quinine solution, “filtered” by a s-PS film sorbed–desorbed with (R)- and (S)carvone (Fig. 10.13c). The dissymmetry factor is somehow related to the apparent
CD signal of the s-PS film in the emissive spectroscopic region of the fluorescent
solution and it is thus of extrinsic origin.
In conclusion, s-PS films with induced chirality, due to sorption–desorption of
chiral molecules, exhibit chiroptical properties that resemble those of liquid crystals
or polyfluorene films studied in the literature (see, for example, Refs. [78, 83, 84]).
The behavior is reminiscent of metamaterials constituted of intrinsically chiral holes,
since CD signals do not significantly change with rotation of the film around a
perpendicular axis [85]. Besides that, also considering change of front and back sides
of the film, little variations occur, so cross terms between linear birefringence and
linear dichroism [63, 86] do not seem important enough to explain the observed
behavior. The observation of a broad CD band, in absence of a real absorption band,
is strongly suggestive of possible different reflection/scattering of right and left
circularly polarized light, as observed/hypothesized, for example, in Ref. [87], and
proved on polyfluorene films by Meskers [84] with an ad hoc instrumental setup.
This experience hints at possible applications of chiral polymer films coupled with
light emitting devices—the advantage for s-PS treated with volatile chiral species
being that one has no need to add chiral units by chemical synthesis. This experience
suggests similar strategies to obtain and testing materials generating CPL [88].
10.3 Concluding Remarks
CPL is a thrilling phenomenon that has still a high degree of novelty and deserves
attention and concerted efforts from theoreticians and experimentalists. The first
ones will help in finding adequate protocols to improve the description of luminescence from singlet excited states and to find new ways of dealing with phosphorescence phenomena from triplet excited states of chiral molecules; finally, an effort
toward a better description of metal ions in chiral complexes is desirable. The
experimentalists are expected to synthesize new molecular systems as well as to
discover complex systems, like polymers, fibrils, or mesoscopic systems, where CPL
is co-present with other chiroptical phenomena to be disentangled from.
References
1. Emeis CA, Oosterhoff LJ (1967) Emission of circularly polarized radiation by optically active
compounds. Chem Phys Lett 1:129–132
2. Dekkers HPJM, Emeis CA, Oosterhoff LJ (1969) Measurement of optical activity in racemic
mixtures. J Am Chem Soc 91:4590–4590
3. Schippers PH, van den Beukel A, Dekkers HPJM (1982) An accurate digital instrument for the
measurement of circular polarisation of luminescence. J Phys E Sci Instrum 15:945–950
10 Structural and Electronic Information Drawn. . .
243
CD signal of the s-PS film in the emissive spectroscopic region of the fluorescent
solution and it is thus of extrinsic origin.
In conclusion, s-PS films with induced chirality, due to sorption–desorption of
chiral molecules, exhibit chiroptical properties that resemble those of liquid crystals
or polyfluorene films studied in the literature (see, for example, Refs. [78, 83, 84]).
The behavior is reminiscent of metamaterials constituted of intrinsically chiral holes,
since CD signals do not significantly change with rotation of the film around a
perpendicular axis [85]. Besides that, also considering change of front and back sides
of the film, little variations occur, so cross terms between linear birefringence and
linear dichroism [63, 86] do not seem important enough to explain the observed
behavior. The observation of a broad CD band, in absence of a real absorption band,
is strongly suggestive of possible different reflection/scattering of right and left
circularly polarized light, as observed/hypothesized, for example, in Ref. [87], and
proved on polyfluorene films by Meskers [84] with an ad hoc instrumental setup.
This experience hints at possible applications of chiral polymer films coupled with
light emitting devices—the advantage for s-PS treated with volatile chiral species
being that one has no need to add chiral units by chemical synthesis. This experience
suggests similar strategies to obtain and testing materials generating CPL [88].
10.3 Concluding Remarks
CPL is a thrilling phenomenon that has still a high degree of novelty and deserves
attention and concerted efforts from theoreticians and experimentalists. The first
ones will help in finding adequate protocols to improve the description of luminescence from singlet excited states and to find new ways of dealing with phosphorescence phenomena from triplet excited states of chiral molecules; finally, an effort
toward a better description of metal ions in chiral complexes is desirable. The
experimentalists are expected to synthesize new molecular systems as well as to
discover complex systems, like polymers, fibrils, or mesoscopic systems, where CPL
is co-present with other chiroptical phenomena to be disentangled from.
References
1. Emeis CA, Oosterhoff LJ (1967) Emission of circularly polarized radiation by optically active
compounds. Chem Phys Lett 1:129–132
2. Dekkers HPJM, Emeis CA, Oosterhoff LJ (1969) Measurement of optical activity in racemic
mixtures. J Am Chem Soc 91:4590–4590
3. Schippers PH, van den Beukel A, Dekkers HPJM (1982) An accurate digital instrument for the
measurement of circular polarisation of luminescence. J Phys E Sci Instrum 15:945–950
10 Structural and Electronic Information Drawn. . .
243