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Table 2 Photophysical properties of 1, 2, Cu(LMe)Br, and Cu(LiPr)Br in
2-MeTHF
In conclusion, highly emissive three-coordinate thiolate
copper(I) complexes were obtained in good yields. The change
in orientation of the –SPh-containing aryl ring is found to
dramatically alter the optical properties of 1 and 2 in solution.
Application of 1 and 2 in TADF-type OLEDs is now in progress.
This work was supported by the Japan Society of the Promo-
tion of Science (Grant-in-Aid for Scientific Research; No.
25410080). We acknowledge Dr Daisuke Hashizume for
technical assistance with X-ray structural analysis.
lmaxa/nm (tb/ms)
FPL
c
T = 293 K
T = 77 K
T = 293 K
T = 77 K
1
2
592 (1.4)
546 (1.0)
523 (4.2)
519 (7.7)
466 (1300)
492 (2300)
506 (1900)
501 (1000)
0.24
0.15
0.40
0.50
0.95
0.95
0.93
0.90
Cu(LMe)Brd
Cu(LiPr)Brd
a
c
Emission maximum; lexc = 355 nm. b Emission decay time; lexc = 355 nm.
Absolute PL quantum yield in solution (error Æ 5%). d For comparison.
Notes and references
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Fig. 4 Optimized core structures of 1 in the singlet (left) and the triplet
(center) excited state and the ground state (right); dihedral angles, and
S1 and T1 energies of each optimized structure.
MO calculations indicate that the structural change was
based on the rotation of the –SPh-containing aryl ring
about the axis of the Cu–S bond (see the inset in Fig. 3). As
represented in Fig. 4, the calculations provide confirmation of
the lowering of energies of the S1 and T1 states, which are
responsible for the red-shift of the emission peaks; the metal
plane and the aryl ring, which are coplanar in the ground state
(S0), are perpendicular to each other in S1 and T1 states (dihedral
angles between the metal plane and aryl ring are 91.11). However,
the trigonal planar core structure, which consists of Cu(I), sulfur,
and two phosphorous atoms, remains unchanged even in the
excited states, suggesting that this structural change is different
from a Jahn–Teller type distortion observed in trigonal planar Au(I)
complexes.6 Small S1–T1 energy gaps (605 cmÀ1 and 830 cmÀ1, see
Fig. 4) in both the optimized structures suggest that the orange
emission observed is due to TADF. The S1 energy obtained by MO
calculations for 1 is in good accord with the peak energy at 293 K
(Fig. 4 and Table 2). In comparison with 1, 2 does not exhibit a large
red-shift (54 nm, as seen in Table 2) probably because the aryl ring
cannot turn to the orthogonal position owing to the bulky iPr
groups on the metal side (see Fig. S7 in the ESI†). Furthermore, we
found that three-coordinated copper(I) complexes Cu(LMe)Br and
Cu(LiPr)Br do not show large red-shift of emission by warming from
77 K to 293 K (Table 2). This result strongly supports the assump-
tion that luminescence color alteration is due to orientation change
of the thiolate aryl ring.
6 K. A. Barakat, T. R. Cundari and M. A. Omary, J. Am. Chem. Soc., 2003,
125, 14228–14229.
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