Rectangular Mesophase Research Articles

Phenanthrothiophene-Triazine Star-Shaped Discotic Liquid Crystals: Synthesis, Self-Assembly, and Stimuli-Responsive Fluorescence Properties.

Lipophilic biphenylthiophene- and phenanthrothiophene-triazine compounds, BPTTn and CPTTn, respectively, were prepared by a tandem procedure involving successive Suzuki-Miyaura coupling and Scholl cyclodehydrogenation reactions. These compounds display photoluminescence in solution and in thin film state, solvatochromism with increasing solvent's polarity, as well as acidochromism and metal ion recognition stimuli-responsive fluorescence. Protonation of BPTT10 and CPTT10 by trifluoroacetic acid results in fluorescence quenching, which is reversibly restored once treated with triethylamine (ON-OFF switch). DFT computational studies show that intramolecular charge transfer (ICT) phenomena occurs for both molecules, and reveal that protonation enhances the electron-withdrawing ability of the triazine core and reduces the band gap. This acidochromic behavior was applied to a prototype fluorescent anti-counterfeiting device. They also specifically recognize Fe3+ through coordination, and the recognition mechanism is closely related to the photoinduced electron transfer between Fe3+ and BPTT10/CPTT10. CPTTn self-assemble into columnar rectangular (Colrec) mesophase, which can be modulated by oleic acid via the formation of a hydrogen-bonded supramolecular liquid crystal hexagonal Colhex mesophase. Finally, CPTTn also form organic gels in alkanes at low critical gel concentration (3.0 mg/mL). Therefore, these star-shaped triazine molecules possess many interesting features and thus hold great promises for information processing, liquid crystal semiconductors and organogelators.

Organic dyads and triads based on the triphenylene-rylenediimide couple: Molecular design, self-organization, and photo-physical properties

Liquid-crystalline D-A dyads and A-D-A triads, based on the chemical association of electron-donor (D) triphenylene discogens and electron-acceptor (A) perylene/benzoperylene diimides, have been synthesized by the Pd-catalyzed Sonogashira coupling/DBU-promoted cyclization reactions tandem. These molecular heterojunctions spontaneously self-organize into columnar hexagonal (Colhex) or/and rectangular (Colrec) mesophases, over broad temperature ranges including room temperature, with the antagonist moieties segregated into alternated homo-molecular (homolithic) stacks within mixed columns. Their intramolecular electron and energy transfers have been studied by UV/Vis absorption and fluorescence emission spectroscopies. Due to photo-induced electron transfer between donor and acceptor units, fluorescence quenching is systematically observed for all the dyads and triads. This study further reveals that perylenediimide is a stronger electron acceptor than the larger benzoperylenediimide building block. Density function theory calculations of their molecular structures and HOMO-LUMO energy levels and gaps support the experimental results and demonstrate that these donor-acceptor systems have potential applications in various optoelectronic devices.

Investigation of mesomorphic, photophysical and gelation behavior in aroylhydrazone based liquid crystals: Observation of mesophase crossover phenomena

Five series of substituted aroylhydrazones having two alkoxy chains at 3- and 5- positions at amide end of the molecule have been synthesized; wherein each series differ from each other in terms of number and position of alkoxy chains at imine end. The compounds of first series with the single alkoxy chain at 4-position at imine end self-assembled into columnar hexagonal mesophase. The lower homologues of the series with alkoxy chains at 3- and 5- positions at imine end showed a transition from columnar hexagonal to columnar rectangular mesophase in cooling cycle while the higher homologues exhibited columnar hexagonal mesophase. The series with alkoxy chains at 3- and 4- positions exhibited columnar rectangular mesophase. All the homologues of series with alkoxy chains at 2-, 3- and 4- positions showed a transition from columnar rectangular to columnar oblique mesophase in cooling cycle. The series with alkoxy chains at 3-, 4- and 5- positions exhibited transition in columnar hexagonal mesophase. The mesophase crossover from one columnar mesophase to the other was found to be dependent on the chain length as well as on the temperature during the self-assembly process in these molecules. The temperature dependent columnar mesophase crossover has been observed for the first time in these systems. The substitution pattern showed an influence on the photophysical properties. The number and position of alkoxy chains played a critical role in the formation of gel in these molecules. These liquid crystalline gelators have application potential in organic optoelectronic functional materials and devices.

