Design and Synthesis of Multipath Compact Cyclophanes for Quantum Interference Studies

To investigate interference phenomena and conductance properties in mechanically controlled break junctions (MCBJs), macrocycles 1 and 2 (BMCs: for BenzeneMacroCycles), containing a meta-substituted benzene moiety with solubilizing tertbutyl groups, as well as structures 3 and 4 (TMCs: for ThiopheneMacroCycles), featuring 2,5-connected 3,4-hexyl-thiophene corners, were synthesized. Macrocycles 1 and 2 respectively 3 and 4 differ in the positions of the acetyl-protected sulfur anchoring groups, which impacts both, the
individual transport efficiency of their parallel electronic pathways and their overall molecular wire lengths. All macrocycles were synthesized based on a series of Sonogashira crosscoupling reactions. For 3 and 4, a 2-(4-pyridinyl)ethyl protecting
group for the sulfur atoms was successful, while for macrocycles 1 and 2 the more common tert-butyl protecting group did the job. To our delight, proof-of-concept charge transport studies conducted in an MCBJ setup demonstrated the expected trends regarding improved conductance intensities for the TMCs compared to the BMCs. Furthermore, the corresponding molecular plateaus from the breaking experiments were in the expected length range of the S-S distances for all compounds. ... mehrWe also found that the overall conductance seems to follow a
more complex transport mechanism than just the sum of contributions from both channels.