Showing papers on "Substituent published in 2013"
TL;DR: With internal olefins, the cobalt catalyst places the boron substituent exclusively at the terminal positions of an alkyl chain, providing a convenient method for hydrofunctionalization of remote C-H bonds.
Abstract: Bis(imino)pyridine cobalt methyl complexes are active for the catalytic hydroboration of terminal, geminal, disubstituted internal, tri- and tetrasubstituted alkenes using pinacolborane (HBPin). The most active cobalt catalyst was obtained by introducing a pyrrolidinyl substituent into the 4-position of the bis(imino)pyridine chelate, enabling the facile hydroboration of sterically hindered substrates such as 1-methylcyclohexene, α-pinene, and 2,3-dimethyl-2-butene. Notably, these hydroboration reactions proceed with high activity and anti-Markovnikov selectivity in neat substrates at 23 °C. With internal olefins, the cobalt catalyst places the boron substituent exclusively at the terminal positions of an alkyl chain, providing a convenient method for hydrofunctionalization of remote C-H bonds.
282 citations
TL;DR: BF2bdks exhibit comparable fluorescence properties in both solutions and polymers when the diketonate group is functionalized with smaller aromatic ring systems such as benzene, but emission from a strong intramolecular charge-transfer state was also noted in both solution and in PLA.
Abstract: Aromatic difluoroboron β-diketonate complexes (BF2bdks) are classic fluorescent molecules that have been explored as photochemical reagents, two-photon dyes, and oxygen sensors. To gain a better understanding of their emissive properties in both solution and polymer matrices, BF2bdks with varying aromatic groups were synthesized and their photophysical properties were investigated in both methylene chloride and poly(lactic acid) (PLA). Absorption spectra showed systematic variations that are well correlated with structural features, including the size of the aryl substituent and the presence of a para electron-donating methoxy substituent. Computational modeling of the absorption spectra with the TD-B3LYP/6-311+G(d)//B3LYP/6-31G(d) formulation of density functional theory and a polarizable continuum model of dichloromethane solvent shows that all systems show intense π–π* one-electron excitations, usually from one of the highest occupied molecular orbitals (HOMO – k, k = 0, 1, 2) to the lowest unoccupied ...
161 citations
TL;DR: The first total synthesis of drimentines A, G, and F (1–3) is reported, exploiting a photocatalyzed radical conjugate addition to address the problem of the C10b–C12 bond formation.
Abstract: The pyrroloindoline alkaloids attract wide interest from the fields of chemistry, biosynthesis, and biology. From a structural perspective, they can be divided into several classes that vary in the substituent on C3a of the pyrroloindoline core, including heteroatoms, arenes, aliphatic groups, and another pyrroloindoline motif. Accordingly, a series of strategies have been developed for the synthesis of the above pyrroloindoline classes. Notably, a structurally complex aliphatic side chain linked to the C3a position is rather rare. The drimentine alkaloids (1–4, Scheme 1), which exhibit anticancer, antibacterial, antifungal, and anthelmintic properties, possess the latter substitution mode. A stereocontrolled method to form the C10b–C12 bond of the drimentine scaffold is highly desired for the synthesis of these compounds. Indotertine A (5, Scheme 1) with an unprecedented, but biosynthetically relevant, skeleton was recently discovered. The biosynthetic relationship between 3 and 5 is postulated in Scheme 1. Acidic activation of the germinal diamine moiety of 3 may generate an iminium species 6, which could undergo an iminium–olefin cyclization followed by a proton elimination of the cationic intermediate 7. Herein, we report the first total synthesis of drimentines A, G, and F (1–3), exploiting a photocatalyzed radical conjugate addition to address the problem of the C10b–C12 bond formation; a synthesis of indotertine A (5), guided by the above biosynthetic hypothesis, is also described. We first undertook a retrosynthetic analysis of drimentine G (Scheme 2). Disassembly of the diketopiperazine motif at the amide bonds followed by cleavage of the exocyclic C=C bond simplifies this molecule to core structure 8. Disconnection of the C10b–C12 bond leads to a pair of precursors (9 and 10) for an intermolecular radical conjugate addition. The former is readily available from bis(Boc-l-tryptophan) methyl ester (Boc= tert-butoxycarbonyl), whereas the latter could be derived from commercially available (+)-sclareolide (11). Scheme 1. Representative drimentine alkaloids and the postulated biosynthetic relationship between drimentine F and indotertine A.
