(Fig. 6.31). This structure was obtained with an 88% chemical yield, as a racemic
mixture, by reacting the corresponding bis(dipyrrin)-based macrocyclic precursor
with phenylboronic acid (Fig. 6.31) [70]. In such a chelation process, the figure-ofeight helicity was achieved by the tetrahedral geometry imposed by the requirement
for tetrahedral boron coordination. Optical resolution by chiral HPLC provided the
corresponding M,M and P,P enantiomers, which exhibited an intense red fluorescence (λ max ¼ 655 nm, ϕ ¼ 0.58 in CHCl 3 ) and mirror-image CPL spectra with a
maximum |g lum | value of 9Á10
À3 (positive for the P,P isomer) in CHCl 3 solution
upon visible wavelength excitation. This results in a chiroptical efficiency (ϕÁ|g lum |)
value of 5.3Á10
À3 , which is one of the highest values reported for a CPL-SOMs to
date [70]. Noticeably, the |g lum | value is three times higher than that exhibited by a
Fig. 6.30 CPL (upper curves; R,R enantiomers in blue, S,S in red) and total luminescence (lower
curves) spectra of 36 (left) and 37 (right) in CHCl 3 solution upon visible excitation [reproduced with
permission from [62], copyright 2016 WILEY-VCH Verlag GmbH
142
M. J. Hall and S. de la Moya