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Ogoshi et al.
N N' ß 'N^N
//n h' h n"V 'N
= H H = ij
Figure 19. Hexaporphyrin assembly having triaminotriazine-barbituric
hydrogen bond interface.
' r" H \ ~'1 '
Ô j. \ : Ô
' ÷ H J-: Pr' ' q -
'(fni hn ' ^N0
CH30-(CH2)604 >-0-(ÑÍ2)á-0^4 )-Î-(ÑÍã)á-0^. ^0-<ÑÍ2)á-ÎÑÍ3
0 0 0 0 0 0
Figure 20. The hydrogen bond system of the trench porphyrin-tartrate
complex and the array assembled on the tartrate template.
Artificial hydrogen-bonding systems built on porphyrin molecules are
also utilized for the construction of the multiporphyrin self-assembly.
The double-bridged tetraphenylporphyrin derivative specifically
recognizes dialkyl L-tartrates through four simultaneous hydrogen
bonds.235 Because preparation of the molecule containing multitartrate
binding sites is much easier than that of multiporphyrin systems itself,
it is an interesting possibility to construct the porphyrin assemblies by
using the oligomeric tartrates as the templates. The trench porphyrin
bridged with the 2,4-dinitro-isophthaIoyl moiety is actually found to
form the self-organized porphyrin array 189 on the tritartrate template
at low temperature.236 Upon assembly formation, the porphyrin components
show a clearly split Soret band due to the exciton-coupling interaction
between the adjacent porphyrins which resembles that observed for
linked porphyrin arrays.149-203 The thermodynamic analyses for 189
indicate that the binding constants for all stepwise association
processes (about I Î6 M 1) are rather insensitive to occupancies of the
adjacent binding sites. Combination of the hydrogen bond for the tartrate
ester and the coordination interaction gives another type of the
multiporphyrin assembly 190.237 The assembly formation is independent of
the mixing sequences of the three components, the double-bridged
porphyrin, the octaethyl-porphyrin Rh complex and the tartrate template
having two pyridine moieties.
As suggested in the case of the assembly 187, the selfassembling
processes occasionally induce a conformational change in the assembling
components. Such phenomena are observed more evidently for the assembling
processes of m&so-tetrakis(2-carboxy-4-nonylphenyl)porphyrin to form
46/Porphyrins and Metalloporphyrins as Receptor Models
°'H H' 0 >
ty/H = Ã N
Figure 21. The quaternary self-assembling system composed of two kinds of
porphyrins and the tartrate linker.
Figure 22. Formation of dimeric assembly and atropisomerization of meso-
its dimer 191 through hydrogen-bonding interactions between carboxy
groups.2'1-2 ,x This porphyrin shows strongly solvent-dependent
atropisomerization and performs self-induced conformational change to
give the porphyrin dimer 191 in nonpolar solvents. The association
constant for the dimer of the ccaaa-atropisomer is so large (>107M ') in
toluene that the atropisomerization equilibrium completely shifts to 191
even when the assembling reaction starts from the statistical mixture of
all isomers. The dimer further binds pyrazine derivatives into its inner
space with association constants of 107M 1 order.24 The most
characteristic feature of this system is that the pyrazine derivative,
bearing a large side-chain moiety such as the benzoyl group, can
coordinate two zinc atoms inside the dimer cavity by projecting the side-
chain moiety out of a window formed between hydrogen-bond pillars of the
The interaction between the crown ether and ammonium cation is also
found to be useful for construction of a porphyrin assembly. The
Ogoshi et al.
Figure 23. Interwoven cofacial porphyrin dimer.
Cu complex assembles with four molecules of the ditopic crown ether to
generate a unique six-component interwoven complex 193 where the four
crown ether macrorings would tie two porphyrin subunits together in a