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Deuterated Reagents for Electronics
The hydrogen/deuterium isotope effect of the host material on the lifetime of organic light-emitting diodes:
The hydrogen/deuterium primary kinetic isotope effect provides useful information about the degradation mechanism of OLED host materials. Thus, replacement of labile C–H bonds in the host with C–D bonds increases the device lifetime by a factor of five without loss of efficiency, and replacement with C–C bonds by a factor of 22.5. Organic light-emitting diodes (OLEDs) being innovative devices for display and illumination, their device lifetime and hence the mechanism of device degradation remain the most pressing subjects of research. Many of the studies reported thus far have focused on the analysis of the degradation products, while a few have reported on the kinetics of the molecular processes of the degradation.

We focused on the hydrogen/deuterium (H/D) primary kinetic isotope effect (KIE) as a mechanistic probe, where the rate of a chemical reaction slows down by a factor of 6.5 (a theoretical value at 298 K)8 when the cleavage of the C–H(D) bond in question is the rate determining step in the overall reaction sequence. We report here and finding that deuteration of the benzylic methyl groups in a green phosphorescent host material (i.e., CH3 CZBDF vs. CD3CZBDF in Fig. 1a) increases the device lifetime by a factor of five (from 0.2 h to 1.0 h) without affecting the other properties of the device much. This rate retardation factor of five is consistent with the KIE value reported for the heterolysis of a benzylic C–H bond. Taking together the isotope effect and the resonance-stabilizing effect of a furan ring (Fig. 1b), we consider the degradation of the methyl group in CH3CZBDF to be involved as a critical step of the degradation process; that is, the molecule is oxidized to a radical cation (i.e., hole formation) during operation of the OLED device and suffers from the loss of either a proton or a hydrogen radical. Guided by this analysis, we replaced the heterolytically labile C–H bonds in CH3CZBDF with more stable C–CH3 bonds (t-BuCZBDF) and found the lifetime to increase by a factor of 22.5 under the same device configuration. The lifetime enhancement by a factor of five through H to D change in the OLED performance makes an interesting contrast to a reported decrease of solar cell performance by 50% where no C–H(D) cleavage is involved. These data indicate that isotope effects are of considerable practical and mechanistic values in organic electronic research.
Compounds
CS-T-16663 Deuterium Oxide
CS-T-53699 Dimethyl Sulfoxide D6
CS-T-71953 Methanol D4
CS-T-62117 Toluene D8
CS-CE-00812 Trifluoroacetic acid D
CS-O-11242 Benzene D6
CS-T-46994 Acetone D6
CS-T-50737 Chloroform D
CS-O-15142 Sodium deuteroxide
CS-O-13174 Sulfuric Acid D2
Application of Deuterium in OLED:
  1. Deuterium increases the lifetime of the Organic light-emitting diodes (OLEDs) device by a factor of five to 20 without significantly affecting other properties of the device
  2. Deuteration of specific molecular layers is used to study morphology, diffusion and interfacial behavior in organic thin-film semiconducting devices.
  3. The lifetime increases in combination with high quantum efficiency and good color saturation.
  4. The deuterated compounds have greater air tolerance than the non-deuterated analogs. This can result in greater processing tolerance both for the preparation and purification of the materials and in the formation of electronic devices using the materials.
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