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O: Fachverband Oberflächenphysik

O 12: Scanning probe microscopy: light matter interaction at atomic scales

O 12.11: Vortrag

Montag, 9. März 2026, 17:30–17:45, HSZ/0403

Orbital-resolved imaging of coherent femtosecond exciton dynamics in single molecules — •Caiyun Chen — Max Planck Institute for Solid State Research, Heisenbergstraße 1, 70569 Stuttgart

Understanding and controlling excitonic wavepackets is fundamental to uncovering mechanisms underlying energy conversion dynamics in organic molecular systems. We present orbital-resolved imaging of coherent exciton dynamics in single metal-centered naphthalocyanine (MNc) molecules*CoNc, CuNc, and ZnNc*adsorbed on NaCl/Ag(111). Using femtosecond scanning tunneling microscopy, we directly observe time-resolved photocurrent signals and spectroscopic signatures of coherent excitons, enabling selective excitation and control of excitons in isolated and coupled molecules. In single CuNc molecules, we measure a decoherence time (~70 fs), which decreases in dimers due to intermolecular interactions. Time-resolved measurements and photocurrent imaging reveal how central metal atoms in different naphthalocyanine molecules influence decoherence dynamics of the excited electronic state. Notably, a ZnNc molecule has longer decoherence time (~ 300 fs) compared to the CuNc and CoNc (~ 30 fs). Unpaired electrons on Co in CoNc molecule leads to distinct photocurrent imaging contrasts with the closed shell ZnNc and CuNc molecules. The origin of faster decoherence times of the excited states in CoNc and CuNc molecules is linked to conical intersections. These findings underscore the applications of ultrafast STM to probe quantum coherence and energy transfer dynamics at the single-molecule level with atomic-scale spatial resolution.

Keywords: Femtosecond Scanning Tunneling Microscopy (fs-STM); Quantum Coherence; Single Naphthalocyanine (MNc) Molecules; Ultrafast Dynamics