Scaling Diradicaloid Thermoelectricity

The identification of molecular materials with high thermoelectric performance has attracted considerable attention due to their unique quantum properties, elemental abundance, and environmental friendliness. Achieving this requires overcoming the conventional tradeoff between the Seebeck coefficient (S) and electrical conductance (G). Here, we exploit the thermoelectric properties of diradicaloid molecular junctions and demonstrate the coenhancement of G and S. Calculations predict that elongating the diradicaloid backbone systematically reduces the energy gap, pushing transport resonances closer to the electrode's Fermi energy, leading to the simultaneous improvement of G and S, and a length-dependent increase in power factor unlike that of conventional conjugated molecules. This is confirmed in self-assembled monolayers (SAMs) formed from diradicaloids, where we observe an increase in G with the diradicaloid length and S reaching values exceeding 40 μV/K. This shows exotic quantum transport properties of single-molecule diradicaloids translate to technologically relevant SAMs for next-generation high-performance thermoelectric energy conversion devices.