Discotic liquid crystals of transition metal complexes 58 : Novel phthalocyanine-based mesogenic monomers and polymers exhibiting spontaneous homeotropic alignment and helical tetragonal columnar structure

Two synthetizations of a novel series of phthalocyanine-based discotic liquid crystals substituted by a polymerizable group, acryloyl group or a norbornene group: 2-(12-acryloyloxydodecyloxy)-3-methoxy-9,10,16,17,23,24-hexakis (3,4-dialkoxyphenoxy)phthalocyaninato copper(II) [abbreviated as (n,12)PcCu(OCH[Formula: see text])(Acryloyl) (7: e ([Formula: see text] = 10), f ([Formula: see text] = 12), g ([Formula: see text] = 14))] and 2-(12-norborn-2-ene carbonyloxydodecyloxy)-3-methoxy-9,10,16,17,23,24-hexakis(3,4-dialkoxyphenoxy)-phthalocyaninato copper(II): [abbreviated as (n, 12)PcCu(OCH[Formula: see text])(Norb) (9e, f, g)]. Their liquid crystalline properties and homeotropic alignment were investigated using a polarizing microscope, a differential scanning calorimetry (DSC), and a temperature-variable X-ray diffractometer. As a result, each of the derivatives gave a Col[Formula: see text] mesophase in the higher temperature region, displaying perfect homeotropic alignment between the two glass plates. In order to obtain the thin film while keeping their homeotropic alignment at room temperature, attempts to polymerize the monomers, 7 and 9, in the Col[Formula: see text] phase showed homeotropic alignment. The polymerization of the acryloyl-substituted monomers (7) was not successful in any of the methods, whereas the polymerization of norbornene-substituted monomers (9) was quite successful by ring-opening metathesis polymerization with a Grubbs catalyst to obtain the novel polymers, poly-(n, 12)PcCu(OCH[Formula: see text])(Norb) (10e, f, g). Each of the polymers (10) were found to show a perfect homeotropic alignment from room temperature to ca. 200[Formula: see text]C of the decomposition temperature. Moreover, it was also revealed from temperature-variable small-angle X-ray diffraction studies that each of the polymers 10 showed a helical Col[Formula: see text] (helical tetragonal columnar) structure. The helical Col[Formula: see text] phase structure may be able for use in organic electroluminescent devices and solar cells in the future.

Discotic liquid crystals of transition metal complexes 57: X-ray diffraction halo jumps originated from sudden free rotation of substituent groups to induce mesomorphism

We have synthesized a novel series of four flying-seed-like liquid crystals (1Ph-PhO)4PcM [5-M: M = Co (5-Co), Ni (5-Ni), Cu (5-Cu) and Zn (5-Zn)] which are based on a phthalocyanine core having peripheral bulky groups without long alkyl chains, in order to clarify the precise mechanism inducing their mesomorphism. For comparison, we have also synthesized a long alkyl-chain-substituted liquid crystal ([Formula: see text]C[Formula: see text]OPhO)8PcCu (7o) having the same phthalocyanine core with long alkyl chains in the periphery. Each of the derivatives 5-M and 7o showed a hexagonal ordered columnar (Colho) mesophase. Very interestingly, the halo positions in the X-ray diffraction patterns for the Colho mesophases of the flying-seed-like liquid crystals 5-M and the long alkyl-chain-substituted liquid crystal 7o were quite differently given at 5.7–6.2 Å and 4.6–4.7 Å, respectively. The halo positions of the representative derivatives 5-Cu and 7o having the same copper phthalocyanine (PcCu) core were finely measured at various temperatures by using the temperature-variable small angle X-ray diffraction technique. As the result, the derivatives 5-Cu and 7o showed sudden jumps of halo position from 5.5 to 5.7 Å and from 4.2 to 4.6 Å, respectively, at the phase transition from the crystalline phase to the liquid crystalline phase (Colho). This means that the volume changes ([Formula: see text]V) corresponding to these halo jumps originate from two different kinds of mechanisms by sudden free rotation of the bulky substituents and by sudden melting of the long alkyl chains. Thus, in this work we have unambiguously clarified these two different mechanisms inducing mesomorphism.

