Intrinsic room-temperature electrophosphorescence from a pi-conjugated polymer

Electrically induced phosphorescence from a poly(para-phenylene) ladder-type polymer is observed for the first time and characterized using time resolved spectroscopy. Short-lived phosphorescence is also observed in gated fluorescence spectra and is found to be quenched reversibly by oxygen. Thermally activated triplet diffusion to covalently bound palladium sites, which are formed at a concentration of about 80 ppm in a side reaction during polymer synthesis, is believed to be the cause of this novel effect, which suggests a new approach to the design of efficient electroluminescent materials.     

Zur Beeinflussung des Hagelkornwachstums

Summary To decrease the accretion rate of a growing hailstone its deposit has to be made dry. Under such conditions a spherical form is prefered to an ellipsoidal one. The growth rate of the former is lower than that of the latter to a factor of two. The accretion rate can be slowed down further when the small cloud particles are partially frozen. In a solid state they will mostly be rejected from the surface of the (dry) hailstone and do not contribute to growth.In paragraph 4 calculations are made about the proportion of cloud particlesV which must be frozen to arrive at a dry deposit. The variables are air temperaturet _L , hailstone diameterd, free H₂O-contentw _f , and air pressurep. The results are shown in Figures 1, 2, and 3 and demonstrate the high ratio of cloud droplets which should be frozen to reduce the growth rate noticeably. Figure 4 is valuable for hailstones growing in a cloud model as postulated byLudlam.This decrease in accretion rate will normally lower the hail damage. But there exists another method which produces hailstones with a very high rate of liquid water. Such spongy particles burst as soon as they hit the ground. The conditions for such a procedure are not yet elaborated but are quite dissimilar to those described above.     

Quantum mechanical predictions of the stereoselectivities of proline-catalyzed asymmetric intermolecular aldol reactions

Quantum mechanical calculations were employed to predict the ratio of four stereoisomeric products expected from two complex reactions involving the aldol reactions of cyclohexanone with benzaldehyde or with isobutyraldehyde catalyzed by (S)-proline. Experimental tests of these predictions provide an assessment of the state-of-the-art in quantum mechanical prediction of products of complex organic reactions in solution.     

Catalytic Asymmetric Reductive Condensation of N–H Imines: Synthesis of C2‐Symmetric Secondary Amines

A highly diastereoselective and enantioselective Brønsted acid catalyzed reductive condensation of N?H imines was developed. This reaction is catalyzed by a chiral disulfonimide (DSI), uses Hantzsch esters as a hydrogen source, and delivers useful C₂‐symmetric secondary amines.     

Catalytic asymmetric intramolecular alpha-alkylation of aldehydes

The development of a general catalytic asymmetric aldehyde alpha-alkylation reaction constitutes a major challenge in organic synthesis. Here, we report the first and successful approach toward its solution: (S)-alpha-methyl proline catalyzes the intramolecular alkylation of various halo aldehydes to the corresponding formyl cyclopentanes, -cyclopropanes, or -pyrrolidines in excellent yields and enantioselectivities. Most remarkably, racemization, aldolization, or catalyst alkylation do not occur to any significant extend, further illustrating the power, mildness, and profound selectivity of enamine catalysis.     

Design and Enantioselective Synthesis of Cashmeran Odorants by Using “Enol Catalysis”

Novel Cashmeran odorants were designed by molecular modeling. Their short syntheses involve a novel asymmetric Brønsted acid catalyzed Michael addition of unactivated α‐substituted ketones. This key transformation was realized by utilizing a new type of enol activation catalysis and affords different cyclic ketones bearing α‐quaternary stereocenters in good to excellent yields and with high enantioselectivity. Subsequent McMurry coupling and Saegusa–Ito oxidation furnished the enantiopure target odorants, one enantiomer of which indeed possesses the typical olfactory aspects of Cashmeran.