Terminal halogen-containing rod-like liquid crystals: Synthesis, self-assembly, photophysical and mechanochromism properties.

Five series of cyanostilbene-based rod-like liquid crystals containing one different terminal atom (H, F, Cl, Br and I) at one end and one terminal aliphatic chain with different numbers of carbon atoms at the other end were reported by Suzuki coupling and Knoevenagel reactions. The influence of terminal halogen atoms and terminal chain length on the self-assembly, AIE behavior, temperature-dependent emission and mechanochromism behavior was explored by POM, DSC, XRD, SEM, absorption spectra and emission spectra. All the compounds are enantiotropic liquid crystals. The lowest non-halogen substituted homologue exhibited solo N phase, but the higher non-halogen substituted homologues exhibited mesogenic transition from SmA phase to N phase upon rising temperature. All the lowest halogen substituted homologues exhibited mesogenic transition from SmA phase to N phase upon rising temperature and all the higher homologues only exhibited SmA. The distinct mesogenic phase transition could be attributed to the intermolecular interaction produced by terminal halogen and the rigidity of the terminal aliphatic chain. All the non-halogen substituted compounds and halogen substituted compounds with smaller terminal halogen atom (F, Cl and Br atom) exhibited AIE behaviors, whereas the iodinated compounds exhibited extremely weak emission in solution and aggregated states due to the heavy atoms effect. These compounds also exhibited distinct solid-state emission with blue or cyan fluorescence, which could be quenched by increasing temperature. The reversible mechanochromism behavior was also achieved in all the compounds. The mechanical force induced quench in emission in non-halogen substituted compounds and halogen substituted compounds with smaller terminal halogen atom (F, Cl and Br atom), whereas enhancement in iodinated compounds. The reversible mechanochromism behavior endowed these compounds with potential applications in rewritable paper and anti-counterfeiting. The interesting properties in these liquid crystals would be attributed to the balance of the halogen-halogen interactions, heavy atom effect, steric-hindrance effect and chain length. These investigations would be helpful to understand the relationship between chemical structures and properties.

The Influence of Positional Isomerism of Terminal Alkyl Chains on Mesomorphic and Photophysical Behavior of Unsymmetric α-cyanostilbene-based Tetracatenars.

Two series of unsymmetric α-cyanostilbene-based tetracatenars containing three hexadecyl chains at one end and one alkyl chain with varying lengths at the other end were prepared by using Suzuki coupling and Knoevenagel reactions. These tetracatenars with the terminal three hexadecyl chains, which are adjacent to the cyano group are non-mesogens, whereas the isomers with one alkyl chain, which is adjacent to the cyano group display transition from non-mesogens to monotropic hexagonal columnar liquid crystal upon elongation of the alkyl chain. This transition could be attributed to that the three hexadecyl chains which are adjacent to the cyano group decrease the interactions between π-conjugated rigid cores, hindering the formation of mesophase. In addition, weak slovatochromism implies weak ICT in both series tetracatenars. Both series isomers exhibit distinct AIE characteristics attributing to the presence of α-cyanostilbene, which could induce stereoisomerism and restricted intermolecular rotation in the aggregated state. Different mechanochromism behaviors could be achieved due to the positional isomerism of terminal alkyl chains. Therefore, tuning the position of terminal alkyl chains could give rise to distinct changes in the molecular aggregate, which provides a scheme to build multifunctional materials with diverse potentials.

Characteristics of various forms of phosphorus and their relationships in the sediments of Haizi Lake, China.

The phosphorus (P) distribution in the sediments of Haizi Lake from the middle reach of the Yangtze River region, China, was investigated using a sequential chemical extraction procedure. P forms and concentrations of sediment samples taken at 25 sites over the whole lake were measured. The relationships between various forms of P in sediments and dissolved P in the overlying water were also discussed. Results showed that the concentrations of total P (TP) in the sediments ranged from 404 to 670 mg kg⁻¹, with an average of 503 mg kg⁻¹. The exchangeable P (Ex-P), Al-bound P (Al-P), Fe-bound P (Fe-P), occluded P (Oc-P), authigenic carbonate fluorapatite + biogenic apatite + CaCO3-associated P (ACa-P), detrital apatite + other inorganic P (De-P) and organic P (Or-P) accounted for, on average, 0.52, 0.04, 10.9, 32.0, 7.4, 20.1 and 29.0% of TP, respectively. Relevance analysis indicated that Oc-P, ACa-P and De-P, as the majority forms of inorganic P, were less correlated to others. The significant correlations between Ex-P, Al-P, Fe-P, Or-P and TP suggested the probability of reciprocal transformation. It was suggested that Ex-P, Al-P, Fe-P, Or-P and TP in the sediments might be released easily to the water interface, resulting in sustained lake eutrophication.