**2.1. EL spectra of OLEDs based on Zn(PSA-BTZ)2**

Figure 2 shows the EL spectra of Zn(PSA-BTZ)2 in two electroluminescence devices: device D1, ITO/PTA/NPD/Zn(PSA-BTZ)2/Al:Ca, (Figure 2a, curve 1) and device D2, ITO/PTA/Zn(PSA-BTZ)2/AlCa, (Figure 2b, curve 1). For comparison, curve 2 in Figure 2a shows the PL spectrum of Zn(PSA-BTZ)2 powder.

**Figure 2.** Spectra of Zn(PSA-BTZ)2 in the devices D1 to D5. (a): EL spectrum of the device D1 ITO/PTA/NPD/Zn(PSA-BTZ)2/Al:Ca (1); PL spectrum of Zn(PSA-BTZ)2 powder (2); EL spectrum of the device D3 ITO/PTA/NPD/CBP/Zn(PSA-BTZ)2/Al:Ca (3); EL spectrum of the device D5 ITO/PEDOT:PSS/Zn(PSA-BTZ)2/Al:Ca (4) (b): EL spectrum of the device D2 ITO/PTA/Zn(PSA-BTZ)2/AlCa (1); EL spectrum of the device D4 ITO/PTA/CBP/Zn(PSA-BTZ)2/AlCa (2)

The EL spectrum of device D1 contains two bands with maxima at 460 and 560 nm. Maximum of the first band is close to that of the PL peak of Zn(PSA-BTZ)2 powder at 450 nm and may be attributed to the intrinsic luminescence of Zn(PSA-BTZ)2. The second peak may be probably due to exciplex formation between NPD and Zn(PSA-BTZ)2. For device D2, the EL spectrum exhibits only wide band with a maximum at 553 nm, which may be attributed to exciplex formation between PTA and Zn(PSA-BTZ)2. Exciplex can be formed between the ground state of a donor molecule and the excited state of an acceptor molecule [12]. In our case, the donor molecule is presented by NPD or PTA, and the acceptor molecule by Zn(PSA-BTZ)2 complex. Exciplex band corresponds to the transition from the excited state of the acceptor and the ground state of the donor and has lower transition energy compared to the intrinsic emission band corresponding to the transition between the excited and ground state of the acceptor molecule [7-10,12].

### **2.2. EL spectra of OLEDs based on Zn(TSA-BTZ)2**

180 Organic Light Emitting Devices

to 3 V and brightness of 103 cd/m2 at 10 V.

**2.1. EL spectra of OLEDs based on Zn(PSA-BTZ)2** 

shows the PL spectrum of Zn(PSA-BTZ)2 powder.

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the device is determined by the hole-transporting material, which is in contact with the zinc complex. The devices are typically characterized by bias voltages of light appearance about 2.5

Figure 2 shows the EL spectra of Zn(PSA-BTZ)2 in two electroluminescence devices: device D1, ITO/PTA/NPD/Zn(PSA-BTZ)2/Al:Ca, (Figure 2a, curve 1) and device D2, ITO/PTA/Zn(PSA-BTZ)2/AlCa, (Figure 2b, curve 1). For comparison, curve 2 in Figure 2a

**Figure 2.** Spectra of Zn(PSA-BTZ)2 in the devices D1 to D5. (a): EL spectrum of the device D1

device D3 ITO/PTA/NPD/CBP/Zn(PSA-BTZ)2/Al:Ca (3); EL spectrum of the device D5 ITO/PEDOT:PSS/Zn(PSA-BTZ)2/Al:Ca (4) (b): EL spectrum of the device D2 ITO/PTA/Zn(PSA-

BTZ)2/AlCa (1); EL spectrum of the device D4 ITO/PTA/CBP/Zn(PSA-BTZ)2/AlCa (2)

ITO/PTA/NPD/Zn(PSA-BTZ)2/Al:Ca (1); PL spectrum of Zn(PSA-BTZ)2 powder (2); EL spectrum of the

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Figure 3 shows the EL spectra of Zn(TSA-BTZ)2 in the electroluminescence devices: (a) device D6, ITO/PTA/NPD/Zn(TSA-BTZ)2/Al:Ca, (b) device D7, ITO/PTA/Zn(TSA-BTZ)2/AlCa and device D12, ITO/PTA/CBP/Zn(TSA-BTZ)2/Al:Ca. The PL spectrum of Zn(TSA-BTZ)2 powder is shown for comparison (Figure 3a, curve 2).

