Decoding Conductance Dispersion using Single-Molecule Raman Spectroscopy

Understanding the structural origins of conductance dispersion remains a central challenge in single-molecule electronics. Here, we correlate vibrational fingerprints with conductance fluctuations in 4,4'-biphenyldithiol (BPDT) junctions to decode the structural origins of the statistical dispersion found in one-dimensional (1D) conductance histograms. As the conductance decreases, the vibrational modes near 1600 cm-1 undergo a distinct sequence. First, a low-frequency peak appears in the high-conductance regime relating to configurations with an extended molecular backbone. Next, two clear Raman peaks can be observed in the vicinity of the conductance peak relating to the equilibrium configuration; and finally, only the high-frequency peak exists in the low-conductance regime relating to configurations with high torsional distortion. Density functional theory (DFT) calculations reproduce both the Raman shift changes and the transmission trends, confirming the assignments. Together, these results provide a statistical framework for decoding the molecular structural origins of conductance dispersion in single-molecule junctions.