Kubo–Martin–Schwinger-gated imaginary-time reconstruction of time-resolved electronic circular dichroism in organic excitonic aggregates
Year: 2026
Type: article
Abstract: Time-resolved electronic circular dichroism (TR-ECD) and time-resolved circular dichroism (TRCD) probe chiral exciton dynamics prepared by an ultrafast pump and interrogated by a weak circular probe. The measured signal is a causal mixed electric-magnetic response, whereas imaginary-time methods require a sufficiently stationary reference. Here, we introduce a Kubo-Martin-Schwinger-gated criterion that determines, at each pump-probe delay, whether the selected TRCD-like response can be represented by a conditional one-exciton Gibbs ensemble or requires explicit real-time or Keldysh dynamics. The diagnostic combines a state-level distance from the conditional reference with an integrated spectral distance for the reciprocal E1-M1 response. We apply the protocol to three literature-constrained Frenkel-exciton models: a Ress-type squaraine-polymer squeezed helix, a cisoid indolenine squaraine B hexamer, and a helical perylene-bisimide stack. The results show that early nonthermal states are non-admissible, whereas intramanifold population relaxation and the decay of coherence memory can open a Matsubara-admissible delay window before complete excited-state recovery. The resulting gate identifies when imaginary-time methods can be used without imposing a stationary description on a genuinely nonequilibrium chiroptical response.
Source: The Journal of Chemical Physics
DOI: 10.1063/5.0344268
Authors: Christian Tantardini, Caterina Cocchi
Language: English
Subfield: Atomic and Molecular Physics, and Optics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W7148176378
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