Liquid crystalline oxovanadium(IV) and copper(II) complexes of halogen-substituted salphen ligands: role of metal and spacer substituents

ABSTRACT Three new series, each of hemi-discoid oxovanadium(IV) and copper(II) complexes based on halogen-substituted ‘salphen’ type ligands; H2L = [N,N-Bis(4-n-alkoxysalicylidene)-4-fluoro/chloro/bromo-1,2-diaminobenzene] (n = 12, 14, 16) have been accessed and their mesomorphic properties investigated. The complexes have been characterised by elemental analyses, FT-IR and absorption spectroscopy. The fluoro and the chloro substituted oxovanadium(IV) complexes display thermotropic columnar rectangular mesophases with a p2mm symmetry. On the contrary, the bulky bromo substituted oxovanadium(IV) complexes decompose at a high temperature precluding any mesomorphic study. The analogous copper(II) complexes also undergo decomposition on heating and are non-mesomorphic. Molecular arrangements in the mesophases have been proposed based on variable temperature powder X-ray diffraction (PXRD) study. The influence of metal’s coordination and electronegativity and/or steric hindrance of the spacer’s substituent on the mesomorphic properties of the complexes is discussed. Density functional theory (DFT) calculations carried out using the GAUSSIAN 09 program on representative oxovanadium(IV) and copper(II) complexes indicated a distorted square-pyramidal geometry around the VO(IV) centre and a distorted square planar geometry around the Cu(II) centre in their complexes.

Effect of alkoxy chain density on the mesogenic properties of aroylhydrazone based liquid crystals: synthesis, characterisation, photophysical and gelation behaviour

ABSTRACT Three series of ester linkage containing aroylhydrazone based compounds have been synthesised where density and length of alkoxy chains are varied sequentially at ester end, keeping amide end of the molecule the same to investigate the effect of alkoxy chain density. The series of the compounds with single alkoxy chain at 4- position at ester terminal show nematic mesophase. The series with two alkoxy chains at 3- and 5- positions exhibit columnar rectangular mesophase and the series with three alkoxy chains at 3-, 4- and 5- positions show columnar oblique mesophase. It was observed that increasing the number of alkoxy chains at ester terminal, self-assembly of molecules changes and leads to a change from nematic to columnar mesophase and also significant enhancement in the mesomorphic range. Temperature dependent Raman studies confirm the presence of intermolecular hydrogen bonding which assist the self-assembly and gelation properties of molecules. All the series show similar photophysical properties despite the fact that the series vary in their molecular structures. Representative compounds of each series exhibited gelation in hydrocarbon solvents. FESEM images of the gels showed interwoven network of nanofibers of several micrometres length. These supergelators may be good candidates for applications in electronic devices.

Effect of regioisomerism on the self-assembly, photophysical and gelation behavior of aroylhydrazone based polycatenars: Synthesis and characterization

In this paper we report five series of aroylhydrazone based polycatenars differing from each other in number and position of alkoxy chains on one end of the core; keeping other end the same. A systematic variation in the structures was carried out to understand the effect of position and chain length on the mesophase behavior. In the case of single alkoxy chain at 4-position, there is a transition from Smectic C to Smectic A mesophase during cooling and Smectic A to Smectic C transition in heating cycle in all the homologues except n = 6 & n = 8. In the case of two alkoxy chains at 3-, 5-positions, the compounds are non-mesogenic in nature. On changing the position of alkoxy chains from 3-, 5-positions to 3-, 4-positions, intermolecular forces weaken and these compounds become liquid crystalline and show columnar rectangular mesophase resulting from the effect of regioisomerism. Moving on to the series with three alkoxy chains, it was observed that 2-, 3-, 4-trialkoxy substituted compounds exhibit columnar rectangular mesophase except lower chain length (n = 6 & 8) while 3-, 4-, 5-trialkoxy substituted aroylhydrazones show columnar rectangular mesophase; except n = 10 which shows columnar oblique mesophase. Thus it was established that on increasing density of alkoxy chains around one terminal, mesophase changes from smectic to columnar mesophase. Temperature dependent Raman studies confirm the presence of intermolecular hydrogen bonding. Further, effect of substitution pattern did not show much influence on the photophysical properties of the mesogenic series in solid and solution state. However, the non-mesogenic series showed a different absorption and emission transition from the mesogenic series in solid and solution state. Solid state fluorescence studies show almost similar emission maxima in all the series. However, it was also noticed that non-mesogenic series show maximum red shifted emission maxima in solid state as compared to that of solution. All the series showed good gelation properties with less than 1% CGC (wt%) suggesting the strong ability of molecules to form gel. These H-bonded liquid-crystalline gels have immense potential for applications in emissive displays.

