1 Polymethine Dyes
13
1.3 Topics in Polymethine Dyes
1.3.1 Data Recording Materials
In this field, many kinds of materials such as azo complex dyes, phthalocyanines,
naphthoquinone dyes, cyanines, and oxonols have been proposed. Most important
properties for the materials are (1) the absorption band for laser light, (2) smooth
melting or sublimation upon laser irradiation, (3) good solubility in organic solvents,
and (4) good durability.
As the writing and reproducing laser wavelength for CD-R is 750–830 nm,
pentamethine dyes are most important. Pentamethine dyes can act as singlet oxygen
sensitizers to decompose themselves. Therefore, a singlet oxygen quencher must be
added to show good durability. Therefore, pentamethine dyes are used in the presence of a singlet oxygen quencher. A recording layer consisting of a pentamethine
dye 1.44 and a singlet oxygen quencher 1.45 has been proposed (Yanagisawa et al.
1993).
A material 1.46 which has a singlet oxygen quencher as a counter anion has been
reported (Namba et al. 1996).
Later, new counter anion quenchers 1.47, which show good solubility in organic
solvents, were proposed (Namba et al. 1999).
As the recording and reproducing wavelength for DVD-R is 550–620 nm, indolenine and benzindolenine trimethine dyes are suitable for this purpose. Symmetrical derivatives 1.48 and 1.49 and unsymmetrical trimethine dyes 1.50 have been
proposed as the materials.
It is known that when tetracyanonaphthoquinone (TCNQ) was added to polymethine dyes, photostability is improved. However, TCNQ is not soluble in organic
solvents. Therefore, dye 1.51, in which TCNQ is contained as a part of the counter
anion, has been proposed (Meng et al. 2001).
An oxonol dye 1.52, which does not contain heavy metals, hase been proposed.
This compound can produce gaseous CO 2 by decomposition. Bipyridyl salts effectively quench the singlet state of the oxonol dye to inhibit the singlet oxygen formation
(Mikoshiba et al. 2006). The structures of these dyes are shown in Fig. 1.8.
1.3.2 Sensitizers for DSSCs
In 2003, a merocyanine dye called “indoline dye” 1.53 (D149) was reported to act as
a highly efficient sensitizer in DSSCs (Horiuchi et al. 2003). “Indoline” means the
hydrogenated form of indole. In 2008, the octyl derivative 1.54 (D205) was reported
to show higher conversion efficiency than D149 on TiO 2 due to improved open-circuit
photovoltage (V oc ) (Ito et al. 2008)). The octyl group can prevent approaching I 3
−
species in an electrolyte. Then, the electron transfer from the semiconductor surface
to I 3
− species decreased to improve V oc . Later, an indoline dye 1.55 was reported to
13
1.3 Topics in Polymethine Dyes
1.3.1 Data Recording Materials
In this field, many kinds of materials such as azo complex dyes, phthalocyanines,
naphthoquinone dyes, cyanines, and oxonols have been proposed. Most important
properties for the materials are (1) the absorption band for laser light, (2) smooth
melting or sublimation upon laser irradiation, (3) good solubility in organic solvents,
and (4) good durability.
As the writing and reproducing laser wavelength for CD-R is 750–830 nm,
pentamethine dyes are most important. Pentamethine dyes can act as singlet oxygen
sensitizers to decompose themselves. Therefore, a singlet oxygen quencher must be
added to show good durability. Therefore, pentamethine dyes are used in the presence of a singlet oxygen quencher. A recording layer consisting of a pentamethine
dye 1.44 and a singlet oxygen quencher 1.45 has been proposed (Yanagisawa et al.
1993).
A material 1.46 which has a singlet oxygen quencher as a counter anion has been
reported (Namba et al. 1996).
Later, new counter anion quenchers 1.47, which show good solubility in organic
solvents, were proposed (Namba et al. 1999).
As the recording and reproducing wavelength for DVD-R is 550–620 nm, indolenine and benzindolenine trimethine dyes are suitable for this purpose. Symmetrical derivatives 1.48 and 1.49 and unsymmetrical trimethine dyes 1.50 have been
proposed as the materials.
It is known that when tetracyanonaphthoquinone (TCNQ) was added to polymethine dyes, photostability is improved. However, TCNQ is not soluble in organic
solvents. Therefore, dye 1.51, in which TCNQ is contained as a part of the counter
anion, has been proposed (Meng et al. 2001).
An oxonol dye 1.52, which does not contain heavy metals, hase been proposed.
This compound can produce gaseous CO 2 by decomposition. Bipyridyl salts effectively quench the singlet state of the oxonol dye to inhibit the singlet oxygen formation
(Mikoshiba et al. 2006). The structures of these dyes are shown in Fig. 1.8.
1.3.2 Sensitizers for DSSCs
In 2003, a merocyanine dye called “indoline dye” 1.53 (D149) was reported to act as
a highly efficient sensitizer in DSSCs (Horiuchi et al. 2003). “Indoline” means the
hydrogenated form of indole. In 2008, the octyl derivative 1.54 (D205) was reported
to show higher conversion efficiency than D149 on TiO 2 due to improved open-circuit
photovoltage (V oc ) (Ito et al. 2008)). The octyl group can prevent approaching I 3
−
species in an electrolyte. Then, the electron transfer from the semiconductor surface
to I 3
− species decreased to improve V oc . Later, an indoline dye 1.55 was reported to