Discotic liquid crystals of transition metal complexes 56: Synthesis of mesogenic phthalocyanine-fullerene dyads and influence of the substitution position of alkoxy chains and the kind of terminal groups on appearance of the helical supramolecular structure

We have synthesized twelve novel discotic columnar liquid crystals based on a phenoxy-group-substituted phthalocyaninato copper(II) complex having the same alkoxy chain of C[Formula: see text]H[Formula: see text]O at different positions in the phenoxy group: the parent compounds {0a~0c-16}and the OH-substituted compounds {3a~3c-16}, the OFBA-substituted compounds {2a~2c-16}and the C[Formula: see text]-substituted dyads {1a~1c-16}. The letters of a, b and c mean substitution positions of C[Formula: see text]H[Formula: see text]O group at [Formula: see text], [Formula: see text] and [Formula: see text], respectively. We have investigated the influence of both substitution position of the alkoxy chains and the kind of terminal groups (OH, OFBA and C[Formula: see text] on the mesomorphism and the helical supramolecular structure, by using DSC, POM and temperature-variable small angle X-ray diffraction measurements. As a result, an additional big peak (Peak H) tends to appear at around 2[Formula: see text] = 1.1[Formula: see text] in the X-ray diffraction patterns only for the dyads {1a~1c-16}but not for the other compounds, {0a~0c-16}, {3a~3c-16}and {2a~2c-16}, regardless of the substitution positions of the alkoxy group. Moreover, we revealed that both the m-substituted derivative 1a-16 and the m,p-substituted derivative 1c-16 gave Peak H, but that only the p-substituted derivative 1b-16 did not give Peak H among these three dyads {1a~1c-16}. From the temperature-variable small angle X-ray diffraction measurements for the m,p-substituted derivative 1c-16 using two different sample preparation methods, we proved that the Peak H originates from a helical pitch of fullerenes. We also pointed out that the m-substituted long alkoxy chains are at least needed to form the helical supramolecular structure in the present (PhO)[Formula: see text]PcM-C[Formula: see text]-based dyads.

Discotic liquid crystals of transition metal complexes 52: Synthesis and homeotropic alignment of liquid crystalline phthalocyanine-fullerene dyad bridged by vanillin

We have synthesized a novel liquid crystalline phthalocyanine(Pc)-fullerene(C[Formula: see text] dyad (C[Formula: see text]S)[Formula: see text]PcCu-VAN-C[Formula: see text] (3a) bridged by an inexpensive natural product of vanillin (VAN), instead of the previous long [Formula: see text]-alkylene chain spacer. We have also synthesized a comparative dyad (C[Formula: see text]S)[Formula: see text]PcCu-OPh-C[Formula: see text] (3b) bridged by [Formula: see text]-hydroxybenzaldehyde (OPh), in order to investigate the influence of the methoxy group in the vanillin moiety on homeotropic alignment between two glass plates. Very interestingly, homeotropic alignment could be observed only for the dyad (C[Formula: see text]S)[Formula: see text]PcCu-VAN-C[Formula: see text] (3a) having a methoxy group in the vanillin moiety, whereas it could not be observed for the dyad (C[Formula: see text]S)[Formula: see text]PcCu-OPh-C[Formula: see text] (3b) having no methoxy group at the phenoxy group. It is very noteworthy that such a slight difference in these molecular structures between 3a and 3b becomes a crucial point to show the homeotropic alignment. Each of the dyads, 3a and 3b, showed two hexagonal ordered columnar (Col[Formula: see text] mesophases. Each of the Col[Formula: see text] mesophases in 3a and 3b gave an additional very strong reflection peak named as Peak H in a very low angle region of the SAXS (small angle X-ray scattering) pattern. Peak H could be established, from two different SAXS measurement methods, as one pitch in a helical structure of the fullerenes around the Pc column.

Photoinduced Electron Transfer in a Zinc Phthalocyanine-Fullerene Conjugate Connected by a Long Flexible Spacer

A hexadodecyl-substituted zinc phthalocyanine covalently linked through a flexible spacer to a fullerene-ZnPc-C₆₀ -has been investigated regarding electron transfer from the photoexcited, electron-donating ZnPc to the electron-accepting C₆₀ . While ground-state interactions between electron donor and acceptor within ZnPc-C₆₀ could not be detected via steady-state absorption spectroscopy, clear proof for excited-state interactions came from steady-state fluorescence spectroscopy. To this end, the fluorescence in ZnPc-C₆₀ is strongly quenched with quantum yields in THF as low as 0.05. Insight into excited-state electron-transfer deactivation within ZnPc-C₆₀ came from time-resolved femtosecond transient absorption spectroscopy. For example, upon exclusive excitation of the phthalocyanine within the ZnPc-C₆₀ conjugate, a set of transients evolve featuring, on the one hand, the signature of the one-electron oxidized ZnPc radical cation and, on the other hand, of the one-electron reduced C₆₀ radical anion. The analysis of the corresponding dynamics in chlorobenzene resulted in lifetimes for charge-separation and charge-recombination of 7.4 ps and 2.2 ns, respectively.

