Robust polymer colloidal crystal photonic bandgap structures

New polymeric matrices are presented that embed organic colloidal crystalline arrays (CCA's) into mechanically stable photonic bandgap structures. We achieved these new matrices either by dispersing polystyrene CCA's with high molecular weight hydrophilic polymer [poly(ethylene glycol); (PEG)] or through in situ polymerization of hydrophilic monomers (acrylamide and acrylate functional PEG variants) about the CCA. CCA-dispersed PEG matrices exhibited strong red opalescence with a narrow peak at 614 nm and were sufficiently rigid to withstand repeated mechanical deformation. Visible photonic bandgaps also were observed from free-standing CCA composites with cross-linked poly(N, N-dimethylacrylamide) matrices. The results demonstrate the technological potential for robust organic photonic crystals.     

High sensitivity and high selectivity terahertz biomedical imaging

We demonstrate two distinct emerging terahertz (THz) biomedical imaging techniques.One is based on the use of a new single frequency THz quantum cascade laser and the other is based on broadband THz time domain spectrocopy.The first method is employed to derive a metastasis lung tissue imaging at 3.7 THz with clear contrast between cancerous and healthy areas.The second approach is used to study an osseous tissue under several imaging modalities and achieve full THz spectroscopic imaging based on the freque...     

Crystal structures of 1,1′-di(methylacetato)- and 1,1′-di(chloroethoxyethyl)-2,2′-biimidazole

1,1′-Di(methylacetato)-2,2′-biimidazole, C₁₂H₁₄N₄O₄, crystallizes from methanol in the space groupP2 ₁/c, wherea=9.535(2),b=13.385(2),c=5.1208(8) Å,V=652.2(2) ų, andZ=4.1,1′-Di(chloroethoxyethyl)-2,2′-biimidazole, C₁₄H₂₀Cl₂N₄O₂, crystallizes from cyclohexane in the space groupPbca, wherea=12.372(2),b=8.959(2),c=14.840(2) Å,V=1644.9(5) ų, andZ=8. The structures were refined toR=0.041 (1380 observed reflections) andR=0.043 (3243 observed reflections), respectively. Both molecules crystallize with coplanar rings and the substituents assume atrans configuration with a center of inversion between the bridging carbon atoms.     

Electron delocalization contribution to single crystal thermal expansion of a polydiacetylene

The thermal expansion contribution due to temperature-dependent π-electron delocalization is evaluated from spectral measurements on a single crystal polydiacetylene (poly-2,4-hexadiyne-1,6-diol bisphenylurethane). The observed temperature independence of backbone associated vibrations (less than ±1 cm^?1 change in ν_C?C and ν_C?C between 25 and 90°C) implies that thermal conformational fluctuations and equilibrium defect formation (which produce a negative thermal expansion coefficient) do not measurably affect π-electron delocalization. The separation of equilibrium defects is either much longer than that of nonequilibrium defects or much longer than required to appreciably limit π-electron delocalization in an effectively defect-free polymer. Arguments presented indicate that, in the experimental temperature interval, the observed thermal expansion coefficient in the chain direction is over an order of magnitude larger than the delocalization-associated contribution.     

New chiral benzothiazine ligand and its use in the synthesis of a chiral receptor

The development of chiral ligands to direct the course and stereoselectivity of many catalytic asymmetric reactions is an important area of interest for many research groups. As part of a program examining the chemistry of 2,1-benzothiazines, we have prepared a new chiral benzothiazine ligand. This ligand can be made in as few as three steps from commercially available starting materials. Presented herein is the synthesis of the ligand along with the synthesis of a chiral molecular receptor that potentially presages a new class of chiral molecular tweezers.     

Three complexes of bis(N‐methyl­benzo­hydro­xamato‐O,O′)copper(II)

The first single‐crystal studies of three bis‐transoid Cu–hydrox­amate salts, bis(3‐methoxy‐4,N‐dimethyl­benzo­hydrox­amato‐O,O′)copper(II), [Cu(C₁₀H₁₂NO₃)₂], bis(4‐chloro‐N‐methyl­benzo­hydro­xamato‐O,O′)copper(II), [Cu­(C₈­H₇­Cl­NO₂)₂], bis(N‐methyl‐3,5‐di­nitro­benzo­hydro­xamato‐O,O′)copper(II)–chloro­form (1/2), [Cu­(C₈­H₆­N₃O₆)₂]·­2CHCl₃, are presented. The Cu atom in each of the title compounds sits at a center of inversion and displays a nearly square‐planar geometry with the hydro­xamate‐O atoms connected to it in a syn configuration. The N atoms are in a transoid configuration. Each five‐membered Cu–hydro­xamate ring is planar, thus providing evidence that a planar N atom is present in each ring. The phenyl groups are twisted with respect to the hydro­xamate group by ～40–54°. The angular strain of the sp² carbonyl oxy­gen is significant (～10° from ideal).