Dissymmetric Bis(dipyrrinato)zinc(II) Complexes: Rich Variety and Bright Red to Near-Infrared Luminescence with a Large Pseudo-Stokes Shift

详细信息    查看全文

• 作者：Ryota Sakamoto ; Toshiki Iwashima ; Julius F. Kögel ; Shinpei Kusaka ; Mizuho Tsuchiya ; Yasutaka Kitagawa ; Hiroshi Nishihara
• 刊名：Journal of the American Chemical Society
• 出版年：2016
• 出版时间：May 4, 2016
• 年：2016
• 卷：138
• 期：17
• 页码：5666-5677
• 全文大小：684K
• 年卷期：0
• ISSN：1520-5126

文摘

Bis(dipyrrinato)metal(II) and tris(dipyrrinato)metal(III) complexes have been regarded as much less useful luminophores than their boron difluoride counterparts (4,4-difluoro-4-bora-3a,4a-diaza-s-indacenes, BODIPYs), especially in polar solvent. We proposed previously that dissymmetry in such metal complexes (i.e., two different dipyrrinato ligands in one molecule) improves their fluorescence quantum efficiencies. In this work, we demonstrate the universality and utility of our methodology by synthesizing eight new dissymmetric bis(dipyrrinato)zinc(II) complexes and comparing them with corresponding symmetric complexes. Single-crystal X-ray diffraction analysis, ¹H and ¹³C NMR spectroscopy, and high-resolution mass spectrometry confirm the retention of dissymmetry in both solution and solid states. The dissymmetric complexes all show greater photoluminescence (PL) quantum yields (ϕ_PL) than the corresponding symmetric complexes, allowing red to near-infrared emissions with large pseudo-Stokes shifts. The best performance achieves a maximum PL wavelength of 671 nm, a pseudo-Stokes shift of 5400 cm^–1, and ϕ_PL of 0.62–0.72 in toluene (dielectric constant ε_s = 2.4), dichloromethane (ε_s = 9.1), acetone (ε_s = 21.4), and ethanol (ε_s = 24.3). The large pseudo-Stokes shift is distinctive considering BODIPYs with small Stokes shifts (∼500 cm^–1), and the ϕ_PL values are higher than or comparable to those of BODIPYs fluorescing at similar wavelengths. Electrochemistry and density functional theory calculations illustrate that frontier orbital ordering in the dissymmetric complexes meets the condition for efficient PL proposed in our theory.