Calculations of Nonlinear Wave-Packet Interferometry Signals in the Pump-Probe Limit as Tests for Vibrational Control over Electronic Excitation Transfer

TL;DR

This paper calculates nonlinear wave-packet interferometry signals in pump-probe experiments to test vibrational control over electronic excitation transfer in molecular dimers, demonstrating how vibrational modes influence EET dynamics.

Contribution

It introduces a method to compute pump-probe difference signals in nl-WPI, linking vibrational control strategies with spectroscopic detection of EET in complex molecular systems.

Findings

Calculated signals for a model excitation-transfer complex with intramolecular vibrations.

Demonstrated vibrational mode influence on EET dynamics in a covalent dimer model.

Showed how electronic-vibrational coupling affects the pump-probe signals.

Abstract

The preceding paper describes a strategy for externally influencing the course of short-time electronic excitation transfer (EET) in molecular dimers and observing the process by nonlinear wave-packet interferometry (nl-WPI). Within a sample of isotropically oriented dimers having a specified internal geometry, a vibrational mode internal to the acceptor chromophore can be preferentially driven by electronically nonresonant impulsive stimulated Raman (or resonant infrared) excitation with a short polarized control pulse. A subsequent electronically resonant polarized pump then preferentially excites the donor, and EET ensues. Here we test both the control strategy and its spectroscopic investigation-with some sacrifice of amplitude-level detail-by calculating the pump-probe difference signal. That signal is the limiting case of the control-influenced nl-WPI signal in which the two pulses in the pump pulse-pair coincide, as do the two pulses in the probe pulse-pair. We present calculated pump-probe difference signals for (1) a model excitation-transfer complex in which two equal-energy monomers each support one moderately Franck-Condon active intramolecular vibration; (2) a simplified model of the covalent dimer dithia-anthracenophane, representing its EET dynamics following selective impulsive excitation of the weakly Franck-Condon active anthracene vibration at 385 cm-1; and (3) a model complex featuring moderate electronic-vibrational coupling in which the site energy of the acceptor chromophore is lower than that of the donor.