Photoluminescent nickel(II)-metallomesogens derived from salphen ligands: influence of halogens at the spacer on mesomorphism and emission properties

ABSTRACTThree new series of photoluminescent nickel(II) metallomesogens, [NiL]; H2L = N,N′-Bis(4-n-alkoxysalicylidene)-4-fluoro/bromo/chloro-1,2-diaminobenzene (n = 12, 14, 16) based on ‘salphen’ ligands have been synthesised and their mesomorphic and photophysical properties explored. The complexes, isolated as orange microcrystalline solids were characterised by elemental analyses, FT-IR, 1H NMR and UV-visible spectroscopy. Thermal studies show all the compounds to be enantiotropic liquid crystals displaying columnar mesophase over a wide temperature range. Electronegativity and steric requirement of the halogen substituent at the ligand’s spacer remarkably influence the 2-D packing of the columns in the lattice in these complexes controlling the supramolecular mesomorphic order and photoluminescence. The mesophase behaviour of the fluoro-substituted complex is characterised by a transition from a columnar oblique (p1) to columnar rectangular (p2mm) phase, former stable till ambient temperature. The chloro and bromo analogues, on the other hand, displayed exclusively columnar rectangular (p2mm) mesophase with the former transforming into a glassy state and latter into a crystalline phase during cooling to ambient temperature. Molecular model based on interdigitated anti-parallel and back to back arrangements in the different columnar mesophase are proposed on the basis of X-ray diffraction (XRD) studies. The complexes emit in the blue region when excited with near UV wavelength.

TNF Induced Switching of Columnar Rectangular to Hexagonal Assemblies in a New Class of Triphenylene-Based Room Temperature Discotic Liquid Crystals.

A straightforward synthesis of triphenylene-based oligomeric systems that self-organize into room temperature columnar structures is presented. The compounds with longer spacer length (m = 10 and 12) exhibit columnar rectangular (Colr) mesophase whereas the compound with m = 8 exists in glassy Colr state. Interestingly, the Colr self-assembly of these compounds switches to columnar hexagonal (Colh) on doping the compounds with 2,4,7-trinitrofluorenone (TNF). For the dopant concentration of 1:1 with respect to native compound, an intermediate transition state between Colr and Colh phase was observed which completely transformed into the hexagonal phase on increasing the concentration to 1:2 (compound: TNF) and afterward. Both the Colr and Colh self-assemblies have been well resolved by detailed X-ray analysis. These kind of oligomeric compounds generally possess a combination of desirable alignment properties analogous to monomeric compounds and long-lived glassy states similar to that of polymeric mesogens. In addition, charge hopping behavior is expected to increase in these compounds due to donor-acceptor interactions. Overall, these compounds can find possible potential applications in semiconductor devices.

Unsymmetrically substituted room temperature discotic liquid crystals based on hexa–peri–hexabenzocoronene core

AbstractThe first discotic system based‐on alkoxy (tri‐ & di‐) substituted hexa‐peri‐hexabenzocoronene (HBC) that self‐organizes into room temperature columnar structure is reported. Tri‐ and di‐ substituted HBC derivatives showed reddish and yellowish green fluorescence under long wavelength (365 nm) UV light illumination in solution as well as in thin films in the liquid crystalline (LC) state at room temperature, respectively. Thermotropic LC behavior of these compounds was studied by differential scanning calorimetry, polarized optical microscopy and small‐ and wide‐angle X‐ray scattering. Tri‐alkoxy derivative was found to self‐organize into a highly ordered columnar rectangular mesophase, while the other (di‐) possessed a columnar hexagonal mesophase, indicating that in spite of their non‐planarity, the aromatic cores in the mesophase are tightly packed to give highly ordered phases. This system is a promising candidate as an active component of organic light emitting devices, due to its facile processability, low band gap, luminescence and exceptionally higher ordered self‐organization behavior in the mesophase derived from X‐ray scattering studies.

Triphenylene-Based Room-Temperature Discotic Liquid Crystals: A New Class of Blue-Light-Emitting Materials with Long-Range Columnar Self-Assembly.