For the devices D6 and D7, intensive exciplex EL bands are observed in the yellow region with the maxima around 585 nm. Only a weak shoulder in the region of the intrinsic Zn(TSA-BTZ)2 emission at about 460 nm is observed. For device D7, the EL spectra are shown for different bias voltages from 3.5 to 6.0 V. The spectra are normalized to obtain equal intensities of exciplex bands for all voltages. A small continuous growth of intrinsic emission relative intensity is observed. A small blue shift of exciplex band maximum from 585 nm at 3.5 V to 575 nm at 6.0 V is also observed. This is in contrast with previously reported strong dependence of EL bands positions on bias voltages [11,49,50] where field induced shift of EL band of about 50 nm could be attributed to the overlap of the emission from different excited states. As showed Kalinowski et al. [51], the field dependence of EL spectrum in such systems is a result of electric field mediated interplay among localized (monomolecular) excitons, exciplexes, and electroplexes in conjunction with their specific environment. For the device D12, no exciplex band is observed which is discussed in section 4.

### **2.3. EL spectra of OLEDs based on Zn(POPS-BTZ)2**

Figure 4 shows the EL spectra of Zn(POPS-BTZ)2 in the devices D8 ITO/PTA/NPD/Zn(POPS-BTZ)2/Al:Ca (curves 1) and D9 ITO/PTA/NPD/CBP/Zn(POPS-BTZ)2/Al:Ca (curve 3). The PL spectrum of Zn(POPS-BTZ)2 powder (curve 2) is shown for comparison. Strong exciplex band in the green region with the maximum at about 540 nm and shoulder at about 460 nm due to intrinsic emission of Zn(POPS-BTZ)2 is observed in the

EL spectra of the device D8. The normalized EL spectra are shown for different bias voltages from 4.0 to 6.0 V. A small continuous growth of intrinsic emission relative intensity and a small blue shift of exciplex band maximum from 545 nm at 4.0 V to 535 nm at 6.0 V are also observed. For the device D9, no exciplex band is observed which is discussed in section 4.

Exciplex Electroluminescence of the New Organic Materials for Light-Emitting Diodes 183

**Figure 4.** Spectra of Zn(POPS-BTZ)2 based devices: Normalized EL spectra of the device D8

ITO/PTA/NPD/CBP/Zn(POPS-BTZ)2/Al:Ca (3)

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**2.4. EL spectra of OLEDs based on Zn(DFP-SAMQ)2**

and hole-transporting material (curve 4) which is discussed in section 3.

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**Figure 5.** Spectra of Zn(DFP-SAMQ)2 based devices: EL spectra of the devices D10

Zn(DFP-SAMQ)2 powder (3) and of PTA:Zn(DFP-SAMQ)2 mixed film (4).

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ITO/PTA/NPD/Zn(DFP-SAMQ)2/AlCa (1) and D11 ITO/PTA/Zn(DFP-SAMQ)2/AlCa (2); PL spectra of

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ITO/PTA/NPD/Zn(POPS-BTZ)2/Al:Ca for bias voltages 4.0 V (blue curve), 4.5, 5.0, 5.5 V (black curves) and 6.0 V (red curve) (1), PL of Zn(POPS-BTZ)2 powder (2) and the EL spectrum of the device D9

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Figure 5 shows the EL spectra of Zn(DFP-SAMQ)2 in the devices D10 ITO/PTA/NPD/Zn(DFP-SAMQ)2/AlCa (curve 1) and D11 ITO/PTA/Zn(DFP-SAMQ)2/AlCa (curve 2). For comparison, the PL spectrum of Zn(DFP-SAMQ)2 powder with maximum at 465 nm is shown (curve 3). Exciplex bands with maxima at about 560 nm and no intrinsic emission are observed in the EL spectra both for devices with both PTA and PTA/NPD hole-transporting layers. Exciplex emission can also be observed in the PL spectra of the films containing blends of zinc complex

