Torsional Structural Relaxation Caused by Pt-Pt Bond Formation in the Photoexcited Dimer of Pt(II) N ̂ C ̂ N Complex in Solution.

[Pt(NCN)MeCN] (NCN = 1,3-di(2-pyridyl)benzene, MeCN = acetonitrile) forms oligomers in the ground state due to metallophilic interactions, and a Pt-Pt bond is formed with photoexcitation. Ultrafast excited-state dynamics of the [Pt(NCN)MeCN] dimer in acetonitrile is investigated by femtosecond time-resolved absorption (TA) and picosecond emission spectroscopy. The femtosecond TA signals exhibit 60 cm oscillations arising from the Pt-Pt stretching motion in the S dimer.

Quantifying Microsecond Solution-Phase Conformational Dynamics of a DNA Hairpin at the Single-Molecule Level.

Quantifying the rapid conformational dynamics of biological systems is fundamental to understanding the mechanism. However, biomolecules are complex, often containing static and dynamic heterogeneity, thus motivating the use of single-molecule methods, particularly those that can operate in solution. In this study, we measure microsecond conformational dynamics of solution-phase DNA hairpins at the single-molecule level using an anti-Brownian electrokinetic (ABEL) trap.

Pulsed-Interleaved-Excitation Two-Dimensional Fluorescence Lifetime Correlation Spectroscopy.

We report on pulsed-interleaved-excitation two-dimensional fluorescence lifetime correlation spectroscopy (PIE 2D FLCS) to study biomolecular structural dynamics with high sensitivity and high time resolution using Förster resonance energy transfer (FRET). PIE 2D FLCS is an extension of 2D FLCS, which is a unique single-molecule fluorescence method that uses fluorescence lifetime information to distinguish different fluorescence species in equilibrium and resolves their interconversion dynamics with a submicrosecond time resolution. Because 2D FLCS has used only a single-color excitation so far, it was difficult to distinguish a very low-FRET (or zero-FRET) species from only donor-labeled species.

Unified picture of vibrational relaxation of OH stretch at the air/water interface.

The elucidation of the energy dissipation process is crucial for understanding various phenomena occurring in nature. Yet, the vibrational relaxation and its timescale at the water interface, where the hydrogen-bonding network is truncated, are not well understood and are still under debate. In the present study, we focus on the OH stretch of interfacial water at the air/water interface and investigate its vibrational relaxation by femtosecond time-resolved, heterodyne-detected vibrational sum-frequency generation (TR-HD-VSFG) spectroscopy.

Ultrafast Raman observation of the perpendicular intermediate phantom state of stilbene photoisomerization.

Trans-cis photoisomerization is generally described by a model in which the reaction proceeds via a common intermediate having a perpendicular conformation around the rotating bond, irrespective of from which isomer the reaction starts. Nevertheless, such an intermediate has yet to be identified unambiguously, and it is often called the 'phantom' state. Here we present the structural identification of the common, perpendicular intermediate of stilbene photoisomerization using ultrafast Raman spectroscopy.

Complex phase of the nonresonant background in sum frequency generation spectroscopy.

Sum frequency generation (SFG) spectroscopy is an interface-selective spectroscopic technique that enables us to selectively observe the vibrational or electronic resonances of molecules within a very thin interface layer. The interfacial properties probed by SFG are contained in a complex quantity called the second-order nonlinear susceptibility (χ2). It is usually believed that the imaginary part of χ2 (Im χ2) exhibits the resonant responses of the system, whereas the nonresonant responses appear solely in the real part of χ2 (Re χ2).

Ultrafast vibrational control of organohalide perovskite optoelectronic devices using vibrationally promoted electronic resonance.

Vibrational control (VC) of photochemistry through the optical stimulation of structural dynamics is a nascent concept only recently demonstrated for model molecules in solution. Extending VC to state-of-the-art materials may lead to new applications and improved performance for optoelectronic devices. Metal halide perovskites are promising targets for VC due to their mechanical softness and the rich array of vibrational motions of both their inorganic and organic sublattices.

Effects of the Unique Chromophore-Protein Interactions on the Primary Photoreaction of Schizorhodopsin.

Schizorhodopsin (SzR) is a newly discovered microbial rhodopsin subfamily, functioning as an unusual inward-proton (H) pump upon absorbing light. Two major protein structural differences around the chromophore have been found, resulting in unique chromophore-protein interactions that may be responsible for its unusual function. Therefore, it is important to elucidate how such a difference affects the primary photoreaction dynamics.

Local pH at Nonionic and Zwitterionic Lipid/Water Interfaces Revealed by Heterodyne-Detected Electronic Sum-Frequency Generation: A Unified View to Predict Interfacial pH of Biomembranes.

For biomembranes, which are composed of neutral as well as charged lipids, the local pH at lipid/water interfaces is extremely important in their structural formation and functional activity. In our previous study of the charged lipid/water interfaces, we found that the local pH at the interface is governed by the positive or negative sign of the charge of the lipid: i.e.