A straightforward synthesis of multialkynylbenzene-bridged triphenylene-based dyad systems (via flexible alkyl spacers) that self-organize into room-temperature columnar structures over a long range is reported. The compounds with spacer lengths (n) of 8 and 10 exhibit a columnar rectangular mesophase whereas a compound with n = 6 shows a columnar rectangular plastic phase. Interestingly, the later compound (n = 6) shows the formation of well-nucleated spherulites of about several hundred micrometers that suggest the existence of a long-range uniform self-assembly of columns. All of these compounds show blue luminescence in solution and in the thin-film state under long-wavelength (365 nm) UV light. These compounds fulfill the described demands such as long-range columnar self-assembly at room temperature, a good yield with high purity, and blue-light emitters under the neat condition for possible potential applications in semiconductor devices. They also match the criteria of facile processing from the isotropic state because of their low isotropization temperature. This new class of materials is promising, considering the emissive nature and stabilization of the columnar mesophase at ambient temperature.

Plank-shaped column-forming mesogens with substituents on one side only.

Prolonged glyoxylation of pyrenyl-1-glyoxylic acid ethyl ester leads to a mixture of isomers with polar pyrenylene-1,8-diglyoxylic acid as the main product, whereas the centrosymmetric 1,6-isomer is obtained in good yield from the corresponding dibromopyrene. Perkin condensations followed by Pd-catalyzed cyclizations lead to isomeric dinaphthopyrene-tetracarboxdiimides that self-assemble into columnar liquid crystals of hexagonal and rectangular symmetry, of which the rectangular mesophases have unusually elongated unit cells. The cisoid diimides with both alkylimide substituents on the same side of the oblong arene system show a much greater tendency to self-assemble into fluid stacks of disks than their centrosymmetric isomers. With racemically branched alkyl substituents, uniform vertical surface alignment of the columns in the high-temperature hexagonal mesophase is resilient to cycling through the lower-temperature rectangular and crystalline phases.

Syntheses and Properties of Graphyne Fragments: Trigonally Expanded Dehydrobenzo[12]annulenes

We present herein the synthesis and properties of the largest hitherto unknown graphyne fragment, namely trigonally expanded tetrakis(dehydrobenzo[12]annulene)s (tetrakis-DBAs). Intramolecular three-fold alkyne metathesis reactions of hexakis(arylethynyl)DBAs 9 a and 9 b using Fürstner's Mo catalyst furnished tetrakis-DBAs 8 a and 8 b substituted with tert-butyl or branched alkyl ester groups in moderate and fair yields, respectively, demonstrating that the metathesis reaction of this protocol is a powerful tool for the construction of graphyne fragment backbones. For comparison, hexakis(arylethynyl)DBAs 9 c-g have also been prepared. The one-photon absorption spectrum of tetrakis-DBA 8 a bearing tert-butyl groups revealed a remarkable bathochromic shift of the absorption cut-off (λcutoff ) compared with those of previously reported graphyne fragments due to extended π-conjugation. Moreover, in the two-photon absorption spectrum, 8 a showed a large cross-section for a pure hydrocarbon because of the planar para-phenylene-ethynylene conjugation pathways. Hexakis(arylethynyl)-DBAs 9 c-e and 9 g and tetrakis-DBA 8 b bearing electron-withdrawing groups aggregated in chloroform solutions. Comparison between the free energies of 9 e and 8 b bearing the same substituents revealed the more favorable association of the latter due to stronger π-π interactions between the extended π-cores. Polarized optical microscopy observations, DSC, and XRD measurements showed that 8 b and 9 e with branched alkyl ester groups displayed columnar rectangular mesophases. By the time-resolved microwave conductivity method, the columnar rectangular phase of 8 b was shown to exhibit a moderate charge-carrier mobility of 0.12 cm(2) V(-1) s(-1) . These results indicate that large graphyne fragments can serve as good organic semiconductors.

Wedge-shaped 1,2-diamidobenzenes forming columnar mesophases via hydrogen bonding

Two series of o-diamidobenzenes, bearing long-chain alkyl substituted gallic ester groups, have been synthesised. The 3,4,5,6-unsubstituted amides 7 with a minimum chain length of C9 exhibited columnar rectangular mesophases of p2mm symmetry with Z = 2. The liquid crystalline phases spread over phase width of extremely wide temperature intervals from -50 to 118°C. However, the phase width slightly decreased with an increase in the length of alkyl substituents. Despite their very similar molecular structure, 1,2-dimethoxy-4,5-diamides 10 revealed a different packing behaviour in their mesophases, due to steric factors. The diamides 10 formed columnar rectangular mesophases with p2mm symmetry, but with Z = 3. In a comparison with unsubstituted analogues 7, compounds 10 displayed even broader mesophases (with temperature intervals up to 220°C).