107 citations
TL;DR: Compound 8h, with an optimum alkyl chain length and a chloro substituent at the C-5 position of the isatin ring, displayed the best activity among the test compounds, with IC50 value of 1.21 μM against cultured W2-strain Plasmodium falciparum.
106 citations
TL;DR: In this article, the authors provide details of the recent progress in heavier Group 2-catalyzed small molecule transformations mediated by well-defined heteroleptic and homoleptic complexes of the form LMX or MX2.
Abstract: This chapter provides details of the recent progress in heavier Group 2-catalyzed small molecule transformations mediated by well-defined heteroleptic and homoleptic complexes of the form LMX or MX2, where L is a monoanionic ligand and X is a reactive σ-bonded substituent and M = Mg, Ca, Sr, and Ba. The intra- and intermolecular heterofunctionalization (hydroamination, hydrophosphination, hydrosilylation, hydroboration, hydrogenation, and hydroacetylation) of alkenes, alkynes, dienes, carbodiimides, isocyanates, pyridines, quinolines, and ketones is discussed, along with the dimerization of aldehydes, the trimerization of isocyanates, and the dehydrogenation of amine-boranes and the dehydrogenative coupling of amines with silanes. While studies in this field have focused largely on biocompatible and inexpensive catalysts of calcium and the heavier elements, the field has renewed interest in the chemistry of organomagnesium complexes.
99 citations
TL;DR: In this paper, a novel catalytic C-H activation route to privileged dibenzo[a,e]pentalene (DBP) structures has been established in the presence of PdCl2, AgOTf, and o-chloranil.
Abstract: A novel catalytic C–H activation route to privileged dibenzo[a,e]pentalene (DBP) structures has been established. In the presence of PdCl2, AgOTf, and o-chloranil, a C–H/C–H annulation of arylacetylenes takes place to furnish the corresponding DBPs. A number of mechanistic experiments indicate that this new annulation occurs through alkyne-directed, ortho-selective, electrophilic aromatic C–H palladation. Not only symmetric diarylacetylenes but also unsymmetric arylacetylenes are applicable to this reaction. UV-vis absorption spectra and DFT studies on the resulting DBPs indicate a strong substituent effect on the energy levels of the HOMO and HOMO−1 of DBPs.
98 citations
TL;DR: R'-substituents have little influence on the efficiency and chemoselectivity of the catalytic activity of the complexes, but the selectivity toward olefin cis-dihydroxylation is enhanced for complexes with R = Me, F, or Cl.
Abstract: A family of iron complexes with the general formula [FeII(R,R′Pytacn)(X)2]n+ is described, where R,R′Pytacn is the tetradentate ligand 1-[(4-R′-6-R-2-pyridyl)methyl]-4,7-dimethyl-1,4,7-triazacyclononane, R refers to the group at the α-position of the pyridine, R′ corresponds to the group at the γ-position, and X denotes CH3CN or CF3SO3. Herein, we study the influence of the pyridine substituents R and R′ on the electronic properties of the coordinated iron center by a combination of structural and spectroscopic characterization using X-ray diffraction, 1H NMR and UV–vis spectroscopies, and magnetic susceptibility measurements. The electronic properties of the substituent in the γ-position of the pyridine ring (R′) modulate the strength of the ligand field, as shown by magnetic susceptibility measurements in CD3CN solution, which provide a direct indication of the population of the magnetically active high-spin S = 2 ferrous state. Indeed, a series of complexes [FeII(H,R′Pytacn)(CD3CN)2]2+ exist as mixture...
96 citations
TL;DR: It was found that the tuning of emission color of the isophorone-based compounds in the solid state could be conveniently accomplished by changing the terminal substituent group, suggesting that substituents have a great influence on their molecular packing, electronic structure, and aggregation-induced emission properties.
Abstract: A series of new isophorone derivatives (1–5), incorporating the heterocyclic ring or aza-crown-ether group, with large Stokes shifts (>140 nm), have been synthesized and characterized. 1–4 display aggregation-induced emission behaviors, while dye 5 is highly emissive in solution but quenched in the solid state. It was found that the tuning of emission color of the isophorone-based compounds in the solid state could be conveniently accomplished by changing the terminal substituent group. The photophysical properties in solution, aqueous suspension, and crystalline state, along with their relationships, are comparatively investigated. Crystallographic data of 1–4 indicate that the existence of multiple intermolecular hydrogen bonding interactions between the adjacent molecules restricts the intramolecular vibration and rotation and enables compounds 1–4 to emit intensely in the solid state. The size and growth processes of particles with different water fractions were studied using a scanning electron micro...
