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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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transitions were observed at 31.0, 52.0 and 155.0 C. This material was
determined to be a discotic lamellar (DL) liquid crystal via X-ray
diffraction studies.15 Novel ferromagnetic materials were prepared by
mixing two different paramagnetic M[T(4-rc-C|2FI25)PP] materials [M =
Cu(II), V(IV), Co(II), Mo(V), Ag(II) or Fe(II)].16
The mesogenic behavior of 5,10,15,20-tetrakis(4-rc-
alkyloxyphenol)porphyrins, [2((/?-- |0H2| )PP] and H2[T(p-n-
OCI2H25)PP)], was explored by Kugimiya and Takemura. Two liquid-
crystalline phases were attributed to each the free-base and cobalt(II)
derivatives of T(p-n-)21). A large temperature regime for
mesomorphism was found for Con[T(p-n-OCI(,H2|)PP]. The zinc(II) complex
featured three liquid-crystal phases between - 16 and 170 C. The first
two phases were not observed during repeated melting cycles of the
material.17
Ohta and coworkers presented a number of porphyrins synthesized
specifically in order to examine their liquid-
Figure 2. Schematic representation of the tilted columnar stacking.7
Figure 3. Schematic representation of the columnar arrangement of
discotic zinc -decyl ether octa-substituted porphyrin stacks. Reprinted
with permission from Liu, C. Y.; Pan, H. L.; Tang, H.; Fox, M. A.; Bard,
A. j. ]. Phys. Chem. 1995, 99, 7632 (c) 1995 American Chemical Society.
crystalline characteristics. The highly substituted
5,10,15,20-tetrakis(3,4,3",4"-tetradodecyloxy-6>-terphenyl)-porphyrins
{[H2[T(CI2H250)i6TP]}, although possessing core tetra-substituted
porphyrin rings, have sixteen long alkyl chains for inducing mesogenic
behavior (Figure 9). The di-substituted dodecyl ether porphyrin, H2[(T-
(C|2H250)I6TP], displayed an extremely complicated DSC trace-at least
four different mesophases were noted. By X-ray diffraction, a discotic
hexagonal-ordered columnar material (Dho) was identified which melted at
- 80 C
48
Chou et al.
Figure 4. Readout current pulses with the same writing conditions: (a)
initial readout and (b) after 1.5 billion write/erase cycles. Reprinted
with permission from, Liu, C.-Y.; Pan, H. L.; Fox, M. A.; Bard, A. J.
Chem. Mater. 1997, 9, 1422. (c) 1997 American Chemical Society.
R=C,H 17
Figure 5. Structure of sulfur-substituted azaporphyrin.
2(2)| Figure 6. Structure of -
pentadecylphenyl porphyrin.
and cleared at 39 C. A second mesophase that cleared at 59 C was
determined to be discotic hexagonal-disordered columnar (Dhd). Upon
cooling, two other unidentified phases were observed. The similar di-
substituted dodecyl
TEMPERATURE
140 120 eo 60 40
Figure 7. Temperature dependence of the dark-current under 4000 V/cm.
Reprinted with permission from Shimizu, Y.; Ishikawa, A.; Kusabayashi, S.
Chem. Lett. 1986, 1041.
TEMPERATURE/*C
140 120 100 80 60 40
Figure 8. Temperature dependence of the photocurrent at
620 nm under 4000 V/cm. Reprinted with permission from Shimizu,
Y.; Ishikawa, A.; Kusabayashi, S. Chem. Lett. 1986, 1041.
ether copper complex, ((|2250)|), exhibited one Dhd mesophase
that melted at - 37 C and cleared at 57 C. The authors credit steric
influences of the sixteen long alkoxyl chains to the formation of a
columnar assembly (versus lamellar which was observed for by Shimizu.15).
When one of the alkoxyl groups on each of the eight pendant phenyl groups
was replaced with a proton, H2[T(Cl2H250)8TP], a high-melting (202.2 C),
nonliquid crystalline material resulted.18 Di-substituted o-terphenyl
mesogenic porphyrins materials were also studied and are reviewed here.
41 / Porphyrin Materials Chemistry
49
Figure 9. Structure of substituted 5,10,15,20-tetrakis(3,4,3",4"-
tetradecyloxy-o-terphenyl)porphyrins (R1 - R2 - n-C, 2H250;
M = H2 or Cu; or R1 = n-C,2H250, R2 = H; M = H2).
Controlled orientation of the porphyrin macrocycle in a liquid
solution for use in electron paramagnetic resonance (EPR) experiments was
the motivation for the synthesis of an orf/io-amino-tetraphenylporphyrin
based liquid crystalline material. Appending biphenyl long chain alkoxyl
groups to the ortho-amino substituents generated a meso-genic material in
which the porphyrin macrocyclic plane was orthogonal relative to the
director L in a nematic phase matrix. Unaltered tetraphenylporphyrin
aligns such that the macrocyclic ring is parallel to L (Figure 10).19 20
Griesar et al. synthesized a material that had both liquid crystal and
ferrimagnetic properties. A discotic mesophase was observed between 108
and 155 C for Mnm [T(p-n-OC12H25)PP](TCNE)-2 toluene (TCNE =
tetracyanoethy-lene). The X-ray diffraction pattern revealed that the
material possessed a hexagonal columnar lattice with a characteristic
intercolumnar spacing of 30 A. The system was also found to display
ferrimagnetic behavior below 25.0 K.21
Liquid-crystalline behavior can also be induced in some hydroxy-
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