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Light-Induced Structural Change in Iridium Complexes Studied by Electron Spin Resonance.
A Batagin-Neto1, A P Assis2, J F Lima3
1Campus Experimental de Itapeva, UNESP - Univ Estadual Paulista , Rua Geraldo Alckmin 519, Itapeva, São Paulo 18409-010, Brazil.
The Journal of Physical Chemistry. A
|May 10, 2014
Summary
Investigating iridium complexes like FIrpic and Ir(ppy)3 using electron spin resonance (ESR) revealed UV light induces paramagnetic states. These states, linked to charge transfer, are thermally activated, offering insights into organometallic compound stability.
Area of Science:
- Organometallic Chemistry
- Materials Science
- Photophysics
Background:
- Iridium complexes are crucial for high-efficiency organic light-emitting diodes (OLEDs).
- Their application is limited by poor stability, often due to poorly understood photodegradation.
- Understanding excited states is key to improving device longevity.
Purpose of the Study:
- To investigate UV-induced paramagnetic states in iridium complexes (FIrpic and Ir(ppy)3).
- To elucidate the mechanisms behind photodegradation in these materials.
- To determine the thermal stability of photoinduced states.
Main Methods:
- Electron Spin Resonance (ESR) spectroscopy was employed.
- Experiments were conducted on iridium(III) bis[(4,6-fluorophenyl)-pyridinato-N,C2']picolinate (FIrpic) and iridium(III)-tris(2-phenylpyridine) (Ir(ppy)3) complexes.
- Temperature-dependent decay measurements and electronic structure calculations were performed.
Main Results:
- UV photoexcitation generated paramagnetic states in the iridium complexes.
- Strong hyperfine interactions indicated matrix/complex charge-transfer processes.
- Photoinduced centers exhibited thermal activation with energy barriers of 0.3–0.6 eV.
- Calculations suggested observed ESR signals correspond to distorted, metastable, negatively charged iridium complexes.
Conclusions:
- Charge-transfer processes are responsible for UV-induced paramagnetic states in iridium complexes.
- These states are thermally activated, providing a pathway for degradation.
- The findings offer insights into the stability mechanisms of iridium-based materials for OLEDs.
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