## 4 Conclusions  
New sky-blue-light-emitting materials were synthesized by introducing a bulky side group into fused chromophore with anthracene and spirofluorene; these compounds have high LE. The TP-AFF-TP device showed a CIE value of (0.25, 0.45) and achieved an LE of 2.55 cd/A at an applied current density of 10 mA/cm\({}^{2}\). The TP-ASF device demonstrated a notable LE of 5.17 cd/A at 10 mA/cm\({}^{2}\), along with a CIE value of (0.17, 0.31). The results revealed that TP-ASF exhibited superior LE and a more favorable CIE value compared to TP-AFF-TP. These results show that when a side group is substituted into the fused core, it is better for the high efficiency to use the electron lobe position of core moiety. Furthermore, TP-ASF displays excellent solubility in commonly used organic solvents due to its highly twisted molecular structure. The white OLED device fabricated using the solution process with TP-ASF achieved a LE of 3.13 cd/A and a PE of 2.69 lm/W. Especially, the CIE value and the EL spectra were (0.30, 0.34) and 463, 549 nm, which are matched with the color of lighting application. The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/app131810154/s1](https://www.mdpi.com/article/10.3390/app131810154/s1)]([https://www.mdpi.com/article/10.3390/app131810154/s1](https://www.mdpi.com/article/10.3390/app131810154/s1)), Table S1: Time-dependent density functional theory calculations; Figure S1: DSC curve (a) TP-AFF-TP, (b) TP-ASF; Figure S2: Device lifetime of TP-AFF-TP and TP-ASF; Figure S3: \({}^{1}\)H-NMR Spectrum of 5-Bromoanthraquinone (**1**); Figure S4: \({}^{1}\)H-NMR Spectrum of 1-Bromoanthracene (**2**); Figure S5: \({}^{1}\)H-NMR Spectrum of 1-(2-Bromohenyl)anthracene (**4**); Figure S6: \({}^{1}\)H-NMR Spectrum of 2,7-Dibromo-spiro-fluorene[3,4]naphthalene (**5**); Figure S7: \({}^{1}\)H-NMR Spectrum of Spiro-fluorene[3,4]naphthalene (**6**); Figure S8: \({}^{1}\)H-NMR Spectrum of Spiro-fluorene[3,4]-5-bromoanthane (**7**); Figure S9: \({}^{1}\)H-NMR Spectrum of 2,7-Bis-[1,1'3',1\"]phenyl-spiro-fluorene[3,4]naphthalene (TP-AFF-TP); Figure S10: \({}^{13}\)C-NMR Spectrum of 2,7-Bis-[1,1',3',1\"]phenyl-spiro-fluorene[3,4]naphthalene (TP-AFF-TP); Figure S11: \({}^{1}\)H-NMR Spectrum of Spiro-fluorene[3,4]-5-terphenylnaphthalene (TP-ASF); Figure S12: \({}^{13}\)C-NMR Spectrum of Spiro-fluorene[3,4]-5-terphenylnaphthalene (TP-ASF). Conceptualization, S.K. and J.P.; Methodology, S.P. (Sangwook Park); Validation, S.P. (Sangwook Park), S.K. and S.P. (Sunwoo Park); Formal analysis, S.P. (Sangwook Park), H.L., K.L. ([PERSON]) and J.P.; Investigation, S.K., S.P. ([PERSON]) and H.K. ([PERSON]); Resources, J.P.; Writing-original draft, S.P. (Sangwook Park); Writing-review & editing, H.L., K.L. and J.P.; Visualization, H.K. and H.L. ; Supervision, J.P.; Project administration, J.P.; Funding acquisition, J.P. All authors have read and agreed to the published version of the manuscript. This research was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (2020R1A6A1A03048004). This work was supported by the Technology Innovation Program (20017422, Development of raw materials and process for ArF-i photoresist) funded By the Ministry of Trade, Industry & Energy (MOTIE, Republic of Korea). This work was supported by the Technology Innovation Program (20017832, Development of TiN-based electrode materials and ALD equipment for 10-mm DRAM capacitor electrode deposition process) funded By the Ministry of Trade, Industry & Energy (MOTIE, Korea). This work was partly supported by the GRRC program of Gyeonggi province [(GRRCKYUNGHE2023-B01), Development of ultra-fine process materials based on the sub-nanometer class for the next-generation semiconductors]. This research was supported by Basic Science Research Capacity Enhancement Project through Korea Basic Science Institute (National research Facilities and Equipment Center) grant funded by the Ministry of Education (No.