Kung-Lung Cheng

Polypseudorotaxane architecture of poly-bis[4-(N-benzyl- pyridinium)]piperazine-hexa-thiocyanato-di-cadmium(II) with 2-D honeycomb-like [Cd(SCN)3]nn− anionic polymeric framework

An unusual, honeycomb-like cadmium-tri-thiocyanate polymeric framework was found in the studied hybrid material of general formula (L2+)n[Cd(SCN)3]2n2n− n (3), where L2+ is bis[4-(N-benzylpyridinium)]piperazine dication. The perforated coordination net forms due to a template effect of the organic dications which reside in the holes penetrating the net in a polyrotaxane-like manner. The salt (L2+)(SCN)2·2H2O (4) was studied for comparison.

Preparation of Unconventional Dendrimers that Contain Rigid NHTriazine Linkages and Peripheral tert-Butyl Moieties for CO2-Selective Adsorption

Three unconventional dendrimers that contained rigid NH-triazine linkages and peripheral tert-butyl moieties were prepared by using a convergent approach and characterized by (1)H and (13)Cu2005NMR spectroscopy, mass spectrometry, and elemental analysis. Based on a thermogravimetric analysis study, these dendrimers were observed to display thermal stability at about 300u2009°C. The NH-triazine moiety, which possessed protonated and proton-free nitrogen sites (like the imidazole unit), displayed the capture of polarizable CO2 molecules through hydrogen-bond and/or dipole-quadrupole interactions. In addition, the adsorption of various amounts of CO2 and N2 at different pressures suggests that the dendritic pores, which arise from the stacking of the middle co-planar and rim protuberant dendrimers, Gn -N∼N-Gn (n=1-3), either swell or shrink at high pressure, thus indicating that these dendrimers may have a breathing ability.

Synthesis and Study of an N,N-Disubstituted 4-[(4-Aminophenyl)diazenyl]benzaldehyde

An N,N-disubstituted 4-[(4-aminophenyl)diazenyl]benzaldehyde (‘azo dye) with nematic phase was synthesized by reaction of the phenylpiperazine derivative with the formylbenzenediazonium salt. The salt was prepared by a simplified reaction of poly(aminobenzaldehyde) with NaNO2 in the presence of HBF4. The azo dye was further studied by crystallography. On the basis of molecular stacking identified from crystallography, the molecular modeling was carried out to explore the molecular interactions, and it was found that the attraction of two coplanar molecules with side-to-side contact is favored, and a nematic phase is thus formed during the thermal process.

A Small Change in Central Linker Has a Profound Effect in Inducing Columnar Phases of Triazine-Based Unconventional Dendrimers

Four unconventional triazine-based dendrimers have been prepared and characterized by (1) H and (13) Cu2005NMR spectroscopies, mass spectrometry, and elemental analysis. Based on DSC studies, polarizing microscopy, and powder XRD, two of these dendrimers, containing linkers with an odd number of carbon atoms, were observed to display columnar liquid-crystalline phases during thermal treatment. However, the other two dendritic analogues, containing linkers with an even number of carbon atoms, were not observed to behave correspondingly. Based on computer simulation, we reasonably assume that the dendrimers with an odd number of carbon atoms in their linkers distort their molecular shape and adopt two isomeric structures due to asymmetrical congestion. This reduces the molecular π-π face-to-face interaction, which in turn causes the dendrimers to form columnar LC phases during thermal treatment. However, the dendrimers with an even number of carbon atoms in their linkers have more symmetrical skeletons and do not display any liquid-crystalline phase upon thermal treatment. This new strategy should be applicable for eliciting the columnar liquid-crystalline properties of other types of unconventional dendrimers with rigid frameworks.

Synthesis and study of N,N-disubstituted 4-aminophenylazobenzaldehydes

A series of N , N -disubstituted 4-aminophenylazobenzaldehydes (azo dyes) were synthesized by the reaction of phenylpiperazine derivatives with 4-formylbenzenediazonium tetrafluoroborate. The salt was easily prepared by reacting poly(aminobenzaldehyde) with sodium nitrite in the presence of tetrafluoroboric acid. A representative sample was studied by crystallography, and the charge distribution of the molecule was calculated with the aim of understanding the form of molecular stacking on the basis of crystal data. The mesogenic behaviour of the azo dyes was also studied.

Converting Nonliquid Crystals into Liquid Crystals by N-Methylation in the Central Linker of Triazine-Based Dendrimers

Two triazine-based dendrimers were successfully prepared in 60-75% yields. These newly prepared dendrimers 2a and 2b containing the -NMe(CH2)2NMe- and the -NMe(CH2)4NMe- linkers between two G3 dendrons, respectively, exhibit columnar phases during the thermal process. However, the corresponding dendrimers 1a and 1b containing the -NH(CH2)2NH- and the -NH(CH2)4NH- linkers between two G3 dendrons, respectively, do not show any LC phases on thermal treatment. Computational investigations on molecular conformations reveal that N-methylation of the dendritic central linker leads dendrimers to possess more isomeric conformations and thus successfully converts non-LC dendrimers (1a and 1b) into LC dendrimers (2a and 2b).

An Unconventional Approach to Induce Liquid-Crystalline Phases of Triazine-Based Dendrons by Breaking Their Self-Assembly into Dimers.

Three triazine-based dendrons (1u2009a-c) were successfully prepared in 70-83u2009% yields. These newly prepared dendrons are found to be liquid crystalline (LC). Computational investigations on molecular conformations and dipoles of triazine-based dendrons reveal that the substituent on the central triazine unit interrupts strong dipole or H-bond interactions to avoid dimeric formation. The obtained dendrons, not favouring self-assembly into dimers but showing LC behaviours, provides evidence for an approach contrary to the conventional method of inducing LC behaviours of dendrons by dimer or trimer formation, mostly through H-bond interactions.

Synthesis and study of N,N‐disubstituted 4‐[(4‐aminophenyl)diazenyl]benzylidene‐4′‐alkylanilines

A series of N,N‐disubstituted‐4‐[(4‐aminophenyl)diazenyl]benzylidene‐4′‐alkylanilines (azo dyes) were synthesized from the reaction of the corresponding benzaldehyde with alkylanilines. These azo dyes exhibit nematic and SmC phases on heating. Their order parameter, photo‐stability and miscibility were studied by investigation of a representative sample.