In:
ChemPhysChem, Wiley, Vol. 21, No. 20 ( 2020-10-16), p. 2320-2326
Abstract:
The inter‐ligand energy transfer (ILET) process in heteroleptic iridium complex, [Ir(dfppy) 2 (bpy‐Im 2 )] + , where dfppy =2‐(2,4‐difluorophenyl)pyridine and bpy‐Im 2 =4,4’‐bis(1,2‐diphenyl‐1H‐benzo[d]imidazole)‐2,2’,‐bipyridine, was investigated using a femtosecond transient absorption (fs‐TA) spectroscopic technique. The photophysical properties of [Ir(dfppy) 2 (bpy‐Im 2 )] + with significantly expanding π‐conjugated ligand are compared to those of [Ir(dfppy) 2 (bpy)] + ( bpy =2,2’‐bipyridine) and a free bpy‐Im 2 ligand. The emission spectrum of [Ir(dfppy) 2 (bpy‐Im 2 )] + shows no shift upon changing the solvent polarity, whereas the free ligand bpy‐Im 2 showed bathochromic fluorescence shifts with increasing solvent polarity, which is attributed to intramolecular charge transfer (ICT). The unique photophysical properties of [Ir(dfppy) 2 (bpy‐Im 2 )] + are due to the fast ILET process from 3 MLCT dfppy to 3 MLCT/ 3 LC bpy‐Im2 , resulting in the phosphorescence emission originating from 3 MLCT/ 3 LC bpy‐Im2 . On the other hand, the TA bands of bpy‐Im 2 are observed at 540 and 480 nm, corresponding to the singlet and triplet manifolds, respectively. In contrast, the TA spectrum of [Ir(dfppy) 2 (bpy‐Im 2 )] + showes broad bands centered at 420 and 600 nm, attributed to the transitions from 3 MLCT dfppy and 3 MLCT/ 3 LC bpy‐Im2 , respectively. Time‐resolved spectroscopic results confirm the efficient ILET dynamics from 3 MLCT dfppy to 3 MLCT/ 3 LC bpy‐Im2 in [Ir(dfppy) 2 (bpy‐Im 2 )] + . From the relaxation times determined by singular value decomposition analysis and simple sequential kinetic model, we infer that the ILET process from 3 MLCT dfppy to 3 MLCT/ 3 LC bpy‐Im2 occurs with a time constant of ca. 4 ps. The presented results in this study show that the introduction of an expanding π‐conjugated ligand can lead to the efficient ILET dynamics for improving the OLED performance.
Type of Medium:
Online Resource
ISSN:
1439-4235
,
1439-7641
DOI:
10.1002/cphc.202000565
Language:
English
Publisher:
Wiley
Publication Date:
2020
detail.hit.zdb_id:
2025223-7
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