139]. Interestingly, this luminescence quenching is much weaker when
Ru-ph4-TMS is bound to ZL in a dichloromethane suspension.
The explanation is that this is due to the delocalization of the emitting
3 MLCT
state over the tail of the bpy-ph4 ligand which is located inside of the channels and
thus shielded by the ZL. This hinders the O 2 in making successful collisions with the
tail [140]. An even larger shielding effect can be observed when the Ru-ph4-TMS
stopcocks are attached to a ZL monolayer. The luminescence lifetime of the attached
Ru-ph4-TMS stopcock was measured to be nearly the same under O 2 and under N 2
atmosphere under these conditions [127]. The emission spectra of the
(Ru-ph4-TMS)-ZL monolayer in N 2 and in O 2 atmosphere are shown in the lower
part of Fig. 13. The time delay between the curves shown is 200 ns. The great
similarity of both emission spectra is remarkable. The lifetime in O 2 and in N 2
atmosphere is about the same as that of the free complex in solution under N 2
atmosphere (τ ¼ 1,207 ns). This means that the ZL host provides an excellent
shielding of the emitting
3
MLCT state of Ru-ph4-TMS, preventing collisions
between the O 2 quencher and the sensitive tail of the stopcock. This also supports
the interpretation that the excited state is essentially localized on the ph4 tail
[141]. Disc-shaped crystals with an average length of 250 nm and an aspect ratio,
length to diameter, of 0.3 have been used for the preparation of the oriented monolayers used in these experiments. The oriented ZL monolayers were prepared
according to the procedure described in [111], using CP-TMS (Table 4) as covalent
linker.
De Cola et al. applied successfully micro contact printing (MCP) [142] to obtain
well-ordered and uniformly oriented ZL monolayers on conductive surfaces without
any chemical modification of the ZL or the substrate [131]. They created particular
patterns with ZL crystals that were filled with a fluorescent dye. A similar technique
was used for realizing spatial controlled channel entrances functionalization of discshaped ZL nanocrystals with two different functionalities. A stepwise procedure
allowed modifying specifically both bases of the ZL crystals: one with a suitable
chemical group, e.g., ATTO-565, and the other one with a functionalized nanoobject, e.g., magnetic iron oxide nanoparticles [135].
5.2 Chains, Files, Hexagonal, and Other Arrangements
ZL crystals have been arranged in different patterns, some of which are illustrated in
Fig. 12. The size, the aspect ratio, and the quality of the ZL particles, but also their
surface modification, are factors which determine type and quality of patterns that
can be created. The formation of files, Fig. 12d, is promoted by appropriate stopcock
modification so that the interaction between the stopcocks of two crystals
approaching each other is stronger than any other interactions [101, 143, 144]. Elongated chains can be obtained using electrospinning of a polymer, Fig. 12e [115], and
self-assembled nanofibers of fluorescent dye-ZL crystals [145]. Hexagonal patterns,
Fig. 12c, have been obtained using a surface tension-driven auto-assembly process
26
G. Calzaferri
Ru-ph4-TMS is bound to ZL in a dichloromethane suspension.
The explanation is that this is due to the delocalization of the emitting
3 MLCT
state over the tail of the bpy-ph4 ligand which is located inside of the channels and
thus shielded by the ZL. This hinders the O 2 in making successful collisions with the
tail [140]. An even larger shielding effect can be observed when the Ru-ph4-TMS
stopcocks are attached to a ZL monolayer. The luminescence lifetime of the attached
Ru-ph4-TMS stopcock was measured to be nearly the same under O 2 and under N 2
atmosphere under these conditions [127]. The emission spectra of the
(Ru-ph4-TMS)-ZL monolayer in N 2 and in O 2 atmosphere are shown in the lower
part of Fig. 13. The time delay between the curves shown is 200 ns. The great
similarity of both emission spectra is remarkable. The lifetime in O 2 and in N 2
atmosphere is about the same as that of the free complex in solution under N 2
atmosphere (τ ¼ 1,207 ns). This means that the ZL host provides an excellent
shielding of the emitting
3
MLCT state of Ru-ph4-TMS, preventing collisions
between the O 2 quencher and the sensitive tail of the stopcock. This also supports
the interpretation that the excited state is essentially localized on the ph4 tail
[141]. Disc-shaped crystals with an average length of 250 nm and an aspect ratio,
length to diameter, of 0.3 have been used for the preparation of the oriented monolayers used in these experiments. The oriented ZL monolayers were prepared
according to the procedure described in [111], using CP-TMS (Table 4) as covalent
linker.
De Cola et al. applied successfully micro contact printing (MCP) [142] to obtain
well-ordered and uniformly oriented ZL monolayers on conductive surfaces without
any chemical modification of the ZL or the substrate [131]. They created particular
patterns with ZL crystals that were filled with a fluorescent dye. A similar technique
was used for realizing spatial controlled channel entrances functionalization of discshaped ZL nanocrystals with two different functionalities. A stepwise procedure
allowed modifying specifically both bases of the ZL crystals: one with a suitable
chemical group, e.g., ATTO-565, and the other one with a functionalized nanoobject, e.g., magnetic iron oxide nanoparticles [135].
5.2 Chains, Files, Hexagonal, and Other Arrangements
ZL crystals have been arranged in different patterns, some of which are illustrated in
Fig. 12. The size, the aspect ratio, and the quality of the ZL particles, but also their
surface modification, are factors which determine type and quality of patterns that
can be created. The formation of files, Fig. 12d, is promoted by appropriate stopcock
modification so that the interaction between the stopcocks of two crystals
approaching each other is stronger than any other interactions [101, 143, 144]. Elongated chains can be obtained using electrospinning of a polymer, Fig. 12e [115], and
self-assembled nanofibers of fluorescent dye-ZL crystals [145]. Hexagonal patterns,
Fig. 12c, have been obtained using a surface tension-driven auto-assembly process
26
G. Calzaferri