Photoconductive Nile red cyclopalladated metallomesogens

The synthesis and the electrochemical, photophysical and photoconductive properties of two new cyclometallated metallomesogens are described. These two complexes were respectively obtained by covalent metallation of Nile red, or a polyalkylated Nile red derivative, to a palladium(II) ion and by using a polyalkylated Schiff base as an ancillary ligand to complete the coordination sphere of the metal centre. The introduction of long alkyl chains on either one or both ligands leads to disk-shaped metallomesogens with ordered room temperature columnar organisation induced, in both cases, by the formation of dimeric pairs. As shown by powder X-Ray diffraction studies, both complexes exhibit a columnar rectangular mesophase over a wide temperature range. These complexes show a redox solution behaviour characterised by one reversible single-electron reduction and two consecutive reversible oxidation waves, which give them an electrochemical amphoteric character. Energy levels and distributions of frontier orbitals have been estimated. Photoconductivity of the mesophase at room temperature has been observed from UV-Vis to near IR wavelength. The high thermal, electrochemical and mesophase stabilities of the studied Nile red complexes confirm that cyclometallated Pd(II) complexes form a new class of photoconductors with features suitable for molecular semiconductor applications.

Counterion Effects on the Columnar Mesophases of Triphenylene‐Substituted [18]Crown‐6 Ethers: Is Flatter Better?

The twisted lateral tetraalkyloxy ortho-terphenyl units in dibenzo[18]crown-6 ethers 1a-f were readily converted into the flat tetraalkyloxytriphenylene systems 2a-f by oxidative cyclization with FeCl(3) in nitromethane. Reactions of the latter with potassium salts gave complexes KX.2, which displayed mesomorphic properties. The aromatization increased both the clearing and melting points; the mesophase stabilities, however, were mainly influenced by the respective anions upon complexation with various potassium salts. In contrast, the alkyl chain lengths played only a secondary role. Among the potassium complexes of triphenylene-substituted crown ethers KX.2, only those with the soft anions I(-) and SCN(-) displayed mesophases with expanded phase temperature ranges of 93 degrees C and 132 degrees C (for KX.2e), respectively, as compared to the corresponding o-terphenyl-substituted crown ether complexes KI.1e (DeltaT=51 degrees C) and KSCN.1e (plastic crystal phase). Anions such as Br(-), Cl(-), and F(-) decreased the mesophase stability, and PF(6)(-) led to complete loss of the mesomorphic properties of KPF(6).2 although not for KPF(6).1. For crown ether complexes KX.2 (X=F, Cl, Br, I, BF(4), and SCN), columnar rectangular mesophases of different symmetries (c2mm, p2mg, and p2gg) were detected. In contrast to findings for the twisted o-terphenyl crown ether complexes KX.1, the complexation of the flat triphenylene crown ethers 2 with KX resulted in the formation of organogels. Characterization of the organogel of KI.2e in CH(2)Cl(2) revealed a network of fibers.

Desymmetrization of 3,3′‐Bis(acylamino)‐2,2′‐bipyridine‐Based Discotics: The High Fidelity of Their Self‐Assembly Behavior in the Liquid‐Crystalline State and in Solution

Two novel nonsymmetrical disc-shaped molecules 1 and 2 based on 3,3'-bis(acylamino)-2,2'-bipyridine units were synthesized by means of a statistical approach. Discotic 1 possesses six chiral dihydrocitronellyl tails and one peripheral phenyl group, whereas discotic 2 possesses six linear dodecyloxy tails and one peripheral pyridyl group. Preorganization by strong intramolecular hydrogen bonding and subsequent aromatic interactions induce self-assembly of the discotics. Liquid crystallinity of 1 and 2 was determined with the aid of polarized optical microscopy, differential scanning calorimetry, and X-ray diffraction. Two columnar rectangular mesophases (Col(r)) have been identified, whereas for C(3)-symmetrical derivatives only one Col(r) mesophase has been found. In solution, the molecularly dissolved state in chloroform was studied with (1)H NMR spectroscopy, whereas the self-assembled state in apolar solution was examined with optical spectroscopy. Remarkably, these desymmetrized discotics, which lack one aliphatic wedge, behave similar to the symmetric parent compound. To prove that the stacking behavior of discotics 1 and 2 is similar to that of reported C(3)-symmetrical derivatives, a mixing experiment of chiral 1 with C(3)-symmetrical 13 has been undertaken; it has shown that they indeed belong to one type of self-assembly. This helical J-type self-assembly was further confirmed with UV/Vis and photoluminescence (PL) spectroscopy. Eventually, disc 2, functionalized with a hydrogen-bonding acceptor moiety, might perform secondary interactions with molecules such as acids.

