related mono(BODIPY) used as a reference [70], which demonstrates the advantageous synergistic effect achieved by the figure-of-eight geometry.
In an extension to this work, Nabeshima et al. have prepared several macrocycles
exhibiting pseudo-figure-of-eight geometries, through the unsymmetrical chelation
of the same bis(dipyrrin)-based macrocyclic precursor with one tetrahedral boron
atom (forming a BODIPY moiety) and one octahedral group-13 element (aluminium, gallium, or indium) [71]. Single crystal X-ray diffraction analysis showed the
presence of both enantiomers of the corresponding gallium and indium complexes in
the crystals examined; however the resolution and examination of the chiroptical
properties of these molecules is yet to be disclosed.
Chiral BODIPY Polymers
Li et al. have developed the series of linear polymers based on BODIPY and chiralBINOL 39 (Fig. 6.32) [72]. These chiral polymers, which were formed via a
Sonogashira coupling of 2,2
0 -diethynylBODIPYs with the corresponding
enantiopure 3,3
0 -diiodoBINOL derivatives, were soluble in a range of organic
solvents and exhibited red fluorescence (ϕ up to 0.26 at 622 nm for 39b in THF
solution upon visible wavelength excitation) [72]. Interestingly, mirror-image CD
spectra were obtained for the corresponding enantiomeric polymers, showing a
N
B
N
N
B
N
O
O
O
O
HN
N
N
NH
O
O
OH
OH
OH
OH
O
O
PhB(OH) 2
rac-38
(M,M)-38
(P,P)-38
g lum = -0.009
f = 0.58
g lum = +0.009
f = 0.58
Chiral HPLC
Fig. 6.31 Synthesis,
molecular structure, and
visible CPL signatures
(upon irradiation in
solution) of figure-of-eight
bis(BODIPY) 38
6 BODIPY Based Emitters of Circularly Polarized Luminescence
143