Broadband Transient Absorption and Two-Dimensional Electronic Spectroscopy of Methylene Blue

Abstract

Broadband transient absorption and two-dimensional electronic spectroscopy (2DES) studies of methylene blue in aqueous solution are reported. By isolating the coherent oscillations of the nonlinear signal amplitude and Fourier transforming with respect to the population time, we analyzed a significant number of coherences in the frequency domain and compared them with predictions of the vibronic spectrum from density function theory (DFT) calculations. We show here that such a comparison enables reliable assignments of vibrational coherences to particular vibrational modes, with their constituent combination bands and overtones also being identified via Franck–Condon analysis aided by DFT. Evaluation of the Fourier transform (FT) spectrum of transient absorption recorded to picosecond population times, in coincidence with 2D oscillation maps that disperse the FT spectrum into the additional excitation axis, is shown to be a complementary approach toward detailed coherence determination. Using the Franck–Condon overlap integrals determined from DFT calculations, we modeled 2D oscillation maps up to two vibrational quanta in the ground and excited state (six-level model), showing agreement with experiment. This semiquantitative analysis is used to interpret the geometry change upon photoexcitation as an expansion of the central sulfur/nitrogen containing ring due to the increased antibonding character in the excited state.

On the Non‐Metallicity of 2.2 nm Au246(SR)80 Nanoclusters

“…Meanwhile, the amplitude also exhibits two local minima at the same region. The phase shift of oscillations typically occurs at the bottom of PES accompanied by the node of zero amplitude . As both the phase shift and amplitude node are found in the maxima of GSB, the oscillations observed here should arise from the wavepacket motion on the PES of the ground state rather than the excited state.…”

Estimation of damped oscillation associated spectra from ultrafast transient absorption spectra

“…Vibrations can be assigned to the ground or excited state based on their amplitude and phase profiles, where a node in the amplitude, accompanied by a corresponding phase flip, marks the minimum of the electronic potential energy surface that the wavepacket is propagating on. [5][6][7][25][26][27][28][29] Vibronic coherences are relevant to the study of photosynthetic energy transfer, 25,27,[30][31][32][33][34][35][36][37][38] photosynthetic charge separation, 39 exciton coherence, 40 electa) Electronic mail: i.h.m.van.stokkum@vu.nl. Telephone: +31205987868.…”

“…ron transfer, 28 internal conversion, 2 light-activated geometry changes, 5 conical intersections, 7 photoisomerization, 1,20,29,41 photodissociation, 42,43 and coherent phonons in polymers and crystals. [44][45][46] In order to investigate the dynamics revealed in transient absorption spectra, populations and oscillations are currently treated separately.…”

Cooperative Subunit Refolding of a Light‐Harvesting Protein through a Self‐Chaperone Mechanism

“…[19,20] In this way,c oherent electronic spectroscopy can be utilized for its inherent selectivity of the eight structurally distributed tetrapyrroles,thus exploiting them as local probes of the protein scaffold itself (Figure 2). Specifically,w e implemented broadband transient absorption (BBTA) spectroscopy,w here the coherent oscillations along the pumpprobe time delay are recorded as af unction of probe frequency (n 3 ), and two-dimensional electronic spectroscopy (2DES), [21] which further disperses the BBTAsignal into two dimensions by resolving the excitation axis (n 1 )inaddition to the detection axis (n 3 ). Thec ombination of the two methods allowed us to decisively compare coherences for the proteins on ultrafast (fs) to picosecond timescales.…”