Columnar liquid crystalline assembly of doubly discotic supermolecules based on tetra-triphenylene-substituted phthalocyanine

A series of doubly discotic supermolecules with four triphenylene (Tp) mesogens attached to a phthalocyanine (Pc) core via flexible alkyl spacers were designed and synthesized. The samples were denoted as Pc(Tp)4. Two alkyl chain lengths (C5 and C12) in the Tp arms and two spacer lengths (C6 and C10) were used to study columnar liquid crystalline (LC) self-assemblies in Pc(Tp)4 samples. The mesophase morphology was studied by polarized light microscopy and X-ray diffraction techniques. When the spacer length was relatively long (C10), a normal hexagonal columnar structure with the unit cell dimension close to those for the parent Tp or Pc liquid crystals was observed. The Pc columns packed either randomly or in a hexagonal superlattice in the Tp matrix. When the spacer length was short (C6), the Tp arms and the Pc core were tightly coupled together, and thus the whole supermolecules stacked together to form a super-LC column. A column-in-column rectangular mesophase with unit cell dimensions close to the size of the entire supermolecule was observed.

π-Conjugated Triphenylene Twins Exhibiting Polymesomorphism Including the Nematic Phase

Novel discotic liquid crystals possessing two triphenylene (TP) mesogenic cores covalently connected via a rigid spacer, i.e., π-conjugated ethynyl- or butadiynyl-bridge, (TP twins) are reported. The TP twins are categorized by the lengths of β-substituted chains (R2 and R3) and peripheral alkoxy or branched aliphatic chains (R1 and R4). Three varieties of TP twins are prepared: A) TP twins having identical β-substituted and peripheral chains (R1 = R2 = R3 = R4), B) equivalent TP entities having a β-substituted chain (R2 = R3) and peripheral chains (R1 = R4) of different length from the β substitution, and C) TP twins with different TP entities having the same β-substituted and peripheral alkoxy chains (R1 = R2, R3 = R4). The phase behavior is characterized by differential scanning calorimetry (DSC), polarizing optical microscopy (POM) and X-ray diffraction (XRD) studies. These TP twins exhibit a discotic nematic (N) and/or columnar rectangular (Colr) mesophases over a wide temperature range. We found that the relative length of rigid spacer and β-substituted alkoxy chains play an important role in the creation of the molecular self-assembly and formation of the mesophases. To the best of our knowledge, this is the first report of TP twins exhibiting polymesomorphism.

Guanidinium Chlorides with Triphenylene Moieties Displaying Columnar Mesophases

Novel guanidinium chlorides 6a−f which are tethered to a pentaalkyloxytriphenylene unit have been prepared by a five-step sequence from hexaalkyloxytriphenylenes 1a−f. The mesomorphic properties of 6a−f were studied by DSC, POM, and X-ray diffraction. Columnar rectangular mesophases were found for derivatives 6b−f with long alkyl chains. Detailed SAXS experiments revealed a change of the common Colr (C2/m) phase to Colr (P2m) phase with increasing chain length. Derivative 6a with pentyl side chain displayed only unidentified crystalline or plastic crystalline properties.

Synthesis and mesogenic properties of β-tetrabrominated tetraalkyloxyporphyrins

A new class of 2,3,7,8-tetrabromo-5,10,15,20-tetrakis(4'-n-1-alkyloxyphenyl)porphyrins, H 2 T (4'- OC n P ) PBr 4 (n = 4,6,8,10,12,14,16 and 18) and their Cu(II) complexes have been synthesized regioselectively and their mesophase properties explored. The mesogenic properties of the porphyrins were examined by differential scanning calorimetry and optical microscopy. An increase in alkyl chain length of the mesogens, showed an increase in melting point temperature and lowering of their clearing point temperatures with the narrower mesophases. This has been ascribed to the decreased π-π interactions as evidenced from the crystal structure of H 2 T (4'- OC 6 P ) PBr 4· THF derivative. MT (4'- OC n P ) PBr 4 derivatives showed rectangular mesophases in contrast to discotic lamellar mesophases reported for the planar MT (4'- OC n P ) P mesogens.