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6-(diphenylamino)-2-naphthaldehyde
instead
of
4’-(diphenylamino)biphenyl-4-
carbaldehyde. The obtained compound was reddish solid (Yield : 45%). 1H-NMR
(300 MHz, CDCl3): δ (ppm); 8.93 (dd, J = 1.2, 7.2 Hz, 1H), 7.77–7.64 (m, 3H), 7.59–7.53
(m, 4H), 7.45 (t, J = 7.7 Hz, 1H), 7.30–7.25 (m, 4H), 7.14–7.10 (m, 5H), 7.06–7.02 (m,
3H), 6.89–6.83 (m, 2H), 2.05–2.00 (m, 4H), 0.39 (t, J = 7.2 Hz, 6H); 13C-NMR (125
MHz): δ (ppm) 158.2, 153.0, 152.6, 151.0, 148.5, 148.0, 144.6, 140.0, 135.4, 134.8, 132.8,
129.5, 128.2, 126.1, 124.5, 123.4, 122.2, 121.3, 119.8, 118.8, 117.4, 116.1, 106.8, 56.4;
FT-IR (KBr): ν = 2208, 1628, 1592, 1556, 1481, 1464, 1454, 1201, 815 cm−1; Mass (EI –
MS) m/z = 540 (M++H); HRMS calcd for C38H25N3O, 539.1998; found, 539.1992; mp:
249◦C.
2-(2-(2-(7-(diphenylamino)-9,9-diethyl-9H-fluoren-2-yl)vinyl)-4H-chromen-4-yliden
e)malononitrile (Red 3). Compound Red 3 was prepared by method of DCCPA using
6-(diphenylamino)-2-naphthaldehyde instead of 7-(diphenylamino)-9,9-diethyl-9H-
1
fluorene-2-carbaldehyde. The obtained compound was reddish solid (Yield : 84%). H
NMR (300 MHz, CDCl3): 8.91 (dd, J = 1.2, 8.4 Hz, 1H), 7.75 (t, J = 7.2 Hz, 1H),
7.68–7.62 (m, 5H), 7.57 (d, J = 7.5 Hz, 1H), 7.51 (d, J = 8.7 Hz, 2H), 7.45 (t, J = 8.4 Hz,
1H), 7.31–7.26 (m, 5H), 7.16–7.13 (m, 6H), 7.06 (t, J = 7.3 Hz, 2H), 6.88–6.79 (m, 2H),
13C-NMR (125 MHz, CDCl3) : 157.8, 153.0, 152.6, 148.2, 147.7, 143.0, 138.8, 134.9,
133.4, 129.6, 128.8, 127.9, 127.3, 126.2, 125.0, 123.6, 118.8, 118.3, 118.1, 117.0, 116.0,
107.1, 62.9, FT-IR (ATR): v (cm-1) : 2205, 1494, 1481, 1195, 700; FT-IR (KBr): ν =
2205, 1494, 1481, 1195, 700 cm−1; Mass (EI – MS) m/z = 608 (M++H); HRMS calcd for
C43H33N3O, 607.2624; found, 607.2629; mp: 276◦C.
Results and Discussion
The synthesis of Red 1 - 3 is shown in Scheme 1. Knoevenagel condensation of
the corresponding aldehyde intermediates[10–12] with 2-(2-methyl-4H-1-benzopyran-4-
ylidene)malononitrile provided red emitters 1 - 3 in moderate yield. These compounds
were fully characterized with 1H- and 13C-NMR, infrared (IR), and low- and high-resolution
mass spectrometry.
The UV-Vis absorption and PL spectra of DCCPA and Red 1 - 3 are shown in Fig. 1.
The maximum absorption peaks of DCCPA and Red 1 - 3 were observed at 452, 493, 494,
and 494 nm, respectively. The absorption of each compound showed good spectral overlap
with the emissions of the MADN in the host, indicating that MADN serves as a suitable
host in the OLEDs using DCCPA and Red 1 - 3 as red dopant materials. In the PL spectra,
the maximum emission wavelengths (λmax) of DCCPA and Red 1 - 3 appeared at 646, 681,
640, and 703 nm in the proper red region of the visible spectrum, respectively. Interestingly,
compared to DCCPA, the maximum emission peaks of Red 1 and 3 in the solution state
were red-shifted by 35 and 55 nm, respectively, due to the extended π-conjugation length
of Red 1 and 3 by the naphthalene and 9,9’-diethylfluorene spacer groups. The PL quantum
yields of Red 1 - 3 were found to be 0.31, 0.15, and 0.08, respectively, using DCCPA as
the standard. The HOMO level was measured with a photoelectron spectrometer used in a
Riken Keiki AC-2, and the LUMO level computed using the optical band gap energy and
HOMO level. The HOMO and LUMO energy levels of Red 1 - 3 were -5.36 to -5.49 eV
and -3.20 to -3.44 eV, respectively. All physical data are summarized in Table 1.
Among red emitters 1 - 3, Red 1 has the proper maximum emission peak and quan-
tum yield in the solution state for the red-emitting material. Thus, its electroluminescent
properties were explored by fabrication of a device using Red 1 as the dopant. The device
structure with the HOMO and LUMO energy levels of the materials used in the devices are