Flying-seed-like liquid crystals 5: Liquid crystals based on octakisphenylthiophthalocyanine and their optical properties

We have synthesized three novel flying-seed-like liquid crystals based on phthalocyaninato copper(II) (abbreviated as PcCu ) substituted by bulky groups {(o- C1) PhS (i), (m- C1) PhS (j), [m, p-( C1)2] PhS (k)} instead of using long alkyl chains, in order to investigate their mesomorphism. Their phase transition behavior and the mesophase structures have been established by using a polarizing optical microscope, a differential scanning calorimeter, and a temperature-dependent small angle X-ray diffractometer. As the results, [(o-C1)PhS]8PcCu (8i), [(m-C1)PhS]8PcCu (8j) and {[m,p-(C1)2]PhS}8PcCu (8k) show a Coltet.omesophase at 314.9~362.9 °C, a Colro(P2m) mesophase at 287.4~334.2°C and a Colro(P2m) mesophase at 331.8~386.8°C, respectively. Very interestingly, each of the derivatives thus exhibits a columnar mesophase at very high temperatures. The mesomorphism is apparently originated from the novel bulky groups (i~k). It is also noteworthy that the Q-bands of the present PhS-containing Pc derivatives 8i~8k in THF significantly red-shift by about 35 nm in comparison with those of the corresponding PhO-containing derivatives in THF.

Flying-seed-like liquid crystals. Part 4: a novel series of bulky substituents inducing mesomorphism instead of using long alkyl chains

We have synthesized a novel series of flying-seed-like liquid crystals substituted by bulky groups instead of using long alkyl chains. The derivatives having methoxy group(s) at the meta position(s) of a phenoxy group tend to show mesophase(s).

Systematic investigation of phthalocyanines, naphthalocyanines, and their aza-analogues. Effect of the isosteric aza-replacement in the core

A series of zinc complexes of phthalocyanines, naphthalocyanines and their aza-analogs was studied and compared using UV-vis and MCD spectra, molecular calculations, and photophysical and electrochemical measurements.

Discotic liquid crystals of transition metal complexes 51: Synthesis and mesomorphism of flat-pumpkin-shaped phthalocyanine-fullerene dyads

We have synthesized a novel type of donor–acceptor liquid crystalline material, phthalocyanine-fullerene ( Pc - C 60) dyad, [m,p,m′-( C 14 O )3 PhO ]6 PcCu - C 60 (7), and the Pc precursors, [m,p,m′-( C 14 O )3 PhO ]6 PcCu - OFBA (6) and [m,p,m′-( C 14 O )3 PhO ]6 PcCu - OH (5), and established their mesomorphism by using a polarizing optical microscope, a differential scanning calorimeter and a small angle X-ray diffractometer. Very interestingly, their corresponding previous parent Pc derivative, [m,p,m′-( C 14 O )3 PhO ]8 PcCu (4), shows a very wide temperature region ca. 90°C of a bicontinuous Cub(Pn3m) mesophase, whereas the present children Pc precursors (5 and 6) and Pc- C 60 dyad 7 show not the Cub mesophase but a Colho mesophase. It is also noteworthy that the staking distance in the Colho mesophase of the Pc- C 60 dyad 7was a very big value of ca. 9.1 Å, which is the biggest in discotic liquid crystals to our best knowledge. It may be originated from the biggest excluded volume caused by thermal fluctuation of peripheral long alkoxy chains at m, m′-positions. The excluded volume caused by thermal fluctuation of the peripheral long chains is so big that the molecular shape of the Pc derivative 4 and the Pc- C 60 dyad 7 very resembles a flat pumpkin.

Discotic liquid crystals of transition metal complexes 50: spiranthes-like supramolecular structure of phthalocyanine-fullerene dyads

We have synthesized novel liquid crystalline Pc - C 60 dyads (CnS)6PcCu-C60 (n = 14, 16, 18: 1a–1c) by using our developed synthetic method in order to investigate the mesomorphism and alignment behavior. Each of the (CnS)6PcCu-C60 dyads shows perfect homeotropic alignment in the Colho mesophase between two glass plates for n = 14, 16, 18 and also on a glass plate for n = 14, although none of the parent Pc compounds (CnS)8PcCu and the Pc precursors (CnS)6PcCu-OH and (CnS)6PcCu-OFBA shows homeotropic alignment. It may be attributed to the strong affinity between fullerene and glass surface. Although the reason is not so clear at the present time, this is very useful guideline for the molecular design to prepare homeotropic alignment-showing discotic liquid crystals. Very interestingly, the spherical C 60 parts form a helical structure around the column formed by the disk-like Pc parts This supramolecular structure very resembles spiranthes. The spiranthes-like supramolecular structure is compatible with one-dimensional nano-array expecting the high conversion efficiency of solar cells.