PREDICTED WEAK DISTANCE DEPENDENCE OF THROUGH-BOND MEDIATED ELECTRONIC COUPLING IN N-ALKANE BRIDGES - AN ABINITIO MOLECULAR-ORBITAL STUDY

Pi+,pi- and pi+*,pi-* splittings for a series of divinylalkanes, CH2=CH(CH2)pCH=CH2, and diethynylalkanes, HCL=C(CH2)pC=CH, were obtained in the Koopmans' theorem approximation using the 3-21 G basis set. The pi+,pi- splittings for the divinyl molecules follow approximately an exponential decay with increasing number (n) of C-C bonds: DELTAE(pi) = A exp(-betan), with beta almost-equal-to 0.26 per bond. In contrast, the beta value between successive members in the diethynyl series steadily diminishes with increasing chain length, down to a value of only 0.11 per bond for the longest members studied (p = 22, 23). These results suggest that all-trans alkyl chains should be extremely effective mediators of rapid hole transfer over large distances (>21 angstrom).