Osmium(II)-Based Phosphorescent Materials
Chart 1
electrochemical stability, better RGB chromaticity, and
superior luminescent quantum efficiency upon excitation.
With respect to complexes exhibiting phosphorescence at
room temperature, most investigations have been focusing
on the d6 and d8 transition metal complexes.3 The luminescent
platinum(II) d8 metal complexes, however, due to their planar
molecular geometry, may induce significant intermolecular
interaction in the solid state resulting in difficulties in
assessing their photophysical properties and hence the device
performance.4 On the other hand, both homoleptic and/or
heteroleptic coordination architectures of d6 iridium(III)
complexes have been extensively studied, showing an elegant
interplay between the photophysical properties and the
coordinated chromophores.5 In particular, octahedral iridium-
(III) systems with at least two cyclometalating chromophores
have shown much more predictable behavior for fabricating
light-emitting devices.6 As a result, versatile ligand designs
can be applied to tune excited-state properties such as
emission energy gap, lifetime, and quantum yield.
N∧NH) and osmium carbonyl reagent Os3(CO)12.1e,10 At-
tention is paid to several distinctive issues such as possible
mechanistic pathways and how to broaden reactivity patterns
using newly isolated intermediates.
Experimental Section
General Information and Materials. All reactions were per-
formed under a nitrogen atmosphere using anhydrous solvents or
solvents treated with an appropriate drying reagent. Mass spectra
were obtained on a JEOL SX-102A instrument operating in electron
impact (EI) mode or fast atom bombardment (FAB) mode. 1H and
19F NMR spectra were recorded on a Varian Mercury-400 or
INOVA-500 instrument. Elemental analyses were conducted at the
NSC Regional Instrumentation Center at National Chiao Tung
University. The nitrogen chelates, 3-(trifluoromethyl)-5-(2-pyridyl)-
pyrazole, (fppz)H, and 3-(trifluoromethyl)-5-(2-pyridyl)triazole,
(fptz)H, were prepared using methods reported in the literature.11
Preparation of 2a. A mixture of Os3(CO)12 (200 mg, 0.22 mmol)
and fppzH (141 mg, 0.66 mmol) in 25 mL of anhydrous diethylene
glycol monoethyl ether (DGME) was heated at 180 °C for 12 h.
After being cooled to room temperature, the solvent was removed
under vacuum and the residue purified using silica gel column
chromatography, eluting with a mixture of ethyl acetate (EA) and
hexane (1:1). A yellow crystalline sample of [Os3(CO)8(fppz)2] was
obtained from CH2Cl2 and methanol at room temperature; yield
72% (193 mg, 0.16 mmol).
In yet another approach, to explore the versatility of the
octahedral osmium(II) complexes, we have prepared several
luminous complexes with formulas [OsI2(CO)2(diimine)]
(diimine ) bipyridine or phenanthroline)7 and [OsX(CO)3-
(chelate)] (X ) halide or pseudohalide; chelate is, for
example, a substituted â-diketonate8 or quinolinolate anion).9
Three representative structural drawings are depicted in Chart
1, for which the accompanying studies have clearly unraveled
the nature of the excited states that gave the bright
phosphorescence at room temperature. In this paper, we
present a comprehensive approach to extend the previously
documented reactions involving pyridylazoles (denoted as
Spectral data for 2a: MS (FAB, 192Os) m/z 1224 (M+); IR
(C6H12) ν(CO), 2079 (s), 2012 (vs), 1996 (vs), 1970 (w), 1944 (s)
cm-1; 1H NMR (500 MHz, acetone-d6, 294 K) δ 9.25 (d, 1H, JHH
(3) (a) Vogler, A.; Kunkely, H. Top. Curr. Chem. 2001, 213, 143. (b)
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Chem. ReV. 2005, 249, 1360. (c) Browne, W. R.; O’Boyle, N. M.;
McGarvey, J. J.; Vos, J. G. Chem. Soc. ReV. 2005, 34, 641.
(4) (a) Lai, S.-W.; Che, C.-M. Top. Curr. Chem. 2004, 241, 27. (b) Ma,
B.; Li, J.; Djurovich, P. I.; Yousufuddin, M.; Bau, R.; Thompson, M.
E. J. Am. Chem. Soc. 2005, 127, 28. (c) Lu, W.; Chan, M. C. W.;
Zhu, N.; Che, C.-M.; Li, C.; Hui, Z. J. Am. Chem. Soc. 2004, 126,
7639. (d) Kavitha, J.; Chang, S.-Y.; Chi, Y.; Yu, J.-K.; Hu, Y.-H.;
Chou, P.-T.; Peng, S.-M.; Lee, G.-H.; Tao, Y.-T.; Chien, C.-H.; Carty,
A. J. AdV. Funct. Mater. 2005, 15, 223. (e) Chang, S.-Y.; Kavitha, J.;
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Shu, C.-F. Inorg. Chem. 2005, 44, 7770.
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) 5.0 Hz), 8.16 (td, 1H, JHH ) 8.0, 1.0 Hz), 8.04 (d, 1H, JHH
)
8.0 Hz), 7.64 (ddd, 1H, JHH ) 6.3, 6.0, 1.5 Hz), 7.14 (s, 1H); 19F
NMR (470 MHz, acetone-d6) δ -57.5 (s). Anal. Calcd for
C26H10F6N6O8Os3: C, 25.62; N, 6.98; H, 0.83. Found: C, 25.87;
N, 6.84; H, 0.81.
Preparation of 2b. Similar to the procedure described for 2a,
this product was prepared using Os3(CO)12 (200 mg, 0.22 mmol)
and fptzH (142 mg, 0.66 mmol). Yellow crystals of [Os3(CO)8-
(fptz)2] were obtained by recrystallization from a mixture of CH2-
Cl2 and methanol; yield 60% (161 mg, 0.13 mmol).
Spectral data for 2b: MS (FAB, 192Os) m/z 1226 (M+); IR
(C6H12) ν(CO), 2083 (w), 2015 (vs), 2000 (s), 1976 (w), 1949 cm-1
;
1H NMR (500 MHz, acetone-d6, 294 K) δ 9.39 (d, 1H, JHH ) 5.5
Hz), 8.32 (td, 1H, JHH ) 8.0, 1.5 Hz), 8.11 (d, 1H, JHH ) 8.0 Hz),
7.88 (ddd, 1H, JHH ) 6.3, 5.5, 1.5 Hz); 19F NMR (470 MHz,
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Inorganic Chemistry, Vol. 45, No. 25, 2006 10189