these helicenic-mono(BODIPY) designs, those based on C 2 -symmetric BINOLbased N,N,O,O-boron-chelated dipyrromethane (spiranic mono(O-BODIPY)) have
proven interesting due to both synthetic accessibility [50, 52, 53] and their
chiroptical versatility, notably their ability to modulate their fluorescence signatures,
including the CPL sign, by simple manipulation of the ICT probability [54]. However, these simple chiral mono(BODIPY)s have yet to yield particularly high |g lum |
values, with no CPL-SOM mono(BODIPY) to date exceeding |g lum | ¼ 10
À2 . This is
likely a consequence of the difference in magnitude of the magnetic (m) and electric
(μ) transition dipole moments in CPL-SOMs of this nature; thus future chiral mono
(BODIPY) designs will have to carefully manage these key parameters. Interestingly
Mori et al. have surveyed the chiroptical properties of the known CPL active mono
(BODIPY)s and have shown a good linear correlation between |g lum | and |g abs |
(absolute luminescent and absorption dissymmetry factors, respectively) [73],
suggesting that rapid evaluation of CPL emission in chiral mono(BODIPY)s may
be possible through simple CD measurement. However, it should be noted that
correlation of |g lum | with |g abs | became less linear when more flexible bis(BODIPY)s
were included in the analysis, suggesting more complex photophysical behaviours,
including conformational changes between the S 0 and S 1 states, in these systems. In
the related poly(BODIPY)s, several bis(BODIPY)-based designs have been
explored in an attempt to introduce the required efficient chiral perturbation for
CPL emission. The to-date published chiral bis(BODIPY) molecular architectures
have included direct bonding of two BODIPY cores around a conformationally
restricted axis (i.e. axially chiral bis(BODIPY)s) [34], indirect bonding via a flexible
chiral linker to gain chiral helicity (i.e. helically labile bis(BODIPY)s) [62], and
construction of macrocyclic figure-of-eight geometries involving N,N,O,O-boronchelated dipyrromethane [70]. In particular, the figure-of-eight design has resulted in
some of the highest reported values of |g lum | % 10
À2
, suggesting that multichromophoric systems may be required in the development of bright CPL-SOM
BODIPYs. Usefully, some of these BODIPY-based chiral designs, aimed to chirally
perturb the inherently achiral BODIPY fluorophore, have been shown to operate in
other related achiral fluorophores to endow them with CPL activity [74–78], especially when such a fluorophore is closely related to BODIPY (e.g. azaBODIPYs or
BOPHYs) [76–78].
References
1. Sanchez-Carnerero EM, Agarrabeitia AR, Moreno F, Maroto BL, Muller G, Ortiz MJ, de la
Moya S (2015) Circularly polarized luminescence from simple organic molecules. Chem Eur J
21:13488–13500
2. Kumar J, Nakashima T, Kawai T (2015) Circularly polarized luminescence in chiral molecules
and supramolecular assemblies. Phys Chem Lett 6:3445–3452
3. Jan C-M, Lee Y-H, Wu K-C, Lee C-K (2011) Integrating fault tolerance algorithm and
circularly polarized ellipsometer for point-of-care applications. Opt Express 19:5431–5441
6 BODIPY Based Emitters of Circularly Polarized Luminescence
145
proven interesting due to both synthetic accessibility [50, 52, 53] and their
chiroptical versatility, notably their ability to modulate their fluorescence signatures,
including the CPL sign, by simple manipulation of the ICT probability [54]. However, these simple chiral mono(BODIPY)s have yet to yield particularly high |g lum |
values, with no CPL-SOM mono(BODIPY) to date exceeding |g lum | ¼ 10
À2 . This is
likely a consequence of the difference in magnitude of the magnetic (m) and electric
(μ) transition dipole moments in CPL-SOMs of this nature; thus future chiral mono
(BODIPY) designs will have to carefully manage these key parameters. Interestingly
Mori et al. have surveyed the chiroptical properties of the known CPL active mono
(BODIPY)s and have shown a good linear correlation between |g lum | and |g abs |
(absolute luminescent and absorption dissymmetry factors, respectively) [73],
suggesting that rapid evaluation of CPL emission in chiral mono(BODIPY)s may
be possible through simple CD measurement. However, it should be noted that
correlation of |g lum | with |g abs | became less linear when more flexible bis(BODIPY)s
were included in the analysis, suggesting more complex photophysical behaviours,
including conformational changes between the S 0 and S 1 states, in these systems. In
the related poly(BODIPY)s, several bis(BODIPY)-based designs have been
explored in an attempt to introduce the required efficient chiral perturbation for
CPL emission. The to-date published chiral bis(BODIPY) molecular architectures
have included direct bonding of two BODIPY cores around a conformationally
restricted axis (i.e. axially chiral bis(BODIPY)s) [34], indirect bonding via a flexible
chiral linker to gain chiral helicity (i.e. helically labile bis(BODIPY)s) [62], and
construction of macrocyclic figure-of-eight geometries involving N,N,O,O-boronchelated dipyrromethane [70]. In particular, the figure-of-eight design has resulted in
some of the highest reported values of |g lum | % 10
À2
, suggesting that multichromophoric systems may be required in the development of bright CPL-SOM
BODIPYs. Usefully, some of these BODIPY-based chiral designs, aimed to chirally
perturb the inherently achiral BODIPY fluorophore, have been shown to operate in
other related achiral fluorophores to endow them with CPL activity [74–78], especially when such a fluorophore is closely related to BODIPY (e.g. azaBODIPYs or
BOPHYs) [76–78].
References
1. Sanchez-Carnerero EM, Agarrabeitia AR, Moreno F, Maroto BL, Muller G, Ortiz MJ, de la
Moya S (2015) Circularly polarized luminescence from simple organic molecules. Chem Eur J
21:13488–13500
2. Kumar J, Nakashima T, Kawai T (2015) Circularly polarized luminescence in chiral molecules
and supramolecular assemblies. Phys Chem Lett 6:3445–3452
3. Jan C-M, Lee Y-H, Wu K-C, Lee C-K (2011) Integrating fault tolerance algorithm and
circularly polarized ellipsometer for point-of-care applications. Opt Express 19:5431–5441
6 BODIPY Based Emitters of Circularly Polarized Luminescence
145