structure in terms of chiral ligand orientation was the primary source as the origin of
chirality induction in 3o.
UV irradiation to a chloroform solution of 3o resulted in the emergence of an
absorption band in the visible region due to the formation of closed-ring isomer in
the photochromic framework in a similar manner to 2. The photo-reaction also
induced a decrease in the emission intensity in the whole spectral region, and the
Φ lum value dropped to 0.03 at the PSS with a conversion ratio of 85% (Fig. 8.12a).
The decrease in the emission intensity and lifetime were attributed to the Förster
resonance energy transfer (FRET) mechanism from the excited state of Eu(III) to the
photochromic center [46–48]. The photo-cyclization reaction of the photochromic
backbone of 3 also promoted a decrease in CPL intensity (Fig. 8.12b). Given that the
enantiomeric structure induced in the Eu(III) complex sites is maintained after the
photoreaction, the g lum value should be unchanged even if the CPL intensity
decreases. However, the |g lum | value decreased to <0.01, affording a large modulation amplitude in CPL dissymmetry, |Δg lum | > 0.09. The decrease in the dissymmetry factor should be attributed to the cancellation in the enrichment of one-hand
chiral coordination structure in the Eu(III) complex sites with the aid of labile
coordination character [50].
Meanwhile, UV irradiation to 3o(Nd) gave rise to an emergence of a broad
absorption band in the visible band which is superimposed with the 4I 9/2 ! 4G 5/2
transition at 580 nm in Nd(III) ion (Fig. 8.12c). This spectral change accompanies
the gradual progression of broad negative and positive CD signals over 500 nm for
D- and L-3(Nd), respectively, supporting the diastereo-selective formation of the
closed-ring isomer (c-forms). The positive and negative CD signals corresponding to
4I 9/2 ! 4G 5/2 transition band at 580 nm observed for D- and L-3o(Nd), respectively,
Fig. 8.11 (a)
Photoluminescence and (b)
CPL spectra of D-(solid
lines) and L-3o (dashed
lines) in CHCl 3
186
T. Nakashima and T. Kawai
chirality induction in 3o.
UV irradiation to a chloroform solution of 3o resulted in the emergence of an
absorption band in the visible region due to the formation of closed-ring isomer in
the photochromic framework in a similar manner to 2. The photo-reaction also
induced a decrease in the emission intensity in the whole spectral region, and the
Φ lum value dropped to 0.03 at the PSS with a conversion ratio of 85% (Fig. 8.12a).
The decrease in the emission intensity and lifetime were attributed to the Förster
resonance energy transfer (FRET) mechanism from the excited state of Eu(III) to the
photochromic center [46–48]. The photo-cyclization reaction of the photochromic
backbone of 3 also promoted a decrease in CPL intensity (Fig. 8.12b). Given that the
enantiomeric structure induced in the Eu(III) complex sites is maintained after the
photoreaction, the g lum value should be unchanged even if the CPL intensity
decreases. However, the |g lum | value decreased to <0.01, affording a large modulation amplitude in CPL dissymmetry, |Δg lum | > 0.09. The decrease in the dissymmetry factor should be attributed to the cancellation in the enrichment of one-hand
chiral coordination structure in the Eu(III) complex sites with the aid of labile
coordination character [50].
Meanwhile, UV irradiation to 3o(Nd) gave rise to an emergence of a broad
absorption band in the visible band which is superimposed with the 4I 9/2 ! 4G 5/2
transition at 580 nm in Nd(III) ion (Fig. 8.12c). This spectral change accompanies
the gradual progression of broad negative and positive CD signals over 500 nm for
D- and L-3(Nd), respectively, supporting the diastereo-selective formation of the
closed-ring isomer (c-forms). The positive and negative CD signals corresponding to
4I 9/2 ! 4G 5/2 transition band at 580 nm observed for D- and L-3o(Nd), respectively,
Fig. 8.11 (a)
Photoluminescence and (b)
CPL spectra of D-(solid
lines) and L-3o (dashed
lines) in CHCl 3
186
T. Nakashima and T. Kawai