84 citations
TL;DR: In this article, the electrogeneration of aryl radicals from protected diazonium salts combined with protection-deprotection steps was evaluated to design functional monolayers on carbon substrates with a well-controlled organization at the nanometric scale.
Abstract: The electrogeneration of aryl radicals from protected diazonium salts combined with protection–deprotection steps was evaluated to design functional monolayers on carbon substrates with a well-controlled organization at the nanometric scale. The structure of the obtained monolayer is adjusted by varying the size of the protecting group that is introduced on the precursors (trimethylsilyl, triethylsilyl, and tri(isopropyl)silyl were tested in the present study). After deprotection, a robust ethynylaryl monolayer is obtained whatever the substituent that serves as a platform to attach other functional groups by a specific “click chemistry” coupling step. Electrochemical and structural analyses show that the organization of the attached monolayer is totally governed by the size of the protecting group that leaves a footprint after removal but maintains a total availability of the immobilized functional groups. Properties of the monolayer (charge transfer, permeation of molecules through the layer, density of...
82 citations
TL;DR: In this article, a series of indole and 5-methoxyindole derivatives, substituted at C3 with n -propyl or 4-methylcyclohexyl scaffolds bearing varying degrees of fluorination of the terminal methyl group, have been prepared and studied.
82 citations
TL;DR: Density functional theory calculations were used to predict and rationalize the effect of the modification of the structure of the prototype 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) N-heterocyclic carbene (NHC) ligand.
Abstract: Density functional theory (DFT) calculations were used to predict and rationalize the effect of the modification of the structure of the prototype 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) N-heterocyclic carbene (NHC) ligand. The modification consists in the substitution of the methyl groups of ortho isopropyl substituent with phenyl groups, and here we plan to describe how such significant changes affect the metal environment and therefore the related catalytic behaviour. Bearing in mind that there is a significant structural difference between both ligands in different olefin metathesis reactions, here by means of DFT we characterize where the NHC ligand plays a more active role and where it is a simple spectator, or at least its modification does not significantly change its catalytic role/performance.
TL;DR: A general equation, which makes possible an estimate of β(11-1) for any pair of boronic acid and diol from their pKa values, is proposed on the basis of established Brönsted-type correlation of Hammett parameters with acidity of diols.
Abstract: Stability constants of boronic acid diol esters in aqueous solution have been determined potentiometrically for a series of meta-, para-substituted phenylboronic acids and diols of variable acidity...
TL;DR: The mechanism, solvent effects, and origins of selectivities in Ru(II)-catalyzed intramolecular (5+2) cycloaddition and ene reaction of vinylcyclopropanes (VCPs) and alkynes have been studied using density functional theory.
Abstract: The mechanism, solvent effects, and origins of selectivities in Ru(II)-catalyzed intramolecular (5+2) cycloaddition and ene reaction of vinylcyclopropanes (VCPs) and alkynes have been studied using density functional theory. B3LYP/6-31G(d)/LANL2DZ optimized structures were further evaluated with the M06 functional, 6-311+G(2d,p) and LANL2DZ basis sets, and the SMD solvent model. The favored mechanism involves an initial ene-yne oxidative cyclization to form a ruthenacyclopentene intermediate. This mechanism is different from that found earlier with rhodium catalysts. The subsequent β-hydride elimination and cyclopropane cleavage are competitive, determining the experimental selectivity. In trans-VCP, the cyclopropane cleavage is intrinsically favored and leads to the (5+2) cycloaddition product. Although the same intrinsic preferences occur with the cis-VCP, an unfavorable rotation is required in order to generate the cis-double bond in seven-membered ring product, which reverses the selectivity. Acetone solvent is found to facilitate the acetonitrile dissociation from the precatalyst, destabilizing the resting state of the catalyst and leading to a lower overall reaction barrier. In addition, the origins of diastereoselectivities when the allylic hydroxyl group is trans to the bridgehead hydrogen are found to be the electrostatic interactions. In the pathway that generates the favored diastereomer, the oxygen lone pairs from the substituent are closer to the cationic catalyst center and provide stabilizing electrostatic interactions. Similar pathways also determine the regioselectivities, that is, whether the more or less substituted C-C bond of cyclopropane is cleaved. In the trans-1,2-disubstitued cyclopropane substrate, the substituent from the cyclopropane is away from the reaction center in both pathways, and low regioselectivity is found. In contrast, the cleavage of the more substituted C-C bond of the cis-1,2-disubstituted cyclopropane has steric repulsions from the substituent, and thus higher regioselectivity is found.
