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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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mesogenic materials,2'1 whereas porphyrins and metalloporphyrins have
received only cursory examination. The larger phthalocyanines tend to
have high melting points; porphyrins offer a similar geometrical
structure and a greater ease of functionalization, but have a smaller
inner
core and therefore lower, more useable melting points. The majority of
porphyrin mesogenic materials have a discotic columnar nature in which
the porphyrins stack like saucers along their short axis.
1, Octa-substituted Porphyrins
The first reported porphyrin exhibiting mesophasic behavior was an octa-
/?-substituted -porphyrin I octa-rc-dodecyl ester (Figure l)4 The
investigation was modeled on the observation that similarly shaped flat,
hexagonal molecules had previously displayed discotic liquid crystal
phases. Upon heating, the porphyrin compound melted directly from a
crystal to an isotropic liquid. During cooling, a mesomorphic phase of
0.1 C was noted between 96.8 C and 96.7 C. This phase was
characterized as having discotic order via microscopic texture analysis
and miscibility experiments in comparison to known discotic materials.
Fox and coworkers have synthesized and investigated the physical
properties of a series of octyl ether and octyl ester porphyrin
materials. The free-base and metalated derivatives of 2,3, 7, 8, 12, 13,
17, 18-octakis(/?-"-alkoxy)ethyl-porphyrin, H2((OCnH2n+i)OEP)
(abbreviations given in Table 1), were examined as possible liquid
crystalline porphyrin materials (Figure 1). Of the free-base species
examined, only the -octyl porphyrin displayed a narrow five-degree
liquid-crystalline phase (Table 2). The metalated (M = Zn, Cu, Pd, Cd)
poiphyrins demonstrated discotic mesomorphism. The lowest melting point
(61 C) was observed for an equimolar mixture of the -octyl and -decyl
zinc octaether porphyrin materials. Appendage of a single electron
donating cyano group to the 5-position of w-octyl octaether porphyrin
[FI2(OCnFbn + i)(OECNP)] resulted in depression of the melting point and
the clearing point. Substitution of an electron-accepting nitro group in
the same position [H2(OCnH2n + i)(0EN02P)] produced a depression of the
clearing point without affecting the melting transition, thereby reducing
the total range of liquid-crystalline behavior. The authors attribute
this to distortion of the planar macrocyclic ring by the large nitro
group.^ The free-base and zinc(II) derivatives of three similar octaester
porphyrins [H2((02CnH2n , i)OEP)] were found to exhibit discotic columnar
mesophases (Figure 2).
R R
R R
Figure 1, Structure of uroporphyrin I octa-n-dodecyl ester (R =
CH2C02Ci2H25, M = H2) and other octylether and octylester porphyrins (R =
, i, n = 4, 6, 8, 10 or R = CH202CnH2n ( n = 4, 6, 8; M = H2,
Zn, Cu, Pd, Cd).
41 / Porphyrin Materials Chemistry
45
Table 1. Abbreviations
(DEtyP)n 5,10,15,20-Diethylnylporphyrin polymer
(02C"H2n f i)OEP 2,3,7,8,12,13,17,18-octakis (/?--
1181)11111
(OCnH2n4 i)DPP 5,15-bis(4-n-alkoxyphenyl)porphyrinate
(OCnH,n + ,)OECNP 2,3,7,8,12,13,17,18-octakis(/:f-n-aIkoxy)ethyI-5-
cyanoporphyrinate
(OC"H,n t ,)OENCbP 2,3,7,8,12,13,17,18-octakis(/i-n-alkoxy)ethyl-5-
nitroporphyrinate
(OCnH2n , ,)OEP 2,3,7,8,12,13,17,18-octakis(/i-n-
aLkoxy)ethylporphyrinate
[(C"H2" + ,)Cy]2DPP 5,15-bis(4'-n-aIkylcyclohexyl-4-
esterphenyl)porphyrinate
(CnH2n M)Cy)OHPP 5-(4'-"-alkyIcycloliexyl-4-esterphenyl)-15-(4-
hydroxyphenyl)porphyrinate
[(OCnH."+lbPh],DPP 5,15-bis(2',4'-n-alkoxyphenyl-4-
esterphenyl)porphyrinate
[(OCnH2n t i)3Ph]2DPP 5,15-bis(2',4',6'-n-aIkoxyphenyl-4-
esterphenyl)porphyrinate
[(OC"H2n Hl)Ph]2DPP 5,15-bis(4'-n-alkoxyphenyI-4-
esterphenyl)porphyrinate
[(OC"H2n+l)Ph]OHPP 5-(4'-1-11-4-81111)-15-(4-
11)111
APTES 3-aminopropyltriethoxysilane
B(C"H2n H0)mTP 5,15-5(3,4,3",4"-1-1-"-
11)111
BDPY boron-dipyrrin
Bpy Bipyridine
Br"TPP 2,3,7,8,12,13,17,18-octabromo-5,10,15,20-
111!
D-(DPP)-A 5-[(4'-11)-1)1]-15[(4"-
1)1]-,20^1}111
D-A donor-acceptor pair
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