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**Figure 3.** Normalized EL spectra of the devices based on Zn(TSA-BTZ)2 and the PL spectrum of Zn(TSA-BTZ)2 powder. (a): Normalized EL spectrum of the device D6 ITO/PTA/NPD/Zn(TSA-BTZ)2/Al:Ca (1) and the PL spectrum of Zn(TSA-BTZ)2 powder (2); (b): Normalized EL spectra of the device D7 ITO/PTA/Zn(TSA-BTZ)2/Al:Ca for bias voltages 3.5 V (blue curve), 4.0, 4.5, 5.0, 5.5 V (black curves) and 6.0 V (red curve) (1) and normalized EL spectrum of the device D12 ITO/PTA/CBP/Zn(TSA-BTZ)2/Al:Ca (2).

**Figure 4.** Spectra of Zn(POPS-BTZ)2 based devices: Normalized EL spectra of the device D8 ITO/PTA/NPD/Zn(POPS-BTZ)2/Al:Ca for bias voltages 4.0 V (blue curve), 4.5, 5.0, 5.5 V (black curves) and 6.0 V (red curve) (1), PL of Zn(POPS-BTZ)2 powder (2) and the EL spectrum of the device D9 ITO/PTA/NPD/CBP/Zn(POPS-BTZ)2/Al:Ca (3)

#### **2.4. EL spectra of OLEDs based on Zn(DFP-SAMQ)2**

182 Organic Light Emitting Devices

BTZ)2/Al:Ca (2).

EL spectra of the device D8. The normalized EL spectra are shown for different bias voltages from 4.0 to 6.0 V. A small continuous growth of intrinsic emission relative intensity and a small blue shift of exciplex band maximum from 545 nm at 4.0 V to 535 nm at 6.0 V are also observed. For the device D9, no exciplex band is observed which is discussed in section 4.

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**Figure 3.** Normalized EL spectra of the devices based on Zn(TSA-BTZ)2 and the PL spectrum of Zn(TSA-BTZ)2 powder. (a): Normalized EL spectrum of the device D6 ITO/PTA/NPD/Zn(TSA-BTZ)2/Al:Ca (1) and the PL spectrum of Zn(TSA-BTZ)2 powder (2); (b): Normalized EL spectra of the device D7 ITO/PTA/Zn(TSA-BTZ)2/Al:Ca for bias voltages 3.5 V (blue curve), 4.0, 4.5, 5.0, 5.5 V (black curves) and 6.0 V (red curve) (1) and normalized EL spectrum of the device D12 ITO/PTA/CBP/Zn(TSA- Figure 5 shows the EL spectra of Zn(DFP-SAMQ)2 in the devices D10 ITO/PTA/NPD/Zn(DFP-SAMQ)2/AlCa (curve 1) and D11 ITO/PTA/Zn(DFP-SAMQ)2/AlCa (curve 2). For comparison, the PL spectrum of Zn(DFP-SAMQ)2 powder with maximum at 465 nm is shown (curve 3). Exciplex bands with maxima at about 560 nm and no intrinsic emission are observed in the EL spectra both for devices with both PTA and PTA/NPD hole-transporting layers. Exciplex emission can also be observed in the PL spectra of the films containing blends of zinc complex and hole-transporting material (curve 4) which is discussed in section 3.

**Figure 5.** Spectra of Zn(DFP-SAMQ)2 based devices: EL spectra of the devices D10 ITO/PTA/NPD/Zn(DFP-SAMQ)2/AlCa (1) and D11 ITO/PTA/Zn(DFP-SAMQ)2/AlCa (2); PL spectra of Zn(DFP-SAMQ)2 powder (3) and of PTA:Zn(DFP-SAMQ)2 mixed film (4).