TL;DR: In this article, the reaction of diarylalkylsilanes and Germanes with trityl cation in the presence of a weakly coordinating anion to give the corresponding triarylsilylium or -germylium ions was investigated.
TL;DR: Three new tetranuclear copper(II) complexes have been synthesized using three different hydrazone Schiff base ligands derived from the condensation of the aromatic acid hydrazides 2-hydroxybenzo-, 2-aminobenzo- or benzo-hydrazide with 2,3-dihydroxybenzaldehyde.
Abstract: Three new tetranuclear copper(II) complexes [Cu(HL1)]4·4EtOH (1·4EtOH), [Cu(HL2)]4 (2) and [Cu(H2L3)]4(NO3)4·2H2O (3·2H2O) have been synthesized using three different hydrazone Schiff base ligands derived from the condensation of the aromatic acid hydrazides 2-hydroxybenzo-, 2-aminobenzo- or benzo-hydrazide, with 2,3-dihydroxybenzaldehyde. Complexes 1 and 3 have been characterized by single crystal X-ray diffraction analysis. The coordinating behaviour of the ligand depends on the nature of the ortho substituent present in the hydrazide moiety. The ligands bearing a strong electron donating group (by resonance) in the ortho position undergo complexation via enolization and deprotonation, whereas the absence of such an effect leads to complexation via the keto form, and two different types of tetranuclear Cu(II) clusters, viz. open-cubane and cubane, are obtained. Variable temperature magnetic susceptibility measurements of complexes 1 and 3 have been carried out to examine the nature of magnetic interaction between the Cu(II) centres. All the three complexes (1–3) act as good catalyst precursors towards mild hydrocarboxylation of linear and cyclic alkanes into carboxylic acids in water–acetonitrile medium.
TL;DR: In this article, the alkyl chain orientations determined the polymer chains packing pattern in the thin films, the film morphologies, and the resulting device performances of P1-P3.
Abstract: Thieno[3,4-c]pyrrole-4,6-dione (TPD) containing copolymer semiconductors P1–P3 were strategically designed and successfully synthesized. Their physicochemical properties were thoroughly investigated. All polymers exhibited good solution processability and high humidity stability in thin film transistors (TFTs). Transistor electrical characterization showed the device performance was sensitive to the alkyl chain substituent orientations of the polymers. A maximum TFT hole mobility of ∼1.29 cm2/(V s) was observed for P3-based devices, a recorded mobility for TPD containing polymer semiconductors reported to date. The corresponding thin-film morphologies and polymer chains packing were investigated in detail by AFM and 2D-GIXD to correlate with the alkyl orientation-dependent carrier mobility of P1–P3. Experimental results showed the alkyl chain orientations determined the polymer chains packing pattern in the thin films, the film morphologies, and the resulting device performances of P1–P3.
TL;DR: In this article, a saturated abnormal N-heterocyclic carbene complex of gold was prepared by a 1,3-dipolar cycloaddition of an in situ generated azomethine ylide with an isocyanogold(I) choride.
TL;DR: In this paper, a family of electronically tuned fac-Re(CO)3Cl pyridyl-1,2,3-triazole complexes have been synthesized by refluxing methanol solutions of [Re( CO)5Cl] and the substituted 2-(1-R-1H-1 2,3,triazol-4-yl)pyridine ligands (pytri-R) were characterised by elemental analysis, HR-ESMS, IR, 1H and 13C NMR.
TL;DR: In this paper, the effect of the substituent group of an organic ligand on the structures of coordination polymers was investigated and characterized by single-crystal X-ray diffraction.
