Vibrational Energy Flow between Modes by Dynamic Mode Coupling in THIATS J-Aggregates

Abstract

We performed ultrafast pump-probe spectroscopy of J-aggregates of 3,3'-disulfopropyl-5,5'-dichloro-9-ethyl thiacarbocyanine triethylammonium (THIATS), one of the most typical cyanine dyes, and detected excited molecular vibrations, using a sub-10 fs pulse laser. The time-resolved two-dimensional difference absorption (ΔA) spectra are observed between -314 and 1267 fs. By performing the Fourier transform and spectrogram analysis, vibrational modes in THIATS are observed at 285, 485, 555, 824, and 1633 cm(-1) and there was a modulation of the vibrational frequencies around 1633 cm(-1) which depend on the delay time, respectively. By the analysis of the modulation, energy flow is found to take place from other modes to the 1633 cm(-1) mode through the low frequency mode with ∼50 cm(-1). Also, by fitting the real-time traces of ΔA with the sum of two exponential functions and a constant term, the average lifetimes of three electronically excited states were found to be τ1 = 52 ± 5 fs and τ2 = 540 ± 78 fs. By performing single-exponential fitting around the stationary absorption peak at 1.990 eV, in the negative time range, the electronic dephasing time, T2(ele), is determined to be 18.30 fs.

Time-frequency methods for coherent spectroscopy

“…Indeed, apart from the pioneering works of T. Kobayashi and A. Stolow, who have demonstrated TFTs in analyzing wavepacket dynamics in ultrafast pump-probe signals, few are the examples of TFT analysis applied to spectroscopic signals. In particular the sliding-window Fourier Transform (or short-time Fourier transform as defined in Section 3.1) was successfully applied, for example, toward analysis of complex wavepacket dynamics in the gas-phase [19], dynamical mode coupling and mode-mixing [20,21], and real-time reaction dynamics in the condensed phase [22,23].…”

Principles for Self-Assembly of Cyanine Dyes into 2-Dimensional Excitonic Aggregates Across the Visible and Near-Infrared

“…Cy1, 17 Cy3, 18,19 , THIATS, 20 Cy5, 21 Cy7 22 Langmuir-Blodgett films Cy1 23,24 Adsorption on a surface Cy1, 25 Cy3 26,27 , THIATS 28 Thin films THIATS, 29,30 Cy3, 31,32 Cy7 33 Crystallization on interface Cy3 34 DNA or polymer templating Cy1, 35 Cy3, 36 Cy5, 36,37 of the aggregate structure itself and thus provide a platform for chemical control of excitonic properties. 7,38 However, achieving control over aggregate structure requires chemical/physical control over the aggregation process.…”

“…Cy3-Et is structurally related to the commonly studied THIATS chromophore, differing only in the number of carbons (3 vs 4) in the sulfoalkyl chain. 29 Several strategies have been used to aggregate THIATS and other benzothiazole cyanine dyes, summarized in the Table 1, including direct dissolution in water, 22 adsorption of silver halide surface, 26 and spin coating. 29 Here, we stabilize Cy3-Et aggregates under a variety of conditions by independent control of different solvation conditions.…”

“…29 Several strategies have been used to aggregate THIATS and other benzothiazole cyanine dyes, summarized in the Table 1, including direct dissolution in water, 22 adsorption of silver halide surface, 26 and spin coating. 29 Here, we stabilize Cy3-Et aggregates under a variety of conditions by independent control of different solvation conditions. First, we make a monomer solution of the dye in methanol and disperse it into an aqueous solution (with or without NaCl), a more generalized modification of the wellknown 'alcoholic route'.…”

Optimization and selection of time-frequency transforms for wave-packet analysis in ultrafast spectroscopy

“…Whatever the nature of the studied material or the particular technique and time resolution used, the analysis of the frequency and time behavior of the beatings is a key ingredient to extract information about the system dynamics. To this aim, methodologies based on linear and bilinear time-frequency transforms (TFT) have been already proposed and applied to ultrafast 1D [14][15][16][17][18][19] and 2D spectroscopy measurements [20][21][22][23][24][25][26]. The advantage of TFTs is that they analyze a non-stationary oscillating signal providing both time and frequency resolution, spreading out the information content along the two dimensions of the time-frequency plane [27].…”