300
S. Kobatake and T. Nakahama
S
S
Et
Et
F
F
F
F
F
F
S
S
Et
Et
F
F
F
F
F
F
Vis.
UV
O O
O O
O O
O O
S
S
Me
Me
S
S
Me
Me
F
F
F
F
F
F
Vis.
UV
S
S
Me
Me
F
F
F
F
F
F
S
S
Me
Me
F
F
F
F
F
F
Vis.
UV
F
F
F
F
F
F
(i)
(ii)
(iii)
1a
Fluorescent
(λ f = 485 nm, Φ f = 0.017)
1b
Non-fluorescent
2a
Non-fluorescent
3b
Fluorescent
(λ f = 630 nm, Φ f = 0.0001)
2b
Fluorescent
(λ f 550 nm, Φ f = 0.87)
3a
Fluorescent
(λ f = 430 nm, Φ f = 0.012)
Φ o→c = 0.42
Φ c→o = 4.0 10 −4
Φ o→c = 0.31
Φ c→o = 0.29
Φ o→c = 0.17
Φ c→o = 0.48
Fig. 15.1 Typical examples of diarylethenes exhibiting fluorescence (i) in the open-ring isomer,
(ii) in the closed-ring isomer, and (iii) in both open- and closed-ring isomers
Some diarylethenes exhibit fluorescence in the open-ring form and/or the closedring form. As shown in Fig. 15.1, the fluorescent diarylethenes are classified into three
types: diarylethenes exhibiting fluorescence (i) in their open-ring isomers (turn-off
mode) [2–14], (ii) in their closed-ring isomers (turn-on mode) [15–20], and (iii) in
both open- and closed-ring isomers [21–29]. Their fluorescence intensities or spectra
change upon alternating irradiation with ultraviolet (UV) and visible light because the
fluorescence properties between their open- and closed-ring forms are significantly
different. In most cases, the fluorescent diarylethenes have quite low fluorescence
quantum yield (Φ f ). It is not easy to design the fluorescent diarylethene with high Φ f
in addition to the high reactivities in photocyclization and photocycloreversion. To
overcome this point, molecular systems combining diarylethenes and fluorophores by
chemical bonding or mixing were proposed. In the systems, the fluorescence on/off
switching accompanying with the photochromic reaction was accomplished. When
diarylethene is in the open-ring form, the fluorophore exhibits fluorescence. On the
other hand, when diarylethene is converted to the closed-ring form, the fluorescence
is quenched. The processes are based on an energy transfer or intramolecular electron
S. Kobatake and T. Nakahama
S
S
Et
Et
F
F
F
F
F
F
S
S
Et
Et
F
F
F
F
F
F
Vis.
UV
O O
O O
O O
O O
S
S
Me
Me
S
S
Me
Me
F
F
F
F
F
F
Vis.
UV
S
S
Me
Me
F
F
F
F
F
F
S
S
Me
Me
F
F
F
F
F
F
Vis.
UV
F
F
F
F
F
F
(i)
(ii)
(iii)
1a
Fluorescent
(λ f = 485 nm, Φ f = 0.017)
1b
Non-fluorescent
2a
Non-fluorescent
3b
Fluorescent
(λ f = 630 nm, Φ f = 0.0001)
2b
Fluorescent
(λ f 550 nm, Φ f = 0.87)
3a
Fluorescent
(λ f = 430 nm, Φ f = 0.012)
Φ o→c = 0.42
Φ c→o = 4.0 10 −4
Φ o→c = 0.31
Φ c→o = 0.29
Φ o→c = 0.17
Φ c→o = 0.48
Fig. 15.1 Typical examples of diarylethenes exhibiting fluorescence (i) in the open-ring isomer,
(ii) in the closed-ring isomer, and (iii) in both open- and closed-ring isomers
Some diarylethenes exhibit fluorescence in the open-ring form and/or the closedring form. As shown in Fig. 15.1, the fluorescent diarylethenes are classified into three
types: diarylethenes exhibiting fluorescence (i) in their open-ring isomers (turn-off
mode) [2–14], (ii) in their closed-ring isomers (turn-on mode) [15–20], and (iii) in
both open- and closed-ring isomers [21–29]. Their fluorescence intensities or spectra
change upon alternating irradiation with ultraviolet (UV) and visible light because the
fluorescence properties between their open- and closed-ring forms are significantly
different. In most cases, the fluorescent diarylethenes have quite low fluorescence
quantum yield (Φ f ). It is not easy to design the fluorescent diarylethene with high Φ f
in addition to the high reactivities in photocyclization and photocycloreversion. To
overcome this point, molecular systems combining diarylethenes and fluorophores by
chemical bonding or mixing were proposed. In the systems, the fluorescence on/off
switching accompanying with the photochromic reaction was accomplished. When
diarylethene is in the open-ring form, the fluorophore exhibits fluorescence. On the
other hand, when diarylethene is converted to the closed-ring form, the fluorescence
is quenched. The processes are based on an energy transfer or intramolecular electron