Angewandte
Communications
Chemie
Table 1: Photophysical data of tungsten(VI) complexes at room temperature.
Absorption
The lowest energy absorption band
for 1a–j is at 400–427 nm (e = 2.3–
Emission
3
ꢀ1
ꢀ1
3
ꢀ1
3
ꢀ1 [a]
[a]
[a,b]
labs [nm] (e [ꢀ10 mol dm cm ])
lem [nm] (t [ms]) F [%]
7.9 ꢁ 10 m cm ) in dichlorome-
thane while for 2a–f an intense
absorption band is observed for
each complex at 375–396 nm (e =
1
1
1
1
a
b
c
243 (sh, 32.1), 271 (sh, 17.8), 301 (sh, 9.4), 345 (sh, 3.0), 400 (3.6) 595 (14.6)
248 (sh, 20.1), 275 (sh, 14.1), 312 (sh, 6.7), 362 (sh, 2.1), 415 (2.3) 625 (10.0)
0.3
0.2
0.3
2.8
240 (sh, 30.7), 308 (sh, 8.2), 358 (sh, 2.8), 418 (2.9)
243 (35.1), 273 (sh, 17.6), 299 (sh, 12.6), 400 (3.8)
618 (16.4)
600 (96.9)
3
ꢀ1
ꢀ1
d
4.5–13.4 ꢁ 10 m cm ). These low
energy absorption bands with high
e values are insensitive to solvent
polarity (Supporting Information,
Figures S5 and S6) and are assigned
to intraligand (IL) transitions. This
assignment is consistent with the
DFT/TDDFT calculations at the
[
c]
[c]
580
22
1
1
1
1
1
1
2
2
2
2
e
f
g
h
i
245 (22.1), 283 (sh, 11.7), 312 (sh, 8.5), 417 (2.3)
248 (37.6), 297 (sh, 10.1), 413 (3.2)
246 (41.4), 274 (sh, 17.3), 297 (sh, 11.0), 414 (3.7)
244 (23.7), 274 (sh, 12.7), 293 (sh, 8.1), 413 (2.9)
271 (25.0), 312 (sh, 23.6), 330 (sh, 28.6), 349 (29.5), 427 (7.9)
266 (25.1), 327 (29.3), 348 (28.2), 426 (7.7)
263 (47.5), 375 (7.1)
258 (37.5), 385 (4.5)
287 (59.3), 396 (10.5)
284 (62.1), 390 (11.6)
657 (25.7)
622 (77.9)
623 (56.2)
639 (37.2)
598 (62.0)
600 (16.0)
490, 585 (75.9)
515, 600 (10.4)
515, 614 (42.0)
513, 616 (62.0)
0.8
1.6
1.0
1.4
2.1
0.6
0.3
0.1
1.2
0.8
j
a
b
c
d
optimized ground state (S ) geome-
0
tries (see DFT calculations in the
Supporting Information).
[
c]
[c]
508, 646
2.5
1.2
0.4
All of these complexes display
photoluminescence at room tem-
perature (Table 1; Supporting Infor-
mation, Figure S3) with emission
quantum yields (F) in the range of
0.1–2.8% in dichloromethane solu-
tions and up to 22% in thin film at
room temperature. Complexes 1a–
2
2
e
f
283 (89.2), 382 (13.4)
262 (43.5), 283 (41.7), 292 (42.0), 383 (9.0)
501, 602 (25.4)
520, 598 (12.7)
[a] Dichloromethane solutions. [b] Emission quantum yields (F) were measured with [Ru(bpy) ][PF6]2
3
(
bpy=2,2’-bipyridine; F=0.062) in degassed acetonitrile as a standard reference. [c] Absolute
emission quantum yields of thin-film samples were measured with a Hamamatsu Quantaurus-QY
Absolute PL quantum yields spectrometer C11347. 5 wt% in mCP thin film.
1
j display orange to red emission at
5
95–657 nm with a shoulder at 500–560 nm in dichlorome-
thane solution (Figure 2; Supporting Information, Figures S7
and S8). The lifetimes of the 595–657 nm emission are in the
microsecond regime (10–97 ms) and the radiative decay rate
2
ꢀ1
constants (k ) lie in the range of 1.8–3.8 ꢁ 10 s . The
r
excitation spectra for 1a–j agree well with the absorption
spectra of the corresponding complexes. Varying the solvent
polarity does not induce any significant shift in emission lmax
(
Supporting Information, Figure S10). The orange–red emis-
3
sion is assigned to a IL excited state. In the solid state, the
emission blue-shifts to 540–652 nm at 298 K (Supporting
Information, Table S3).
For 2a–f, dual fluorescence–phosphorescence are
observed with emission lmax values at 490–520 nm (high
energy (HE); t < 0.1 ms) and at 585–616 nm (low energy
(LE); t = 10–76 ms; Figure 2b). The HE emission band is
insensitive to oxygen whereas the LE emission band is
strongly quenched under aerated condition (see 2e in the
Supporting Information, Figure S12; see 2c in Figure 6). This
leads to a change in emission color from orange to green. The
1
HE and LE emission bands are assigned to IL fluorescence
3
and IL phosphorescence of the quinolinolate ligands, respec-
tively. Varying the solvent polarity results in only little change
in the wavelength of the HE and LE bands of 2e (within
ꢀ1
4
00 cm ; Supporting Information, Figure S11). The HE
emission is more intense than the LE emission when there
is no aryl substituent on the quinolinolate (Qin) ligand (2a
and 2b) but the trend is reversed for 2c–2 f when the Qin
ligand has aryl substituents on the 5- and 7-position.
The emission properties of 1d and 2d in thin films have
been examined. The emission maximum of 1d in 1,3-
bis(carbazol-9-yl)benzene (mCP) thin film (5 wt%) is at
580 nm and is insensitive to complex concentration; the
Figure 2. UV/Vis absorption and emission spectra of a) 1a, 1d, 1i, 1j,
and b) 2a–f at room temperature, measured in degassed dichloro-
methane solutions.
2
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2016, 55, 1 – 6
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