Tuning macrocyclic thermoelectrics via thiophene regioisomerism

Quantum interference (QI) in single-molecule junctions exhibits robust effects at room temperature, which can be intuitively modeled using quantum circuit rules (QCR) and magic ratio (MR) theory. These frameworks describe how molecular conductance is governed by constituent moieties and their connectivity. Here, we apply these principles to explore the thermoelectric properties of a series of macrocyclic structures featuring multiple electron pathways, with mixed meta and para connectivities. Our density functional theory (DFT) calculations rationalize the experimentally measured conductance trends, demonstrating excellent agreement between theory and experiment. Furthermore, we predict that these macrocyclic junctions achieve significantly higher Seebeck coefficients than conventional single-branched analogues. A key finding is that strategic repositioning of sulfur atoms within the thiophene rings enables fine tuning of QI, modulating conductance and thermoelectric performance. Our work establishes macrocyclic architectures with tunable connectivities as a highly promising platform for advanced molecular thermoelectrics.