Abstract: In order to investigate the effect of the substituent group of an organic ligand on the structures of coordination polymers, four new Ni(II) coordination polymers based on 5-position substituted 1,3-benzenedicarboxylate and N-donor auxiliary ligands, namely, [Ni(5-CH3-ip)(L1)(H2O)]n (1), [Ni(5-NO2-ip)(L1)2(H2O)]n (2), [Ni(5-CH3-ip)(L2)1.5]n (3) and {[Ni2(5-NO2-ip)2(L2)2(H2O)2]·(H2O)}n (4) (5-CH3-ip = 5-methyl-1,3-benzenedicarboxylic acid, 5-NO2-ip = 5-nitro-1,3-benzenedicarboxylic acid, L1 = 1,4-bis(imidazol-1-yl)benzene and L2 = 1,4-bis(1-imidazol-yl)-2,5-dimethyl benzene), have been synthesized and characterized by single-crystal X-ray diffraction. Complex 1 features a two-dimensional (2D) layer structure. Complex 2 possesses a three-dimensional (3D) 5-connected net giving an interesting 3-fold interpenetrating architecture. Complex 3 shows a 5-connected topological framework with point symbol (42.68). Complex 4 displays a 6-connected 3D self-penetrating topological network with point symbol (48.52.65). Structural diversities indicate that the substituent group of organic ligands play important roles in tuning the structures of these complexes. Furthermore, magnetic properties of complexes 1 and 4 are investigated.
TL;DR: In this paper, three new N-alkyl-N′-(2-ethyl-1-selenophenyl)imidazolium salts, L1-L3 (differing in the chain length of alkyl substituent of N), which are precursors to (Se, CNHC) ligands and their N-heterocyclic carbene (NHC) complexes [Pd(L-HX)Cl2] (1-3) [L = L1−L3, X = I/Br], have
TL;DR: A series of novel C1-symmetric aminodiolate rare-earth-metal complexes have been prepared via arene elimination from [Ln(o-C6H4CH2NMe2)3] (Ln = Y, Lu) and the corresponding aminodoriol proligand as discussed by the authors.
TL;DR: The ligand-based concept of shortening quintuple bonds and some of its limitations are reported and a chromium-arene sandwich complex structurally related to the classic dibenzene chromium complex was observed, even when bulkier substituents are introduced at the central carbon atom of the used guanidinato ligand.
Abstract: Herein, the ligand-based concept of shortening quintuple bonds and some of its limitations are reported. In dichromium-diguanidinato complexes, the length of the quintuple bond can be influenced by the substituent at the central carbon atom of the used ligand. The guanidinato ligand with a 2,6-dimethylpiperidine backbone was found to be the optimal ligand. The reduction of its chromium(II) chloride-ate complex gave a quintuply bonded bimetallic complex with a CrCr distance of 1.7056 (12)angstrom. Its metal-metal distance, the shortest observed in any stable compound yet, is of essentially the same length as that of the longest alkane CC bond (1.704 (4)angstrom). Both molecules, the alkane and the Cr complex, are of remarkable stability. Furthermore, an unsupported Cr-I dimer with an effective bond order (EBO) of 1.25 between the two metal atoms, indicated by CASSCF/CASPT2 calculations, was isolated as a by-product. The formation of this by-product indicates that with a certain bulk of the guanidinato ligand, other coordination isomers become relevant. Over-reduction takes place, and a chromium-arene sandwich complex structurally related to the classic dibenzene chromium complex was observed, even when bulkier substituents are introduced at the central carbon atom of the used guanidinato ligand.
TL;DR: A copper(I)-catalyzed intramolecular oxidative C H bond functionalization and C N coupling of 2-aminobenzophenones to give 6-membered-ring acridone products is reported.
Abstract: A copper-catalyzed intramolecular oxidative C—H functionalization of 2-aminobenzophenone affords two regioisomeric 6-membered-ring acridones.
TL;DR: The first trans-selective [3 + 2]-cycloaddition of a new type of donor-acceptor cyclopropane with aldehydes is presented and allows for an easy access to tetrahydrofurans bearing a versatile alkyne substituent at the quarternary 2-position under very mild reaction conditions.
Patent•
08 Apr 2013TL;DR: An organic light-emitting device having a light emitting layer containing a compound represented by the general formula below has a high light emission efficiency as discussed by the authors, and the balance of R1 to R3 represents a hydrogen atom or a substituent.
Abstract: An organic light-emitting device having a light-emitting layer containing a compound represented by the general formula below has a high light emission efficiency. In the general formula, at least one of R1 to R5 represents a cyano group, at least one of R1 to R5 represents a 9-carbazolyl group, a 1,2,3,4-tetrahydro-9-carbazolyl group, a 1-indolyl group or a diarylamino group, and the balance of R1 to R3 represents a hydrogen atom or a substituent.
