Electroluminescent zinc complexes
Russ.Chem.Bull., Int.Ed., Vol. 53, No. 10, October, 2004
2149
nylenediamine were prepared by the reactions of salicylaldeꢀ
hyde with cyclohexylamine, 4ꢀtertꢀbutylaniline, or 1,2ꢀpheꢀ
nylenediamine, respectively. Then a complex was synthesized
by the reaction of the corresponding ligand with zinc chloride in
an aqueous solution containing potassium hydroxide.
Spectral properties were measured according to a procedure
described earlier.11 Samples for measuring absorption and phoꢀ
toluminescence spectra were prepared as films deposited on a
quartz support by the same method as those for electroluminesꢀ
cence devices. IR spectra were measured for KBr pellets on a
Perkin—Elmer Spectrum BX FTIR spectrometer.
Complex Zn(OBCG)2, m.p. 196—197 °C. Found (%):
C, 66.32; H, 6.83; Zn, 13.91. C26H32N2O2Zn. Calculated (%):
C, 66.45; H, 6.86; Zn, 13.91. IR, ν/cm–1: 3086 v.w, 3043 v.w,
3022 v.w, 2933 m, 2855 w, 1614 v.s, 1538 s, 1466 s, 1447 s,
1410 m, 1363 v.w, 1340 m, 1320 m, 1307 w, 1244 v.w, 1191 m,
1149 m, 1126 w, 1075 m, 1032 w, 988 v.w, 972 v.w, 921 w,
889 w, 852 w, 814 w, 776 w, 757 m, 740 m, 663 w, 611 w,
572 v.w, 550 w, 498 w, 456 w, 422 v.w.
Results and Discussion
The absorption and photoluminescence (PL) spectra
of vacuum deposited films of the complexes under study
are presented in Fig. 1. The absorption spectra conꢀ
tain bands with maxima at 226, 245, 280, and 376 nm
(Zn(OBCG)2); 235, 311, and 410 nm (Zn(OBBA)2); 243,
297, 387, and 450 nm (Zn(OBPDA)). The maximum of
the longestꢀwave absorption band shifts to longer waveꢀ
lengths in the series Zn(OBCG)2, Zn(OBBA)2, and
Zn(OBPDA). The PL spectra were measured upon exciꢀ
tation with spectral lines corresponding to the longꢀ
wave absorption bands: λexc = 390 (Zn(OBCG)2), 406
(Zn(OBBA)2), and 460 nm (Zn(OBPDA)). The PL specꢀ
tra of the complexes under study exhibit broad (halfꢀ
width ~100 nm) bands with maxima at 453, 510, and
565 nm, respectively. The maxima of the PL bands and the
Complex Zn(OBBA)2, m.p. 257—258 °C. Found (%):
C, 78.80; H, 6.35; N, 4.93. C34H36N2O2Zn. Calculated (%):
C, 71.64; H, 6.37; N, 4.92. IR, ν/cm–1: 3070 w, 3060 w, 3025 w,
2962 m, 2929 v.w, 2866 w, 1610 v.s, 1588 v.s, 1532 s, 1509 m,
1462 s, 1441 s, 1421 v.w, 1401 w, 1389 m, 1362 w, 1354 w,
1327 m, 1310 w, 1268 v.w, 1255 v.w, 1228 v.w, 1194 w, 1177 s,
1150 s, 1127 w, 1110 w, 1030 w, 1051 w, 988 w, 944 v.w, 928 w,
911 v.w, 868 w, 839 m, 788 w, 754 m, 742 w, 621 w, 596 m,
556 w, 545 v.w, 521 w, 501 w, 479 w, 436 v.w.
Complex Zn(OBPDA), m.p. 354—355 °C. Found (%):
C, 63.44; H, 3.91; Zn, 17.10. C20H14N2O2Zn. Calculated (%):
C, 63.26; H, 3.72; Zn, 17.22. IR, ν/cm–1: 3073 w, 3014 w,
2923 w, 2854 w, 1617 v.s, 1587 s, 1531 s, 1463 s, 1446 m,
1387 m, 1351 w, 1326 m, 1245 w, 1230 v.w, 1181 s, 1153 s,
1127 m, 1109 v.w, 1049 v.w, 1032 w, 970 w, 919 m, 854 v.w,
844 v.w, 799 w, 741 s, 602 w, 551 v.w, 533 m, 511 w, 492 w,
438 v.w.
Preparation of electroluminescence devices. Glass supꢀ
ports covered with transparent conducting indium—tin oxide
In2O3—SnO2 (indium—tin oxide, ITO) were used as anodes
with a resistance of ~20 Ohm cm–2. A holeꢀtransporting layer
(mixture of triphenylamine oligomers (PTA))13 was deposited
on the anode (by pouring from a solution in benzene), or
N,N´ꢀdiphenylꢀN,N´ꢀ(3ꢀmethylphenyl)ꢀ1,1´ꢀbiphenylꢀ4,4´ꢀdiꢀ
amine (TPD)1—5 was deposited on the anode by evaporation
in vacuo. An emitting layer consisting of one of the complexes
under study was deposited on the transporting layer by evaporaꢀ
tion in vacuo. The emitting layer, being a solid solution of NR in
Zn(OBBA)2, was deposited only on PTA from a solution conꢀ
taining NR and Zn(OBBA)2 in the corresponding ratios.11 The
preparation of the device was completed by vacuum sputtering
of a metallic cathode of Al or a Mg—Ag alloy (10 : 1 wt/wt).
Procedures in vacuo were carried out at a basic pressure of
5•10–6 Torr. The surface area of the emitting part of the device
was ~5 mm2.
I (rel. units)
2.0
a
1
1.5
1.0
0.5
2
200
300
400
400
400
500
600
λ/nm
λ/nm
λ/nm
I (rel. units)
2.0
1.5
1.0
0.5
b
1
2
200
300
500
600
I (rel. units)
2.0
1.5
1.0
0.5
c
1
2
To measure the voltammetric characteristics, an enhanced
voltage from a PIꢀ50 computerꢀcontrolled potentiostat was apꢀ
plied to a sample, and the current value from the potentiostat
entered a computer through an analogꢀtoꢀdigital converter. The
brightness of EL of the device was measured with a FEUꢀ39a
photomultiplier, taking into account the geometry of the setup
and passport sensitivity of the FEU.
200
300
500
600
Fig. 1. Absorption (1) and luminescence (2) spectra of the comꢀ
plexes under study: a, Zn(OBCG)2; b, Zn(OBBA)2 (dotted curve
shows the luminescence spectrum of the Zn(OBBA)2 + 0.5%
NR system); c, Zn(OBPDA).