Combined Effects of Stereoisomeric and Steric Factors on Electronic and Photophysical Properties of Bis-cyclometalated Ir(III) Complexes Containing 2,5-Diaryl-1,3,4-oxadiazole Based and Picolin

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• 作者：Gahungu Godefroid ; Su Juanjuan ; Liu Yuqi ; Qu Xiaochun ; Si Yanling ; Shang Xiaohong ; Wu Zhijian
• 刊名：The Journal of Physical Chemistry C
• 出版年：2012
• 出版时间：July 12, 2012
• 年：2012
• 卷：116
• 期：27
• 页码：14575-14583
• 全文大小：438K
• 年卷期：v.116,no.27(July 12, 2012)
• ISSN：1932-7455

文摘

Electronic structure methods based on DFT and TDDFT were applied to understand the recently reported unusual photophysical properties for a series of cyclometalated iridium complexes of 2,5-diaryl-1,3,4-oxadiazole (oxdⁿ) based and picolinate ligands. Under the hypotheses of possible steric and stereoisomeric effects on the electronic and photophysical properties, both the N,N-trans and N,N-cis types of complexes bearing oxdⁿ ligands of different twisting degree were considered. On the basis of the results herein, an explanation of the experimental observations was attempted, according to which complexes Ir(oxd¹)₂(pic) (1) [oxd¹ = 2-(4-fluorophenyl)-5-(2,4,6-tri-tert-butylphenyl)-1,3,4-oxadiazole and pic = picolinate] and Ir(oxd²)₂(pic) (2) [oxd² = 2-(4-fluorophenyl)-5-(2,4,6-triisopropylphenyl)-1,3,4-oxadiazole] show an extremely poor quantum phosphorescence efficiency (桅_PL < 1%). The poor 桅_PL was shown not to be inherent to spin鈥搊rbit coupling effects, but determined by the intersystem crossing (ISC) rate, which was found to be tightly linked to the twisting degree of the oxdⁿ ligands, and to the stereoisomeric factor. The results evidenced a large S₁鈥揟₁ splitting energy (螖E_S1-T1) estimated at 0.81 and 0.72 eV (for 1 and 2, respectively) and a drastically small S₀鈫扴₁ transition dipole (渭_S1) estimated at 0.26 and 0.32 D, comparatively to 0.38 eV and 2.76 D of 螖E_S1-T1 and 渭_S1 values for the N,N-trans Ir(oxd³)₂(acac) complex [with oxd³ = 2-(4-fluorophenyl)-5-(2,4,6-triisopropylphenyl)-1,3,4-oxadiazole and acac = acetyl acetone] showing a 桅_PL of 44% [Chem. Commun. 2007, 1352], due to the structural isomerism and to the twisting degree of the oxdⁿ ligand, respectively. Accordingly, we were able to explain the reported unusual photophysical properties of 2 and 1.