Estimation of damped oscillation associated spectra from ultrafast transient absorption spectra

Abstract

When exciting a complex molecular system with a short optical pulse, all chromophores present in the system can be excited. The resulting superposition of electronically and vibrationally excited states evolves in time, which is monitored with transient absorption spectroscopy. We present a methodology to resolve simultaneously the contributions of the different electronically and vibrationally excited states from the complete data. The evolution of the excited states is described with a superposition of damped oscillations. The amplitude of a damped oscillation cos(ωnt)exp(−γnt) as a function of the detection wavelength constitutes a damped oscillation associated spectrum DOASn(λ) with an accompanying phase characteristic φn(λ). In a case study, the cryptophyte photosynthetic antenna complex PC612 which contains eight bilin chromophores was excited by a broadband optical pulse. Difference absorption spectra from 525 to 715 nm were measured until 1 ns. The population dynamics is described by four lifetimes, with interchromophore equilibration in 0.8 and 7.5 ps. We have resolved 24 DOAS with frequencies between 130 and 1649 cm−1 and with damping rates between 0.9 and 12 ps−1. In addition, 11 more DOAS with faster damping rates were necessary to describe the “coherent artefact.” The DOAS contains both ground and excited state features. Their interpretation is aided by DOAS analysis of simulated transient absorption signals resulting from stimulated emission and ground state bleach.

A Unified Experimental/Theoretical Description of the Ultrafast Photophysics of Single and Double Thionated Uracils

“…24TU samples were pumped at 330 and 270 nm, whereas 2TU was pumped at 270 nm (see Figure ). To describe the spectral evolution, we used global and target analyses with a sequential kinetic model . We also measured steady‐state photoluminescence (PL) at the same pump wavelengths.…”

A functional compartmental model of the Synechocystis PCC 6803 phycobilisome

“…The time-resolved spectra are described by a parameterized superposition model: where the populations are determined by an unknown compartmental model that depends upon the unknown kinetic parameters . In the target analysis, constraints on the SADS are needed to estimate all parameters and In order to also describe the vibrational evolution and the coherent artefact we add a superposition of damped oscillations (van Stokkum et al 2016 ). The amplitude of a damped oscillation as a function of the detection wavelength constitutes a damped oscillation-associated spectrum with an accompanying phase characteristic .…”

“…The interrelation between the DADS and SADS is expressed in the following matrix equation: Here the matrix contains in its l -th column the decay and the matrix contains in its columns the populations of the general compartmental model. The estimation of the DOAS is detailed in (van Stokkum et al 2016 ). When the compartmental model consists of a sequential scheme with increasing lifetimes the spectra are termed (evolution-associated difference spectra).…”

Exciton Transport in Molecular Aggregates – From Natural Antennas to Synthetic Chromophore Systems

“…Global analysis for cases including coherently oscillating signals (due to wavepacket dynamics) has also been developed recently. [68,69] It is in general not unique, [70] however, to decompose transient absorption data into in-time-evolving spectral components of individual intermediate species. Thus it is challenging to assign any recovered rates to particular microscopic processes.…”