TL;DR: Three ruthenium complexes bearing backbone-monosubstituted CAACs were prepared and displayed dramatic improvement in catalytic efficiency not only in RCM reaction but also in the ethenolysis of methyl oleate.
TL;DR: A hydrogen bond-assisted π-π-interaction of the dimeric zwitterions is suggested to promote this aggregation mode, which is further affected by the nature of the amide substituent, enabling the formation of bundles of strands or even two-dimensional sheets.
Abstract: Derivatives of the self-complementary 2-guanidiniocarbonyl pyrrole 5-carboxylate zwitterion (1) (previously reported by us to dimerize to 1•1 with an aggregation constant of ca. >10(10) M(-l) in DMSO) aggregate in a diverse manner depending on, e.g., variation of concentration or its protonation state. The mode of aggregation was analyzed by spectroscopic (NMR, UV) and microscopic (AFM, SEM, HIM, and TEM) methods. Aggregation of dimers of these zwitterions to higher supramolecular structures was achieved by introduction of sec-amide substituents at the 3-position, i.e., at the rearward periphery of the parent binding motif. A butyl amide substituent as in 2b enables the discoid dimers to further aggregate into one-dimensional (rod-like) stacks. Quantitative UV dilution studies showed that this aggregation is strongly cooperative following a nucleation elongation mechanism. The amide hydrogen seems to be essential for this rod-like aggregation, as neither 1 nor a corresponding tert-amide congener 2a form comparable structures. Therefore, a hydrogen bond-assisted π-π-interaction of the dimeric zwitterions is suggested to promote this aggregation mode, which is further affected by the nature of the amide substituent (e.g., steric demand), enabling the formation of bundles of strands or even two-dimensional sheets. By exploiting the zwitterionic nature of the aggregating discoid dimers, a reversible pH switch was realized: dimerization of all compounds is suppressed by protonation of the carboxylate moiety, converting the zwitterions into typical cationic amphiphiles. Accordingly, typical nanostructures like vesicles, tubes, and flat sheets are formed reversibly under acidic conditions, which reassemble into the original rod-like aggregates upon readjustment to neutral pH.
TL;DR: The substituent parameters and structure-activity relationship reported here may be helpful for drug discovery utilizing the heavier group 14 elements.
Abstract: Here, we report the systematic synthesis and characterization of simple phenols bearing a trialkyl(aryl)silyl or trialkyl(aryl)germyl functional group as a hydrophobic substituent. These silicon and germanium analogues exhibited higher hydrophobicity than the corresponding carbon analogues, with a difference in log P value of approximately 0.6, independent of the alkyl(aryl) species. Trimethylsilylphenol and trimethylgermylphenol exhibited smaller pK(a) values than the corresponding carbon analogue or unsubstituted phenol, indicating that trialkylsilyl and trialkylgermyl functional groups have a negative substituent constant (σ). The trialkylsilyl- and trialkylgermylphenols exhibited more potent estrogenic activity as compared with the carbon analogues. The substituent parameters and structure-activity relationship reported here may be helpful for drug discovery utilizing the heavier group 14 elements.
TL;DR: In this article, the mesophase behavior was investigated by polarising optical microscopy and differential scanning calorimetry, and a representative example has also been characterised by X-ray diffraction (XRD) studies.
Abstract: Three new series of bent-shaped molecules with 4-chlororesorcinol, 4-bromoresorcinol or 4-fluororesorcinol as the central unit, and azobenzene with different alkoxy chain length as side arms were synthesised. The mesophase behaviour was investigated by polarising optical microscopy, and differential scanning calorimetry. A representative example has also been characterised by X-ray diffraction (XRD) studies. It is found that almost all of the materials prepared are monotropic liquid crystalline. Depending on the substituent at the central unit and on the chain length nematic phases, B6 phases, a B4-like dark conglomerate phase and a modulated/undulated anticlinic SmC phase were found. As a unique feature, upon reducing the chain length a transition from nematic to B6-type smectic phases was observed, which is reverse to usually observed phase sequences. The UV–vis absorption spectroscopy was also performed to study the effect of light-induced trans–cis-isomerisation on the prepared compounds.