The frequency‐doubling of 820nm laser light is one of the properties of a series of nitrocalix‐[4]arenes making them suitable, in principle, for the construction of a blue laser. Derivative 1 is the most promising, since it displays the greatest hyperpolarizability and the largest dipole moment and is stable as a film in a polymer matrix for long periods.

The synthesis of a novel class of molecules for second order nonlinear optics, i.e. calix[4]arenes with extended n-systems, is described. These compounds are obtained via Wittig-Horner reactions of the formylated calix[4]arenes 5 and 6 to give the stilbene derivatives 7-9, or by diazotization of calix[4]arene, 1, followed by alkylation to give the phenylazocalix[4]arenes 11 and 12. The molecular second order nonlinear optical properties (8.) of these calix [ 41 arenes have been measured by electric field-induced second harmonic genera tion. The influence of different acceptors as well as the influence of the different conformations of the calix[4]arenes on / ?, values were determined. Surprisingly, the wavelength of the charge-transfer band A , , , is lower when 8, increases upon increasing the number of acceptors.

Communications ADVANCED MATERIALSfact, the devices could not be operated in air owing to significant degradation as a function of oxygen and/or water partial pressure. Whereas storage in air hardly changed the I-V characteristic (e.g., 40 % reduction of conductivity after 3 weeks for EC4T) and luminance or output power, operation in air led to a rapid degradation. For example, the output power decayed by a factor of five within 10 s for EC6T and within 20 s for EC7T; EC4T and ECST could not even be measured. Thus, we operated the LEDs in an inert N, atmosphere, which provided relatively stable conditions such that EC7T and EC6T showed little degradation (e.g., 25 Yo) after 15 min of operation at 2 mA. The reason for the rapid degradation in air (and also the slight degradation in a nitrogen atmosphere) is most likely oxidation of the Al electrode, which increases the barrier height and hence reduces the injection probability of electrons. The question remains why different oligothiophenes cause different degradation behavior. At present we can think of two possible answers: a) a different degree of dissociation or follow-up reactions of the oligothiophenes, perhaps at the inner electrode surface, in oxidizing atmosphere and in the presence of a current and/or electric field, and b) different diffusion velocities of 0, and/or H,O through the thin molecular film. The thermal molecular motion induced by the current may be responsible for rapid diffusion in operation while the different film morphologies (see above) may have caused the differences amongst the oligomers. More work is needed to give a clearer answer and to solve the problem of poor LED stability.Finally, we should briefly comment on the output power, which was measured by a calibrated laser power meter and is also displayed in Figure 2 for EC6T (dash-dotted curve, right hand scale). The light emission starts at voltages as low as 2.5 V (for a 160 nm thick EC6T film) and reaches a maximum around 8 V, as can be derived from the inset, which shows the power conversion (not quantum) efficiency curve. This curve varies relatively little (factor of two) as a function of voltage but has only a modest maximum of 4 x YO.(The value for EC7T is even smaller by a factor of four; the value for ECST is markedly higher but could not be measured with sufficient accuracy.) These values have not been corrected for geometric effects, for internal reflection and absorption, and for internal energy conversion processes. If estimated corrections are taken into account the values become considerably higher (by about a factor of 100) and the quantum efficiency may be 1 0~2 -1 0 -3 % . This is still very low and far from being satisfactory, in particular in view of applications. We have some evidence that the low efficiency has various causes, such as film morphology, electrode material with too high a work function, interface bonding and reactions, and the physical properties of the molecules. We believe that it can be improved by orders of magnitude if materials and preparat...

A most exciting development in supramolecular chemistry has been the design, synthesis, and evaluation of abiotic catalysts that share with natural enzymes a number of features related to efficient catalysis.[1] Our research efforts are aimed at the development of prototype supramolecular catalysts by means of a modular approach in which an efficient catalytic unit for a given reaction and a receptor unit that is complementary to a nonreacting part of the substrate are covalently connected by means of a suitable spacer.We have now considered the bis-barium(ii) complex 1´(Ba 2 ) 2 of the homoditopic ligand 1, in which two aza[18]-90 %).

No abstract