luminescence of compounds **2**, **4-6** have been recorded in thin films. The solid-state luminescence of **2** is broadened and red-shifted as an effect of intermolecular interactions (see Figure S2). However, when bulky substituents are attached to the Si-atom (**4-6**), there is a good match between solution and solid-state luminescence (Figure S2), as the exocyclic fragments prevent intermolecular interaction. This is in good agreement with data previously reported for **4**[43]. The redox properties of compounds **2**, **4-6** has been investigated by cyclic voltammetry (CH\({}_{2}\)Cl\({}_{2}\) or THF, 0.2 M, TBAPF\({}_{6}\), v = 0.1 Vs\({}^{-1}\), see Table 1). All compounds show a reversible oxidation wave at relatively low potential and an irreversible reduction process at high potential. Compounds **4-6** display a mono-electronic oxidation wave at around +0.79 V (vs. Fc\({}^{+}\)/Fc) while **2** is slightly easier to oxidize (E\({}_{\rm ox}\) = +0.72 V vs. Fc\({}^{+}\)/Fc). Furthermore, compounds **4-6** featuring aryl substituents are \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**Compound**} & \(\lambda_{\text{abs}}\)a  & \(\varepsilon\) & **E\({}_{\text{opt}}\)b ** & \(\lambda_{\text{em}}\)c  & **\(\Phi_{\text{F}}\)d ** & **E\({}_{\text{ox}}\)e ** & **Td\({}_{10}\) \$ \$ \\ \hline
**2** & 360 & 19,000 & 3.12 & 429 & 0.75 & +0.72 & \(-\)2.73 & 203 \\
**4** & 368 & 19,000 & 3.03 & 441 & 0.86 & +0.79 & \(-\)2.63 & 290 \\
**5** & 368 & 17,000 & 3.03 & 440 & 0.68 & +0.78 & \(-\)2.68 & 318 \\
**6** & 369 & 18,000 & 3.03 & 443 & 0.76 & +0.79 & \(-\)2.66 & 385 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Photophysical and redox data. Figure 3: (a) UV-vis absorption (**top**) and fluorescence emission (**bottom**) of **2**, **4–6** in dichloromethane. (b) Calculated molecular orbitals for compound **2**. slightly easier to reduce than compound **2**. Compared to its P-congeners, compounds **2**, **4-6** present a higher band gap [12]. This is in line with the fact that linear phospholes oxides oligomers possess a smaller HOMO-LUMO gap compared to their Si analogs. The thermal stability of **2**, **4-6** was also evaluated by means of thermogravimetric (TGA) analysis and differential scanning calorimetry (DSC) in order to evaluate if these compounds can be evaporated for the construction of OLEDs. While **2** has rather moderate thermal stability (Td\({}_{10}\) = 203 \({}^{\circ}\)C, Table 1), the three aryl-substituted siloles **4-6** possess a higher stability (td\({}_{10}\) > 290 \({}^{\circ}\)C). Notably, **6** is stable up to 385 \({}^{\circ}\)C, making it an appealing candidate for insertion into optoelectronic device. Interestingly, **4** and **6**, whose optical and electrochemical properties are similar, possess different thermal properties. **4** displays the classical reversible DSC curve upon cyclization (melting up on heating and crystallization upon cooling). In the case of **6**, a melting is observed during the first heating cycle, but no crystallization and further melting are observed during the next cycles. This is typical of a glassy state, probably due to the presence of 4 alkyl chains on the fluorine moiety. Taking in account the thermal stabilities and the physical properties of compounds **2**, **4-6**, only compounds **4** and **6** were used as emitting material (EM) pure or doped in mCP matrix. In a first attempt, compound **4** (device **A**) and **6** (device **D**) were used as pure emitter in the device. The electroluminescence (EL) spectra are shown in Figure 4. The blue EL emission is red-shifted relative to the emission observed in diluted solution (Table 1). The red-shift is larger for compound **6** (29 nm) comparatively to compound **4** (15 nm). In these devices, luminance and external quantum efficiency (EQE) [45] are moderate (Table 2). However, the EL performance is larger for compound 4 relative to device **6**. It is believed that charge transport in **6** is low, causing this low efficiency.