Abstract
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 (ϕPL) 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 ϕPL of 0.62–0.72 in toluene (dielectric constant εs = 2.4), dichloromethane (εs = 9.1), acetone (εs = 21.4), and ethanol (εs = 24.3). The large pseudo-Stokes shift is distinctive considering BODIPYs with small Stokes shifts (∼500 cm–1), and the ϕPL
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.
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 (ϕPL) 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 ϕPL of 0.62–0.72 in toluene (dielectric constant εs = 2.4), dichloromethane (εs = 9.1), acetone (εs = 21.4), and ethanol (εs = 24.3). The large pseudo-Stokes shift is distinctive considering BODIPYs with small Stokes shifts (∼500 cm–1), and the ϕPL
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.
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