The nanoparticle aggregates afforded appreciable CPL signals at 490 nm, which
showed a shift to shorter wavelength in comparison to that in chloroform due to the
less stabilization of excimer-like state in the less polar MCH-rich solvent
(Fig. 8.15c). The dissymmetry factor |g lum | was a little enhanced to be 0.017
compared to that in molecularly dispersed state of 0.01, showing a good agreement
with the enhanced Δε value observed in the CD measurement.
UV irradiation at 365 nm to the MCH-rich solution of 2o induced the photoisomerization with the emergence of an absorption band at 650 nm corresponding to
the formation of colored isomer 2c (Fig. 8.16a). Interestingly, upon UV irradiation,
the MCH-rich solution turned turbid at room temperature, suggesting the photoinduced secondary aggregation of nanoparticles (Fig. 8.16b). The clouding behavior
was apparent in the absorption spectral change as an increase of background
scattering (Fig. 8.16a). The colored isomer 2c has a more rigid structure with an
additional covalent bond compared to 2o with a flexible conformation, leading to a
decrease in the solubility of compound in MCH-rich solutions. In comparison to the
increase in the absorption band in the visible region, the decrease of the absorption in
the UV region was more prominent. This significant decrease should be attributed to
300
400
500
Wavelength/ nm
/ M -1
cm -1
0
40
-40
L-2o
D-2o
D-2o
L-2o
(a)
(b)
400 450 500 550 600
Wavelength/ nm
CPL intensity
0
2
1
-1
-2
D-2o
L-2o
(c)
Fig. 8.15 (a) TEM image of aggregates formed by D-2o in chloroform/MCH (1:9) mixture solvent.
(b) CD spectra of 2o in chloroform (broken lines) and chloroform/MCH (1:9) mixture solvent (solid
lines). (c) CPL spectra of 2o in chloroform/MCH (1:9) mixture solvent (concentration:
1.0 Â 10
À4 M)
Fig. 8.16 (a) Absorption spectral change and (b) picture of photochromic reaction of D-2o upon
UV irradiation in chloroform/MCH (1:9) (1.0 Â 10
À4 M). (c) SEM image of aggregates formed at
the PSS of D-2 in chloroform/MCH (1:9) (1.0 Â 10
À4 M)
190
T. Nakashima and T. Kawai
showed a shift to shorter wavelength in comparison to that in chloroform due to the
less stabilization of excimer-like state in the less polar MCH-rich solvent
(Fig. 8.15c). The dissymmetry factor |g lum | was a little enhanced to be 0.017
compared to that in molecularly dispersed state of 0.01, showing a good agreement
with the enhanced Δε value observed in the CD measurement.
UV irradiation at 365 nm to the MCH-rich solution of 2o induced the photoisomerization with the emergence of an absorption band at 650 nm corresponding to
the formation of colored isomer 2c (Fig. 8.16a). Interestingly, upon UV irradiation,
the MCH-rich solution turned turbid at room temperature, suggesting the photoinduced secondary aggregation of nanoparticles (Fig. 8.16b). The clouding behavior
was apparent in the absorption spectral change as an increase of background
scattering (Fig. 8.16a). The colored isomer 2c has a more rigid structure with an
additional covalent bond compared to 2o with a flexible conformation, leading to a
decrease in the solubility of compound in MCH-rich solutions. In comparison to the
increase in the absorption band in the visible region, the decrease of the absorption in
the UV region was more prominent. This significant decrease should be attributed to
300
400
500
Wavelength/ nm
/ M -1
cm -1
0
40
-40
L-2o
D-2o
D-2o
L-2o
(a)
(b)
400 450 500 550 600
Wavelength/ nm
CPL intensity
0
2
1
-1
-2
D-2o
L-2o
(c)
Fig. 8.15 (a) TEM image of aggregates formed by D-2o in chloroform/MCH (1:9) mixture solvent.
(b) CD spectra of 2o in chloroform (broken lines) and chloroform/MCH (1:9) mixture solvent (solid
lines). (c) CPL spectra of 2o in chloroform/MCH (1:9) mixture solvent (concentration:
1.0 Â 10
À4 M)
Fig. 8.16 (a) Absorption spectral change and (b) picture of photochromic reaction of D-2o upon
UV irradiation in chloroform/MCH (1:9) (1.0 Â 10
À4 M). (c) SEM image of aggregates formed at
the PSS of D-2 in chloroform/MCH (1:9) (1.0 Â 10
À4 M)
190
T. Nakashima and T. Kawai