remained in the CD spectra after 1 min of irradiation (Fig. 8.12d). The apparent
features of these positive and negative signals at 580 nm diminished as the photoreaction proceeded after 5 min of irradiation while the sharp absorption bump was
still apparent in the absorption profile (Fig. 8.12c). This result suggests that the
preferential formation of enantiomeric coordination structure in the Ln(III)-complex
sites was effective only in the helical structure, wherein the close contact between the
complex sites is operative. The photo-induced helical to non-helical transformation
of the main framework switches off the close arrangement of the coordination units.
The labile coordination character of lanthanide ions should negate the enrichment of
enantiomeric coordination structure, diminishing the optical activity (Fig. 8.13).
8.5 Photo-Switching of CPL in Photo-Responsive
Molecular Self-Assemblies
Chiroptical properties have often been demonstrated to enhance in chiral supramolecular assemblies as supramolecular chirality [51, 52]. The CPL property was
highly dependent on the supramolecular morphologies, wherein the ordering of
building unit varies [4, 5]. Photo-responsive azobenzene units were incorporated
in a building block of a chiral supramolecular assembly (4; Fig. 8.14) [53]. (S)-(E,
E)-4 formed entangled helical fibers with a right-handed twist as a self-assembling
structure, exhibiting an intense positive CD signal at 464 nm. (R)-4 gave a similar
morphology in the self-assembling state but with opposite twist and CD signal to
Fig. 8.12 (a) Photoluminescence and (b) CPL spectral change of 3 in CHCl 3 before (broken lines)
and after photo-irradiation to achieve PSS under irradiation at 365 nm (solid lines). (c) Absorption
and (d) CD spectral change of 3(Nd) before (broken lines) and after UV irradiation (solid lines) for
1 and 5 min in CHCl 3
8 Photo-Switching of Circularly Polarized Luminescence
187
features of these positive and negative signals at 580 nm diminished as the photoreaction proceeded after 5 min of irradiation while the sharp absorption bump was
still apparent in the absorption profile (Fig. 8.12c). This result suggests that the
preferential formation of enantiomeric coordination structure in the Ln(III)-complex
sites was effective only in the helical structure, wherein the close contact between the
complex sites is operative. The photo-induced helical to non-helical transformation
of the main framework switches off the close arrangement of the coordination units.
The labile coordination character of lanthanide ions should negate the enrichment of
enantiomeric coordination structure, diminishing the optical activity (Fig. 8.13).
8.5 Photo-Switching of CPL in Photo-Responsive
Molecular Self-Assemblies
Chiroptical properties have often been demonstrated to enhance in chiral supramolecular assemblies as supramolecular chirality [51, 52]. The CPL property was
highly dependent on the supramolecular morphologies, wherein the ordering of
building unit varies [4, 5]. Photo-responsive azobenzene units were incorporated
in a building block of a chiral supramolecular assembly (4; Fig. 8.14) [53]. (S)-(E,
E)-4 formed entangled helical fibers with a right-handed twist as a self-assembling
structure, exhibiting an intense positive CD signal at 464 nm. (R)-4 gave a similar
morphology in the self-assembling state but with opposite twist and CD signal to
Fig. 8.12 (a) Photoluminescence and (b) CPL spectral change of 3 in CHCl 3 before (broken lines)
and after photo-irradiation to achieve PSS under irradiation at 365 nm (solid lines). (c) Absorption
and (d) CD spectral change of 3(Nd) before (broken lines) and after UV irradiation (solid lines) for
1 and 5 min in CHCl 3
8 Photo-Switching of Circularly Polarized Luminescence
187