Circularly Polarized Luminescence and Circular Dichroism of Bichromophoric Difluoroboron-β-diketonates: Inversion and Enhanced Chirality Based on Spatial Arrangements and Self-Assembly

We synthesized two bichromophoric difluoroboron-β-diketonates (DFB) connected in para and meta positions by using cyclohexane diamine as a chiral bridge ( para and meta (R/S)-CyDFB ). TD-DFT calculations revealed that the variation in connectivity of the DFB units leads to different spatial arrangements and a chirality inversion of the bichromophoric DFB. Higher g_abs values were obtained in (R/S)-CyDFB connected in para as compared to meta position. Aggregation of para (R/S)-CyDFB in mixture of solvents increase the g_lum values as compared to its monomeric form. Ultrasonication and heating induced the formation of highly ordered nano-helical wires of para (R/S)-CyDFB that increased the g_lum values to 0.015. On the other hand, meta (R/S)-CyDFB failed to form highly ordered self-assembled wires due to hindered H-binding sites. These observations indicate that the chiroptical properties of DFB bi-chromophore system can be modulated with self-assembly and spatial arrangement of the chromophores.     

Synthesis,Structure, and Properties of α,β‐Linked Oligothiazoles with Controlled Sequence

α,β‐Linked oligothiazoles with head‐to‐tail connectivity are presented as a new family of helical scaffolds. Combinations of palladium‐catalyzed cross‐coupling reactions at the 5‐ and 4‐positions of 2‐phenylthiazole led to the synthesis of oligo(2‐phenylthiazoles) with ortho linkages with a variety of defined sequences. The secondary structures of the α,β‐linked oligo(2‐phenylthiazoles) showed a clear dependence on their sequences. X‐ray crystallography of the trimer, tetramer, and hexamer with head‐to‐tail connection revealed the formation of a helical structure, which was stabilized by a combination of intramolecular forces, including interheteroatom (S???N), CH–π, and π–π interactions. The introduction of a chiral end‐group successfully led to the induction of chirality into the helical conformations. Programmable sequences for controlled geometries and photofunctions have been demonstrated through the manifold connection pathways in α,β‐linked oligothiazoles.     

Effect of ligand substituents in olefin polymerisation by half-sandwich titanium complexes containing monoanionic iminoimidazolidide ligands-MAO catalyst systems

Various half-sandwich titanium complexes containing iminoimidazolidide ligands, CpTiCl(2)[1,3-R(2)(CH(2)N)(2)C=N] (1a-d) [R = Ph (a), 2,6-Me(2)C(6)H(3) (b), cyclohexyl (c), (t)Bu (d)], have been employed as the catalyst precursors for ethylene polymerisation, syndiospecific styrene polymerisation, and copolymerisation of ethylene with 1-hexene in the presence of MAO cocatalyst; 1d showed the highest catalytic activity for ethylene polymerisation whereas 1b showed the highest activity for syndiospecific styrene polymerisation.     

Mechano- and Photoresponsive Behavior of a Bis(cyanostyryl)benzene Fluorophore

The mechanoresponsive behavior and photochemical response of a new bis(cyanostyryl)benzene fluorophore (CSB-5) were investigated. Green fluorescence with λ_em,max of 507 nm was found for CSB-5 in chloroform solution, mirroring the behavior of a previously reported similar dye (CSB-6). Alternatively, crystalline samples of CSB-5 exhibited orange fluorescence with λ_em,max of 620 nm, attributable to excimer emission. Although the emission color change was not clearly noticeable by naked eye, CSB-5 exhibited mechanochromic luminescence, due to transformation into the amorphous state upon grinding the crystalline powder. Interestingly, rubbed films of CSB-5 prepared on glass substrates exhibited a pronounced emission color change from orange to green when exposed to UV light. This response is the result of a photochemical reaction that occurs in the amorphous state and which causes a decrease of the excimer emission sites so that the emission color changes from excimer to monomer. The crystalline material did not display such a photoinduced emission color change and the difference in photochemical reactivity between crystalline and amorphous states was exploited to pattern the emission color of rubbed films.     

Synthesis and crystal structures of phenylalanine ester-introduced palladium(II) and platinum(II) complexes and their cytotoxicities

Research on Chemical Intermediates - Phenylalanine ester-introduced palladium(II) and platinum(II) complexes were synthesized. Taking advantage of the formation of Schiff bases by amino acids as an...     

Pseudorotaxane structure of a fullerene derivative--cyclodextrin 1:2 complex

X-Ray crystallography revealed that the C(60) derivative·γ-cyclodextrin (γ-CDx) complex has a pseudorotaxane structure and the structure of the crystal clarified the importance of multi-point hydrogen bonds between two γ-CDxs for stabilising the 3·γ-CDx complex.     

Synthesis of Titanatranes Containing Bis(aryloxo)-(alkoxo)amines and their Use in Catalysis for Ethylene Polymerization

Syntheses of titanatranes containing [(O-2,4-Me₂C₆H₂-6-CH₂)₂-{O(CH₂)_nCH₂}]N³⁻ (n = 1,2) have been explored. Catalytic activity for ethylene polymerization by Ti₂(OⁱPr)₂{[(O-2,4-Me₂C₆H₂-6-CH₂)₂(µ₂-OCH₂-CH₂)]N}₂ ( 1a ) - MAO catalyst increased at high temperature; the activity also increased upon addition of AlMe₃. Ti(O- 2,6-ⁱPr₂C₆H₃){[(O-2,4-Me₂C₆H₂-6-CH₂)₂(OCH₂CH₂)]N} ( 1c ) showed higher activity than 1a under the same conditions. Ti{[(O-2,4-Me₂C₆H₂-6-CH₂)₂(HOCH₂CH₂CH₂)]N}₂ was isolated from the reaction of Ti(OⁱPr)₄ with bis(2-hydroxy-3,5-dimethylbenzyl)-propanolamine; the structure was determined by X-ray crystallography.