Details

Autor(en) / Beteiligte

• Song, Yi-Hwa
• Chiu, Yuan-Chieh
• Chi, Yun
• Cheng, Yi-Ming
• Lai, Cheng-Hsuan
• Chou, Pi-Tai
• Wong, Ken-Tsung
• Tsai, Ming-Han
• Wu, Chung-Chih

Titel

Phosphorescent Iridium(III) Complexes with Nonconjugated Cyclometalated Ligands

Ist Teil von

• Chemistry : a European journal, 2008-06, Vol.14 (18), p.5423-5434

Ort / Verlag

Weinheim: WILEY-VCH Verlag

Erscheinungsjahr

2008

Quelle

Wiley Online Library - AutoHoldings Journals

Beschreibungen/Notizen

• A series of blue phosphorescent iridium(III) complexes 1–4 with nonconjugated N‐benzylpyrazole ligands were synthesized and their structural, electrochemical, and photophysical properties were investigated. Complexes 1–4 exhibit phosphorescence with yields of 5–45 % in degassed CH2Cl2. Of the compounds, 1 showed emission that was nearly true blue at 460 nm with a lack of vibronic progression. These photophysical data clearly demonstrate that the methylene spacer of the cyclometalated N‐benzylpyrazole chelate effectively interrupts the π conjugation upon reacting with a third L^X chelating chromophore. This gives a feasible synthesis for the blue phosphorescent complexes with a sufficiently large energy gap. In another approach, these complexes were investigated for their suitability for the host material in phosphorescent OLEDs. The device was synthesized by using 1 as the host for the green‐emitting [Ir(ppy)3] dopant, which exhibits an external quantum conversion efficiency (EQE) of up to 11.4 % photons per electron (and 36.6 cdA−1), with 1931 Commission Internationale de L'Eclairage (CIE) coordinates of (0.30, 0.59), a peak power efficiency of 21.7 lmW−1, and a maximum brightness of 32000 cdm−2 at 14.5 V. At the practical brightness of 100 cdm−2, the efficiency remains above 11 % and 18 lmW−1, demonstrating its great potential as the host material for phosphorescent organic light‐emitting diodes. True blue: The nonconjugated nature of a methylene spacer interrupts the π conjugation of the cyclometalated ligands, which lowers the π orbital energies and destabilizes the respective π* orbitals. Incorporation of a third chelating chromophore with a blue‐light energy gap induces true‐blue‐light emission at room temperature (see figure).