0.45
0.40
0.35
0.30
0.25
(a)
(b)
1.0
0.8
0.6
0.4
0.2
0.0
Initial
600 hrs
1200 hrs
1200 hrs
600 hrs
Initial
0.25 0.30 0.35
0.40 0.45
400
500
600
700
800
x
Wavelength (nm)
Figure 4. a) EL spectra of DBN-based white LED before thermal aging and after thermal aging at 120 °C for 300 and 1200 h and b) the change of the
CIE color coordinates.
Optical properties of the white LED such as color temperature, color
rendering index, and the CIE color coordinates were evaluated under
a forward bias current of 10 mA at room temperature. An integrating
sphere was used for the measurement.
demonstrate that an organic LUCO with an appropriate struc-
ture could replace phosphors for LED applications. The ther-
mally stable dye-bridged nanohybrid potentially allows for new
white LED designs, instead of inorganic phosphor-based LEDs,
for straightforward fabrication of better performance lighting.
Supporting Information
Supporting Information is available from the Wiley Online Library or
from the author.
Experimental Section
Synthesis of DCM-OH: 4-(diethylamino)salicylaldehyde (6.71 mmol)
was dissolved with tetrahydrofuran with potassium hydroxide and stirred
with 6-bromo-1-hexanol (6.71 mmol) for 12 h. Both (2,6-dimethyl-4H-
pyran-4-ylidene)malononitrile (6.1 mmol) and piperidine (6.1 mmol)
were mixed with the above precursor in the presence of acetonitrile
30 mL. The reaction mixture was refluxed for 3 h. Methanol was added
to precipitate the crude product from the reaction solution. DCM-OH
was obtained by washing the precipitate with MeOH/CHCl3 (4/1) three
times.
Acknowledgements
This work was supported by the National Research Foundation of
Korea(NRF) grant funded by the Korea government(MEST) (No. 2011-
0017971) and by grant No. EEWS-2010-N01100426 from EEWS Research
Project of the office of KAIST EEWS Initiative.
Synthesis of DBA: DCM-OH was then mixed with 3-(triethoxysilyl)-
propyl isocyanate in a 1:2 molar ratio. The mixture was stirred at 80 °C
for 6 h to promote a urethane reaction between the isocyanate group in
3-(triethoxysilyl)propyl isocyanate and the hydroxyl group of DCM-OH.
Finally, DBA-R was obtained. DBA-G was synthesized from 2,5-diamino-
3,6-dicyanopyrazine (DADCP, 8.01 mmol) and (3-aminopropyl)-
trimethoxysilane (16.02 mmol). They were mixed and stirred at 70 °C for
24 h. Amidine was formed through reaction between the cyano group of
DADCP and the amino group of (3-aminopropyl)trimethoxysilane.
Fabrication of DBO and DBN: DBO was synthesized by reacting the pre-
paredDBA,2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane(ECTS,0.108mol),
and diphenylsilanediol (DPSD, 0.075 mol) via non-hydrolytic sol-gel
condensation. Barium hydroxide monohydrate was used as a catalyst
for this reaction. The DBA and ECTS were mixed and the DPSD was
continuously added to the mixture solution to prevent self-condensation.
The DBA concentration was controlled to have between 0.05 mmol L−1
to 5 mmol L−1 in the DBO. The reaction was completed after 4 h at 80 °C
under a nitrogen atmosphere. The DBN was prepared by polymerization
of DBO at 150 °C for 2 h using hexahydro-4-methylphthalic anhydride as
a hardener and tetrabutylphosphonium methanesulfonate as an initiator
to fabricate solid-state samples.
Received: August 11, 2011
Revised: September 23, 2011
Published online: November 7, 2011
[1] S. Nakamura, G. Fasol, The Blue Laser Diode: GaN Based Light Emit-
ters and Lasers, Springer, Berlin 1996, pp. 216–221.
[2] R. J. Xie, N. Hirosaki, Sci. Technol. Adv. Mater. 2007, 8, 588.
[3] S. Neeraj, N. Kijima, A. K. Cheetham, Chem. Phys. Lett. 2004, 387, 2.
[4] a) R. J. Xie, N. Hirosaki, M. Mitomo, K. Sakuma, N. Kiumra, Appl.
Phys. Lett. 2006, 89, 241103; b) R. J. Xie, N. Hirosaki, N. Kiumra,
K. Sakuma, M. Mitomo, Appl. Phys. Lett. 2007, 90, 191101.
[5] a) O. Huyal, U. Koldemir, T. Ozel, H. V. Demir, D. Tuncel, J. Mater.
Chem. 2008, 18, 3568; b) F. Hide, P. Kozodoy, S. P. DenBaars,
A. J. Heeger, Appl. Phys. Lett. 1997, 70, 2664; c) C. Zhang,
A. J. Heeger, J. Appl. Phys. 1998, 84, 1579; d) L. Zhang, B. Li,
B. Lei, Z. Hong, W. Li, J. Lumin. 2008, 128, 67; e) G. Heliotis,
P. N. Stavrinou, D. D. C. Bradley, E. Gu, C. Griffin, C. W. Jeon,
M. D. Dawson, Appl. Phys. Lett. 2005, 87, 103505; f) H. Kim, J. Jin,
Y. Lee, S. Lee, C. Hong, Chem. Phys. Lett. 2006, 431, 341.
[6] a) S. Chhajed, Y. Xi, Y. L. Li, Th. Gessmann, E. F. Schubert, J. Appl.
Phys. 2005, 97, 054506; b) Y. Xi, E. F. Schubert, Appl. Phys. Lett.
2004, 85, 2163.
Characterization: UV-vis absorption spectra of the synthesized DBN
were obtained using a Shimadzu UV-3101 PC spectrophotometer.
Photoluminescence (PL) spectra of the DBN were collected on a DARSA
PRO 5100 PL System (PSI Trading Co., Ltd., Korea) at room temperature
using a xenon lamp (500 W) as an excitation source. Quantum yields
of DBO were determined relative to DCM in 1-propanol (0.57) and
rhodamine 6G in ethanol (0.95).[10]
[7] K. Shirai, A. Yanagisawa, H. Takahashi, K. Fukunishi, M. Matsuoka,
Dyes Pigments 1998, 39, 49.
[8] S. C. Yang, J. S. Kim, J. H. Jin, S. Y. Kwak, B. S. Bae, J. Appl. Polym.
Sci. 2010, 117, 2140.
©
wileyonlinelibrary.com
Adv. Mater. 2011, 23, 5767–5772
2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
5771