Chemistry Reference
In-Depth Information
Ph
x
y
Ph
Ph
Ph
Ph
Ph
O
O
Ph
NC
C
N
Ph
O
NC
Ph
CN
15
Ph
16
C
Ph
Ph
O
O
O
S
O
O
17
O
n
18
Fig. 7 Chemical structures of polyfullerenes with NLO properties
polymers in electroluminescent devices [
77
,
94
,
95
] and in non-volatile flash
devices [
96
], among others. One of the most promising applications for
polyfullerenes seems to be as an active layer in optical limiters. These are devices
that strongly attenuate optical beams at high intensities while exhibiting higher
transmittance at low intensities, which are used for protecting human eyes and
optical sensors from intense laser beams. In this regard, C
60
is an excellent optical
limiter operating in a reverse saturable absorption mode [
97
], and its derivatives
may be considered as potent broadband optical limiters due to the broad coverage of
the characteristic ground- and excited-state absorptions over a wide wavelength
range [
98
,
99
]. However, the poor solubility and processibility of fullerene has
limited its use in optical limiting devices and for this reason, in order to overcome
such a drawback, C
60
has been incorporated in polymeric matrices. In Fig.
7
some
examples of fullerene-containing polymers used for optical limiting are collected.
In 1995 random solid fullerene-containing polystyrenes (PS) showed nonlinear
optical (NLO) properties about five times greater than those of a C
60
solution
[
100
,
101
]. Later on, random poly(methyl methacrylate) [
102
] and linear PS-
containing fullerene 15 (Fig.
7
)[
103
] were found to be optical limiters. In 2000
the star shaped C
60
containing poly(1-phenyl-1-butyne) 16 turned out to be stable,
and film-forming with a fullerene content of up to 9.1 wt%. NLO studies revealed
that at 532 nm (Nd:YAG laser) 16 shows improved optical limiting performances
compared to C
60
in solution at a linear transmission of 43% [
104
]. In the same year
the side chain polyfullerene 17, prepared by Friedel-Crafts addition of C
60
and of a
C
60
-derivative to a polycarbonate, also displayed good optical limiting properties
