316
K. Tanaka et al.
From simply mixing in the solution and casting on the substrate, the homogeneous hybrid film was obtained from PUPOSS and 0.5 wt% PF. The 0.5 wt%
loading ratio was enough to observe luminescence from the product. When the pristine polyurethane was used, phase separation occurred in 0.5 wt% PF loading ratio,
indicating that the POSS contributes to improve compatibility with polyurethane.
The hybrid film from PUPOSS and 0.5 wt% PF had good elasticity which was
almost the same with the pristine polyurethane. Moreover, it is disclosed that the
hybrid film enhanced the mechanical property and absolute emission efficiencies.
This means that both components should be mixed at the nano level and the aggregates of PF are partially suppressed by POSS. It is known that PF shows not only
blue emission from a locally excited state (LE) but also yellow-greenish emission
from an excimer state in the solid and the film state (Scott et al. 1999). Since the
excimer emission was not observed in the solution state, the yellow-greenish emission from our materials should be originated from intermolecular or intramolecular interaction of the PF chains. Hence, it was presumed that elongation of the
elastic hybrid film released micro-order aggregates and subsequently induced emission color change. Indeed, after elongation of the hybrid film, the emission color
was altered from yellow green to white green and it was observable by the naked
eye (Fig. 9.4b). From the PL spectra, it was shown that the blue emission from the
LE state increased and the yellow-greenish emission in the excimer state decrease
after stretching. The phenomenon is called mechanochromic luminescence and is a
key character for constructing mechanical force sensors. These results represent that
different functions of the polymers are successfully hybridized by utilizing POSS
as a mediator. In this section, it is proved that the unique properties of POSS can
combine the distinctly different polymer functions, such as luminescent properties
and stimuli-responsiveness, and offer novel polymer materials.
9.3 Steric Effect
Another strategy for avoiding ACQ in the condensed state is the modification with
the steric groups around chromophores. As a representative example, POSS has
been used for this purpose. The modified polyphenylene ethynylenes, which often
show critical ACQ in film similarly to other conventional conjugated polymers
due to long main-chain conjugation, were synthesized with the POSS side chains
(Fig. 9.5) (Miyake and Chujo 2008). From the evaluation of emission efficiencies, significant emission was detected in film. In addition, emission color was
able to be altered by changing the introduction ratio of POSS. The degree of
inter-chain interaction might be dominant for emission color variation.
In the dye molecules, the steric substituents can play an effective role in
suppression of ACQ by disturbing intermolecular interaction. Boron complexes with
π-conjugated ligands are known to be a promising platform for designing a luminescent dye because of rigid and planar structures because structural relaxation in the
excited state can be effectively suppressed by the boron complexation (Tanaka and
K. Tanaka et al.
From simply mixing in the solution and casting on the substrate, the homogeneous hybrid film was obtained from PUPOSS and 0.5 wt% PF. The 0.5 wt%
loading ratio was enough to observe luminescence from the product. When the pristine polyurethane was used, phase separation occurred in 0.5 wt% PF loading ratio,
indicating that the POSS contributes to improve compatibility with polyurethane.
The hybrid film from PUPOSS and 0.5 wt% PF had good elasticity which was
almost the same with the pristine polyurethane. Moreover, it is disclosed that the
hybrid film enhanced the mechanical property and absolute emission efficiencies.
This means that both components should be mixed at the nano level and the aggregates of PF are partially suppressed by POSS. It is known that PF shows not only
blue emission from a locally excited state (LE) but also yellow-greenish emission
from an excimer state in the solid and the film state (Scott et al. 1999). Since the
excimer emission was not observed in the solution state, the yellow-greenish emission from our materials should be originated from intermolecular or intramolecular interaction of the PF chains. Hence, it was presumed that elongation of the
elastic hybrid film released micro-order aggregates and subsequently induced emission color change. Indeed, after elongation of the hybrid film, the emission color
was altered from yellow green to white green and it was observable by the naked
eye (Fig. 9.4b). From the PL spectra, it was shown that the blue emission from the
LE state increased and the yellow-greenish emission in the excimer state decrease
after stretching. The phenomenon is called mechanochromic luminescence and is a
key character for constructing mechanical force sensors. These results represent that
different functions of the polymers are successfully hybridized by utilizing POSS
as a mediator. In this section, it is proved that the unique properties of POSS can
combine the distinctly different polymer functions, such as luminescent properties
and stimuli-responsiveness, and offer novel polymer materials.
9.3 Steric Effect
Another strategy for avoiding ACQ in the condensed state is the modification with
the steric groups around chromophores. As a representative example, POSS has
been used for this purpose. The modified polyphenylene ethynylenes, which often
show critical ACQ in film similarly to other conventional conjugated polymers
due to long main-chain conjugation, were synthesized with the POSS side chains
(Fig. 9.5) (Miyake and Chujo 2008). From the evaluation of emission efficiencies, significant emission was detected in film. In addition, emission color was
able to be altered by changing the introduction ratio of POSS. The degree of
inter-chain interaction might be dominant for emission color variation.
In the dye molecules, the steric substituents can play an effective role in
suppression of ACQ by disturbing intermolecular interaction. Boron complexes with
π-conjugated ligands are known to be a promising platform for designing a luminescent dye because of rigid and planar structures because structural relaxation in the
excited state can be effectively suppressed by the boron complexation (Tanaka and