## 3 Results and Discussion
### Photophysical and Electrochemical Properties  
The photophysical properties of DAA compounds **1-3** were investigated by UV-Vis absorption and photoluminescence (PL) spectroscopy (Figure 2 and Table 1). The absorption spectra of **1-3** in dichloromethane (1.0 \(\times\) 10\({}^{-5}\) M) displayed the typical \(\pi\pi\)* vibronic transition patterns (\(\lambda_{\text{abs}}\) = 365, 384, and 405 nm for **1** and \(\lambda_{\text{abs}}\) = 367, 386, and 407 nm for **2** and **3**, Table 1) derived from the isolated anthracene moieties. The absorption maximum point (\(\lambda_{\text{abs}}\)) of **2** and **3** was slightly red-shifted by ca. 2 nm compared to that of compound **1**. These features were also shown in the fluorescence spectra of each compound. The emission maxima (\(\lambda_{\text{em}}\)) of **1-3** were observed at 429 nm for **1** and 439 nm for **2** and **3** (Table 1), respectively. Accordingly, the red-shifted spectra of **2** and **3** distinctively implied that both the naphthyl and biphenyl moiety had a slightly stronger electron-donating property than the phenyl group and, thus, could induce the narrow band gaps. The band gaps estimated from the absorption edge for **2** and **3** were indeed slightly narrower than that of **1** (2.93 eV for **2** or **3** and 2.98 eV for **1**, Table 1). Furthermore, the PL spectra of all compounds were similar to the previously reported DAA derivatives (Figure 2) [44] assignable to the lowest \(\pi\pi\)* transition on the anthracene units. ITO/NPB (40 nm)/**1**, **2**, or **3** (30 nm, DPAVBi (8 wt %))/Alq\({}_{3}\) (30 nm)/LiF (0.5 nm)/Al (100 nm) device, where ITO is the anode; NPB is the HTL; the chemically purified anthracene derivatives **1**, **2** or **3** (host) and DPAVBi (dopant) served as the emission layer (EML); Alq\({}_{3}\) was the electron transport layer (ETL); and a thin LiF served as the electron injection layer at the Al cathode interface. Figure 5a shows the EL spectra of the OLEDs using **1-3** with a DPAVBi dopant. All devices exhibited the expected blue emissions and their main EL peaks were commonly observed at 488 and 512 nm with a shoulder peak at 556 nm. The peak intensity at 512 nm was somewhat higher than the reported EL features of DPAVBi, which was attributed to the slight emission from Alq\({}_{3}\). The maximum EL peak was observed at 488 nm for **1** and **2** and at 512 nm for **3** because of the increased Alq\({}_{3}\) emission originating from the inefficient charge transport to the EML in **3**-based OLEDs. Figure 5b shows the measured \(L\)-\(V\) characteristics of the **1-3**-based OLEDs with an 8 wt % ratio of DPAVBi. At 10 V, the **1-3**-based OLEDs showed an \(L\) of 2153.5, 243.0, and 156.3 cd\(\cdot\)m\({}^{-2}\), respectively. The inset shows the measured \(J\)-\(V\) characteristics of the OLEDs. Moreover, at 10 V, the **1-3**-based OLEDs presented a \(J\) of 91.6, 16.4, and 13.2 mA\(\cdot\)cm\({}^{-2}\), respectively. We defined the turn-on and operating voltages as the voltages providing the \(L\) of 1 and 100 cd\(\cdot\)m\({}^{-2}\). As a result, the turn-on voltage of the **1-3**-based OLEDs was 6.0, 7.8, and 8.5 V, while the operating voltage was 7.4, 9.4, and 9.8 V, respectively. The current efficiency of **1-3**-based OLEDs at the operating voltage was 2.1, 1.4, and 1.1 cd A\({}^{-1}\), respectively. Meanwhile, the power efficiency of the **1-3**-based OLEDs at the operating voltage was 0.9, 0.5, and 0.4 lm\(\cdot\)W\({}^{-1}\). Combining the \(J\)-\(V\)-\(L\) characteristics and the EL spectra, the external quantum efficiency (EQE) of the **1-3**-based OLEDs at the operating voltage was calculated as 0.8%, 0.5%, and 0.4%. The Commission Internationale de l'Eclairage (CIE) color coordinates for **1-3** appeared at (0.25, 0.51), (0.25, 0.51), and (0.27, 0.52), respectively. Table 2 summarizes the measured device parameters. These results clearly indicated that the **1**-based OLEDs showed superior charge transport and light emission abilities among all devices.