## 3 Results and Discussion
### Electroluminescence Properties  
The subsequent configuration of the nondoped device was used utilizing the synthesized materials: ITO/2-TNATA (60 nm)/NPB (15 nm)/TP-AFF-TP or TP-ASF (35 nm)/Alq\({}_{3}\) (20 nm)/LiF (1 nm)/Al (200 nm). The EL performance and electrical properties are shown in Table 2 and Figure 4. The operating voltage of TP-ASF was approximately 0.9V lower than that of TP-AFF-TP. This can be attributed to the fact that in the band diagram, the hole injection from NPB and electron injection from Alq3 are more facile in TP-ASF than in TP-AFF-TP (see Figure 5a). The LE (cd/A) and power efficiency (PE) (Im/W) of the TP-ASF devices was high compared to TP-AFF-TP. TP-AFF-TP and TP-ASF exhibit luminance efficiencies of 2.55 cd/A and 5.17 cd/A, respectively, along with power efficiencies of 1.03 Im/W and 2.39 Im/W, respectively. IQE values of TP-AFF-TP and TP-ASF were 11 and 22%, respectively, in the solution state and 5 and 13%, respectively, in the film state. The external quantum efficiency (EQE) values of TP-AFF-TP and TP-ASF were 1.06 and 2.80%, respectively. All EL efficiencies of TP-ASF were higher than that of TP-AFF-TP. It might be that the side groups were substituted at the positions two and seven of spirofluorene, which has small electron density distribution, and at the position nine of anthracene, which has relatively large electron density distribution, as shown in Figure 3. As a result, TP-ASF, which has the side group on the electron-rich position, showed higher efficiency than TP-AFF-TP. These results show that the side group location, which is a connected core moiety, is important for an increase in the EL efficiency of the emitting material [25]. In addition, CIE values are (0.25, 0.45) and (0.17, 0.31) in cases of TP-AFF-TP and TP-ASF, respectively. This means TP-ASF had high color purity for blue by low CIEy value compared to TP-AFF-TP because introduced TP at anthracene effectively prevented \(\pi\)-\(\pi\) stacking. The reason why the EL maximum value is different from the PL maximum value is that the recombination zone under the device operation is not located at the center of the emitting layer inside. In order to solve this issue, we need to change the kind of hole-transporting layer (HTL) or electron-transporting layer (ETL) as well as the various thicknesses of HTL or ETL. Further studies on the engineering device regarding the different carrier transporting layers are underway. We will report it separately. Regarding the device lifetime (LT), the LT50 of TP-AFF-TP and TP-ASF were approximately 40 min and 1 h at 1000 nit, respectively. It is expected that the lifetime of the device would be increased if the charge balance were improved by applying different carrier transport materials based on the various thicknesses (Figure S2). Figure 3: Electron density distribution of HOMO and LUMO in TP-AFF-TP and TP-ASF (calculated by the DFT/B3 LYP/6-31G(d) for molecule optimization). Recently, there has been a notable emphasis on solution-processed white OLEDs (WOLEDs) within the realms of OLED backlighting and lighting applications. The synthesized materials could be good candidates for solution processing. Based on the highly twisted molecular structure, it can increase the solubility in organic solvent. For example, a binapthhyl structure with a twisted backbone along an auxiliary axis exhibits good solubility, even in the case of polymers having a binapthhyl moiety [26]. Especially TP-ASF, which showed high efficiency in nondoped devices, was used as a blue dopant for WOLED. The  
Figure 4: OLED device performance of TP-AFF-TP and TP-ASF emitters: (**a**) current-voltage-luminescence curve, (**b**) current efficiency and power efficiency according to the current density, (**c**) EQE and (**d**) EL spectra at 10 mA/cm\({}^{2}\); and device photos of TP-AFF-TP (top) and TP-ASF (bottom). Figure 5: Device structure with the energy-level diagrams of (**a**) non-doped devices for TP-AFF-TP and TP-ASF, (**b**) white OLED using TP-ASF.