38
T. Maeda
Fig. 2.22 Polysquaraines synthesized by Pd-catalyzed cross-coupling polymerization
Scherer et al. synthesize the oligomeric squaraine dye through the combination
of cross-coupling and condensation. The intermediate 37 bearing active methylene
terminals was synthesized by the Stille cross-coupling between brominated squaraine
dyes and indolenine derivatives with trialkyl-stannyl thiophene skeleton. Also, the
squaraine oligomer 38 with thiophene linkers was synthesized by the condensation
reaction (Fig. 2.23) (Scherer et al. 2002).
2.7 Miscellaneous Containing Squaraine Chromophores
Two-photon absorption (2PA) defined as the simultaneous absorption of two photons
of the same or different energy by a molecule enables a large variety of improved and
novel technological capabilities such as microfabrication, high-resolution fluorescence microscopy, non-destructive imaging of biological tissues, and photodynamic
therapy (He et al. 2008). The important factor to gain a large 2PA cross section is
found to be a donor-acceptor-donor conjugated system. Therefore, squaraine chromophores have a potential for 2PA dyes due to the intrinsic donor-acceptor-donor
structure. Actually, squaraine-based compounds 32 and 36 show a large 2PA cross
section. Marder et al. reported squaraine dyes bearing extended π-systems 39 and
bearing zinc porphyrin components 40 (Fig. 2.24) (Chung et al. 2006; Odom et al.
2009). Lambert et al. also demonstrated the branched squaraine chromophores for
T. Maeda
Fig. 2.22 Polysquaraines synthesized by Pd-catalyzed cross-coupling polymerization
Scherer et al. synthesize the oligomeric squaraine dye through the combination
of cross-coupling and condensation. The intermediate 37 bearing active methylene
terminals was synthesized by the Stille cross-coupling between brominated squaraine
dyes and indolenine derivatives with trialkyl-stannyl thiophene skeleton. Also, the
squaraine oligomer 38 with thiophene linkers was synthesized by the condensation
reaction (Fig. 2.23) (Scherer et al. 2002).
2.7 Miscellaneous Containing Squaraine Chromophores
Two-photon absorption (2PA) defined as the simultaneous absorption of two photons
of the same or different energy by a molecule enables a large variety of improved and
novel technological capabilities such as microfabrication, high-resolution fluorescence microscopy, non-destructive imaging of biological tissues, and photodynamic
therapy (He et al. 2008). The important factor to gain a large 2PA cross section is
found to be a donor-acceptor-donor conjugated system. Therefore, squaraine chromophores have a potential for 2PA dyes due to the intrinsic donor-acceptor-donor
structure. Actually, squaraine-based compounds 32 and 36 show a large 2PA cross
section. Marder et al. reported squaraine dyes bearing extended π-systems 39 and
bearing zinc porphyrin components 40 (Fig. 2.24) (Chung et al. 2006; Odom et al.
2009). Lambert et al. also demonstrated the branched squaraine chromophores for