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The porphyrin handbook - Kadish K.M.

Kadish K.M. The porphyrin handbook - Academic press, 2000. - 368 p.
Download (direct link): kadishsmishgulilard2000.djvu
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molecules into a large-scale
structure, which provides a wide range of freedom in the system design;
and (2) most of processes via weak noncovalent bond formation are usually
thermodynamically controlled, they are suitable for the construction of
the selfassembling systems at a relatively low temperature without
additional energy supply. Furthermore, from the practical viewpoint, it
is expected that preparation of large-scale molecular systems containing
more than ten porphyrins by using only traditional organic synthesis
based on the covalent bond will become difficult. These situations make
the self-assembling multiporphyrin systems some of the most attractive
and important challenges to porphyrin chemistry.
In the case of self-assembling systems, the porphyrin parts and the
recognition site of the system may be designed separately making
consideration of assembly-component variation possible. Some typical
assembly modes which have appeared in artificial poiphyrin assemblies are
shown in Figure 17.
Type I is a face-to-face dimerization of two porphyrins using a
stacking interaction between their wide surfaces. This type of
interaction is difficult to control artificially, though the phenomenon
had been indicated to play an important role in natural systems.214 2,6
The most basic assembly usually consists of a pair of two porphyrins
which have host and guest sites, respectively, for molecular recognition
(type II). In the case of porphyrin assemblies, one of the recognition
sites may be replaced by the poiphyrin central metal itself as shown in
type IV. Such utilization of the coordination interaction on the
porphyrin central metal sometimes greatly reduces the assemblies'
synthetic difficulties, though the mutual configuration of porphyrins is
subject to some restriction. Introduction of an
46/ Porphyrins and Metalloporphyrins as Receptor Models
329
type I
' 11
type HI'*?25^

ffA
type IV
type V
type VI
tfA
ziC~~
f
yj
<^czS
Ss. +

IPS
A , ^-
4;
\ K!\
/h
V

4>
Figure 17. Various types of self-assembling processes of multiporphyrin
systems.
independent interface molecule for molecular recognition (type III)
provides a further useful class of assemblies. The most important
advantage to this type of assembly-system extension is that one can
easily prepare a series of porphyrin assemblies having different
configurations by changing the design of the interface molecule without
modifying the porphyrin structures. Similar utilization of an interface
{
ligand is also possible for the two metalloporphyrins (type V). Type VI
is a somewhat different assembling mode, where the conformation and/or
configuration of porphyrins is regulated by association with the
interface molecule. In the practical design, these elemental assembly
modes between two porphyrins may be freely combined to construct
multiporphyrin self-assembling systems. ,<r\
As mentioned before, the coordination interaction
(, ll
provides on the central metal a convenient means available
^ , ' '
to assemble two or more porphyrin molecules. The simplest
f 4_<^"N zn
example is the coordination dimer, 170, of 5-(pyridinyl)-
--- -
octamethylporphyrin and (TPP)Zn(II) complex.217 The
Nrl! J
dimer shows interporphyrin singlet energy transfer with a
4 11
330
Ogoshi et al.
NHR,
173
173C
173a 173b
Ar
rate constant of ~1.1 x 10[o s_l. The combination of bipyridylporphyrin
with the dizinc complex of the linear porphyrin dimer gives the
corresponding trimer 171, quinone derivatives of which show both electron
and energy transfer.21X219 The similar combination of the linear
porphyrin dimer's dizinc complex with the tetrapyridyl free-base
porphyrin derivatives gives pentameric porphyrin assemblies such as 172
with the complexation constant of about 106M-'.220 The spectral behavior
of the free-base porphyrin in the pentads is determined by a nonplanar
distortion of their macrocycle caused by the two-point binding with
dimers. The structures of such self-assemblies may be regulated by
changing the angle between the plane of the porphyrin and the orientation
of the pyridine ligand. For example, the TPP derivatives, 173a, 173b, and
173c, predominantly form the cyclic dimer, trimer and tetramer,
respectively, according to their geometric orientations of the
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