separate components. This allows the generation of novel materials with individual
nano-characteristics that can be translated into macroscopic properties. Some early
examples of such self-assembly patterns are reported in Fig. 12.
5.1 Oriented Monolayers
The arrangements that attracted most interest are dense monolayers of ZL crystals
with the c-axis oriented perpendicularly with respect to the surface. The preparation
of dense monolayers of zeolite crystals in the nanometer to micrometer size regime
was originally motivated by the desire to designing chemical structures on electrode
surfaces that redefine the chemical and physical microenvironment in which heterogeneous electron transfer reactions occur [118–122]. The first high-quality dense
monolayer was achieved with crystals of zeolite A of rather perfect cubic morphology [123]. Strongly luminescent silver sulfide quantum dots were prepared in the
first ship-in-a-bottle synthesis on such a zeolite A monolayer [124]. The preparation
of oriented ZL monolayers presented an additional challenge with respect to the
cubic zeolite A layers. The first successful preparation of such oriented ZL monolayers illustrated in Fig. 12b was reported simultaneously by G. Calzaferri et al. and
by K. B. Yoon et al. in the same issue of Angewandte [111, 112]. This initiated much
interest because this pattern can be used in optical and electro-optical experiments,
for selective gas separation membranes, chemical sensors, micro contact transfer
printing, as well as studying cell adhesion or neuron properties, both of biological
and biomedical interest. Different ways for obtaining such monolayers have been
explored. Disc-shaped crystals are easier to handle than elongated ones. The
narrower the size distribution and the more perfect the morphology of the crystals,
the higher the quality of the monolayers. The general principles for monolayer
preparation reported in refs. [111, 123, 125] remain valid. Li et al. reported an
interesting method for obtaining highly luminescent and transparent ZL monolayers
[126]. A variety of preparation techniques, including utilization of strong magnetic
fields or optical tweezer forces, have been investigated in order to meet special needs
[73, 76, 109, 123–136]. Subsequent insertion of guests into the channels and
addition of stopcocks are, however, only possible if the free channel openings are
not blocked or damaged during the preparation of the monolayer [111]. A special
example concerns the suppression of luminescence quenching of a ruthenium
complex by oxygen. The Ru
2+ complex (Ru-ph4-TMS, Table 4) has a tail which
nicely fits into the channels of ZL. The head is positively charged and can therefore
bind electrostatically to the negatively charged channel entrance, as illustrated in
Fig. 13. The van der Waals model indicates that the size of the head is such that it
plugs the channels quantitatively and the center to center distance of 18.4 Å between
two channel entrances ensures that there is enough space for the heads of adjacent
Ru-ph 4-TMS stopcocks. It is well known that the luminescence of such Ru
complexes is quenched by O 2 via a diffusion-controlled collision [137–
24
G. Calzaferri
nano-characteristics that can be translated into macroscopic properties. Some early
examples of such self-assembly patterns are reported in Fig. 12.
5.1 Oriented Monolayers
The arrangements that attracted most interest are dense monolayers of ZL crystals
with the c-axis oriented perpendicularly with respect to the surface. The preparation
of dense monolayers of zeolite crystals in the nanometer to micrometer size regime
was originally motivated by the desire to designing chemical structures on electrode
surfaces that redefine the chemical and physical microenvironment in which heterogeneous electron transfer reactions occur [118–122]. The first high-quality dense
monolayer was achieved with crystals of zeolite A of rather perfect cubic morphology [123]. Strongly luminescent silver sulfide quantum dots were prepared in the
first ship-in-a-bottle synthesis on such a zeolite A monolayer [124]. The preparation
of oriented ZL monolayers presented an additional challenge with respect to the
cubic zeolite A layers. The first successful preparation of such oriented ZL monolayers illustrated in Fig. 12b was reported simultaneously by G. Calzaferri et al. and
by K. B. Yoon et al. in the same issue of Angewandte [111, 112]. This initiated much
interest because this pattern can be used in optical and electro-optical experiments,
for selective gas separation membranes, chemical sensors, micro contact transfer
printing, as well as studying cell adhesion or neuron properties, both of biological
and biomedical interest. Different ways for obtaining such monolayers have been
explored. Disc-shaped crystals are easier to handle than elongated ones. The
narrower the size distribution and the more perfect the morphology of the crystals,
the higher the quality of the monolayers. The general principles for monolayer
preparation reported in refs. [111, 123, 125] remain valid. Li et al. reported an
interesting method for obtaining highly luminescent and transparent ZL monolayers
[126]. A variety of preparation techniques, including utilization of strong magnetic
fields or optical tweezer forces, have been investigated in order to meet special needs
[73, 76, 109, 123–136]. Subsequent insertion of guests into the channels and
addition of stopcocks are, however, only possible if the free channel openings are
not blocked or damaged during the preparation of the monolayer [111]. A special
example concerns the suppression of luminescence quenching of a ruthenium
complex by oxygen. The Ru
2+ complex (Ru-ph4-TMS, Table 4) has a tail which
nicely fits into the channels of ZL. The head is positively charged and can therefore
bind electrostatically to the negatively charged channel entrance, as illustrated in
Fig. 13. The van der Waals model indicates that the size of the head is such that it
plugs the channels quantitatively and the center to center distance of 18.4 Å between
two channel entrances ensures that there is enough space for the heads of adjacent
Ru-ph 4-TMS stopcocks. It is well known that the luminescence of such Ru
complexes is quenched by O 2 via a diffusion-controlled collision [137–
24
G. Calzaferri