Two-Dimensional Electronic Spectroscopy of β-Carotene

Abstract

Two-dimensional electronic spectroscopy (2D) has been applied to beta-carotene in solution to shine new light on the ultrafast energy dissipation network in carotenoids. The ability of 2D to relieve spectral congestion provides new experimental grounds for resolving the rise of the excited state absorption signal between 18,000 and 19,000 cm(-1). In this spectral region, the pump-probe signals from ground state bleach and stimulated emission overlap strongly. Combined modeling of the time-evolution of 2D spectra as well as comparison to published pump-probe data allow us to draw conclusions on both the electronic structure of beta-carotene as well as the spectral densities giving rise to the observed optical lineshapes. To account for the experimental observations on all time scales, we need to include a transition in the visible spectral range from the first optically allowed excited state (S(2)-->S(n2)). We present data from frequency resolved transient grating and pump-probe experiments confirming the importance of this transition. Furthermore, we investigate the role and nature of the S* state, controversially debated in numerous previous studies. On the basis of the analysis of Feynman diagrams, we show that the properties of S*-related signals in chi(3) techniques like pump-probe and 2D can only be accounted for if S* is an excited electronic state. Against this background, we discuss a new interpretation of pump-deplete-probe and intensity-dependent pump-probe experiments.

Quantum Chemical Description of Absorption Properties and Excited‐State Processes in Photosynthetic Systems

“…[197] On the other hand, the data from two-dimensional electronic and pump-probe spectroscopy of the same carotenoid could only be consistently explained if the presence of an additional excited electronic state (S*) was assumed. [198] Similar conclusions were drawn from a femtosecond absorption and Kerr-gate fluorescence spectroscopy study on b-carotene homologues and lycopene. [188] Thus, the character of the S* state is still a matter of debate.…”

Ultra-broadband 2D electronic spectroscopy of carotenoid-bacteriochlorophyll interactions in the LH1 complex of a purple bacterium

“…[28][29][30][31][32] Due to its unique combination of spectral and temporal resolution, 2DES has been very recently used for studying the LH complexes of purple bacteria to unveil both the electronic structure and dynamics 21,[33][34][35][36][37][38][39] and to follow the IC dynamics of the isolated Cars. 20,40,41 So far two experimental approaches have been successfully used to implement 2DES: the non-collinear, heterodynedetected three-pulse photon echo 42,43 and the partially collinear pump-probe geometry. [44][45][46] Both approaches present advantages but also limitations and technical difficulties.…”

Ultrabroadband THz Time-Domain Spectroscopy of a Free-Flowing Water Film

“…However, a stable sub-20 m thick water film is rather difficult to produce, and most spectroscopic investigations based on this technique have been employing films with thicknesses in the 50-200 m range. Furthermore, the surface cross sectional shape of the water film has not been investigated in detail, in spite of its extensive use in ultrafast mid-infrared spectroscopic investigations [15]- [18]. Thus, the performance of such a thin water film and its influence on the beam path in a THz-TDS system needs to be characterized.…”