Comparing charge transfer tuning effects by chemical substitution and uniaxial pressure in the organic charge transfer complex tetramethoxypyrene-tetracyanoquinodimethane

In the search for novel organic charge transfer salts with variable charge transfer degree we study the effects of two modifications to the recently synthesized donor-acceptor Tetramethoxypyrene (TMP)-Tetracyanoquinodimethane (TCNQ). One is of chemical nature by substituting the acceptor TCNQ molecules by F4TCNQ molecules. The second consists in simulating the application of uniaxial pressure along the stacking axis of the system. In order to test the chemical substitution, we have grown single crystals of TMP-F4TCNQ and analyzed its electronic structure via electronic transport measurements, ab initio density functional theory (DFT) calculations and UV/VIS/IR absorption spectroscopy. This system shows an almost ideal geometrical overlap of nearly planar molecules alternately stacked (mixed stack) and this arrangement is echoed by a semiconductor-like transport behavior with an increased conductivity along the stacking direction. This is in contrast to TMP-TCNQ which shows a less pronounced anisotropy and a smaller conductivity response. Our bandstructure calculations confirm the one-dimensional behavior of TMP-F4TCNQ with pro- nounced dispersion only along the stacking axis. Infrared measurements illustrating the CN vibration frequency shift in F4TCNQ suggest however no improvement on the degree of charge transfer in TMP-F4TCNQ with respect to TMP-TCNQ. In both complexes about 0.1 is transferred from TMP to the acceptor. Concerning the pressure effect, our DFT calculations on designed TMP-TCNQ and TMP-F4TCNQ structures under different pressure conditions show that application of uniaxial pressure along the stacking axis of TMP-TCNQ may be the route to follow in order to obtain a much more pronounced charge transfer

A Dissection of Trading Capital: Trade in the Aftermath of the Fall of the Iron Curtain

Abstract We study trade in Europe after the fall of the Iron Curtain, and show that the countries of the former Austro-Hungarian monarchy trade significantly more with one another after 1989 than predicted by a standard gravity model. This surplus trade declines linearly and monotonically over time. We suggest that the surplus comes from a mixture of increased trust, as well as better communication and information given Austria's relationship with its eastern neighbors before the wars and during isolation. Trading capital, established under Habsburg rule and maintained in the period of the Iron Curtain, seems to have survived over four decades of separation and gives an initial boost to trade. This surplus trade disappeared rapidly after 1990 as countries rearranged themselves with the new geopolitical circumstances. We document the rate of decay of these forces. Keywords: Trade, Gravity, Habsburg Empire JEL codes: F14, F15, N33, N34, N94 * This paper has been improved by the comments and suggestions of numerous colleagues and seminar participants including but not limited t