Ultrafast two-dimensional infrared spectroscopy for molecular structures and dynamics with expanding wavelength range and increasing sensitivities: from experimental and computational perspectives

Ultrafast Intermolecular Vibrational Energy Transfer in Hexahydro-1,3,5-trinitro-1,3,5-triazine in Molecular Crystal by 2D IR Spectroscopy

“…These works demonstrated the power of the infrared methods in studying such energetic materials, particularly the 2D IR method, which is essentially a coherent and multidimensional pump–probe IR method possessing both high time resolution and high structural sensitivity and can simultaneously excite and probe many vibrational chromophores with varying frequencies in the mid-IR region . For this reason, in recent years, the 2D IR method has attracted extensive attention in the study of the structures and dynamics of condensed-phase molecular systems, as well as interface and surface molecular systems. − …”

Intensified C≡C Stretching Vibrator and Its Potential Role in Monitoring Ultrafast Energy Transfer in 2D Carbon Material by Nonlinear Vibrational Spectroscopy

“…In this work, the vibrational properties of the CC bond in hexakis­[(trimethylsilyl)­ethynyl] benzene (HTEB, Figure a Insert), which has been used to synthesize hexaethynylbenzene, a precursor of graphdiyne, is examined using both the conventional IR, time-resolved infrared method and the femtosecond two-dimensional infrared (2D IR) method. − In recent years, the 2D IR method has been used to unravel ultrafast structural dynamics in condensed-phase molecular systems, ,− as well as in surface-immobilized molecular systems. − The time-resolved IR method, on the other hand, can yield vibrational relaxation dynamics as well as anisotropy dynamics. − Particularly, in 2D IR spectroscopy, a collection of 2D joint distributions of frequency fluctuations is shown and vary with the dynamical time (or waiting time). In a 2D IR spectrum, one part of the diagonal signal is the ν = 0 → ν = 1 transition (ν is vibrational quantum number), reflecting the autocorrelation of this transition frequency distribution, while the other part of the diagonal signal is the ν = 1 → ν = 2 transition, reflecting the cross-correlation of the 0 → 1 and 1 → 2 transition-frequency distributions.…”

Ultrafast Structure and Vibrational Dynamics of a Cyano-Containing Non-Fullerene Acceptor for Organic Solar Cells Revealed by Two-Dimensional Infrared Spectroscopy

“…It also shows the as–as mode (Δ ss–as ≈ 8.6 cm –1 ), which appears due to ultrafast energy transfer (i.e., intramolecular vibrational energy redistribution, IVR) from the ss–as mode to the as–as mode in the form of off-diagonal signal, actually has the diagonal anharmonicity of the energy-accepting mode (as–as). Figure a also reveals another type of off-diagonal anharmonicity that is due to AVC , between the ss–as mode and as–as mode (Δ ss–as,as–as ≈ 22.8 cm –1 ), which differs from and is significantly larger than both of the diagonal anharmonicities. From Figure b, a similar set of diagonal and off-diagonal anharmonicities are obtained at 2.5 ps waiting time (Table ), justifying the fitting results obtained from Figure a.…”

“…23 Å in the ITIC system, as a result of efficient mechanical anharmonic coupling that is evidenced by substantially larger off-diagonal anharmonic coupling between the high-frequency ss–as mode and low-frequency as–as mode. It is the cubic and high-order force constants in the potential energy that determine these energy levels involved in the transitions, as shown in the 2D IR spectra . The structure basis for these vibrational and energetic features is the conjugating molecular frame that is composed of a network of double bonds, facilitating both vibrational and electron delocalizations.…”

“…Two-dimensional infrared (2D IR) spectroscopy is a very useful method for studying condensed-phase molecular structures, their structural distributions, and intra- and/or intermolecular vibrational energy redistribution or transfer (IVR and/or VET) processes with ultrafast time resolution. − Average structural details can be seen in the 2D line shape of the diagonal peaks that are directly associated with the molecular vibrations of interest, and additional structural geometry can be extracted from the pairwise off-diagonal 2D peaks due to anharmonic vibrational coupling (AVC). The structural dynamics, on the other hand, are seen in time-dependent 2D diagonal peaks in the form of spectral diffusion (SD), , for example.…”