Elucidation of the pH-Dependent Electric Double Layer Structure at the Silica/Water Interface Using Heterodyne-Detected Vibrational Sum Frequency Generation Spectroscopy.

The silica/water interface is one of the most abundant charged interfaces in natural environments, and the elucidation of the water structure at the silica/water interface is essential. In the present study, we measured the interface-selective vibrational (χ) spectra in the OH stretch region of the silica/water interface in a wide pH range of pH 2.0-12.

Photoexcited Plasmon-Driven Ultrafast Dynamics of the Adsorbate Probed by Femtosecond Time-Resolved Surface-Enhanced Time-Domain Raman Spectroscopy.

Metal nanoparticles have high potential in light-harvesting applications by transferring absorbed photon energy to the adsorbates. However, photoexcited plasmon-driven ultrafast dynamics of the adsorbate on metal nanoparticles have not been clearly understood. We studied ultrafast plasmon-driven processes of trans-1,2-bis(4-pyridyl)ethylene (BPE) adsorbed on gold nanoparticle assemblies (GNAs) using time-resolved surface-enhanced impulsive stimulated Raman spectroscopy (TR-SE-ISRS).

Single-photon smFRET. III. Application to pulsed illumination.

Förster resonance energy transfer (FRET) using pulsed illumination has been pivotal in leveraging lifetime information in FRET analysis. However, there remain major challenges in quantitative single-photon, single-molecule FRET (smFRET) data analysis under pulsed illumination including 1) simultaneously deducing kinetics and number of system states; 2) providing uncertainties over estimates, particularly uncertainty over the number of system states; and 3) taking into account detector noise sources such as cross talk and the instrument response function contributing to uncertainty; in addition to 4) other experimental noise sources such as background. Here, we implement the Bayesian nonparametric framework described in the first companion article that addresses all aforementioned issues in smFRET data analysis specialized for the case of pulsed illumination.

Spectroscopic mapping of the gold complex oligomers (dimer, trimer, tetramer, and pentamer) by excited-state coherent nuclear wavepacket motion in aqueous solutions.

We investigate the excited-state dynamics of the [Au(CN)] oligomers following photo-initiated intermolecular Au-Au bond formation by carrying out femtosecond time-resolved absorption and emission measurements at various concentrations (0.080-0.6 mol dm) with different photoexcitation wavelengths (290-340 nm).

Diamond-rich crystalline nanosheets seeded with a Langmuir monolayer of arachidic acid on water.

The enigmatic self-assembling ability of nanodiamond (ND) particles has been discovered herein. Diamond-rich crystalline nanosheets with thickness of approximately ∼25 nm were grown from a Langmuir monolayer of arachidic acid (AA) at the interface between air and a dilute aqueous ND solution. Their fine rectangular shapes with uniform uniaxial birefringence indicate appreciable crystallinity, thus supporting that they are hydrated colloidal crystals of homogeneous ND particles.

Attosecond electron-beam technology: a review of recent progress.

Electron microscopy and diffraction with ultrashort pulsed electron beams are capable of imaging transient phenomena with the combined ultrafast temporal and atomic-scale spatial resolutions. The emerging field of optical electron beam control allowed the manipulation of relativistic and sub-relativistic electron beams at the level of optical cycles. Specifically, it enabled the generation of electron beams in the form of attosecond pulse trains and individual attosecond pulses.

Why the Photochemical Reaction of Phenol Becomes Ultrafast at the Air-Water Interface: The Effect of Surface Hydration.

Photochemical reactions at the air-water interface can show remarkably different rates from those in bulk water. The present study elucidates the reaction mechanism of phenol characteristic at the air-water interface by the combination of molecular dynamics simulation and quantum chemical calculations of the excited states. We found that incomplete hydrogen bonding to phenol at the air-water interface affects excited states associated with the conical intersection and significantly reduces the reaction barrier, resulting in the distinctively facilitated rate in comparison with the bulk phase.

Superresolution concentration measurement realized by sub-shot-noise absorption spectroscopy.

Absorption spectroscopy is one of the most widely used spectroscopic methods. The signal-to-noise ratio in conventional absorption spectroscopy is ultimately limited by the shot noise, which arises from the statistical property of the light used for the measurement. Here we show that the noise in absorption spectra can be suppressed below the shot-noise limit when entangled photon pairs are used for the light source.

Scanning Two-Dimensional Fluorescence Lifetime Correlation Spectroscopy: Conformational Dynamics of DNA Holliday Junction from Microsecond to Subsecond.

Single-molecule Förster resonance energy transfer (smFRET) is widely utilized to investigate the structural heterogeneity and dynamics of biomolecules. However, it has been difficult to simultaneously achieve a wide observation time window, a high structure resolution, and a high time resolution with the current smFRET methods. Herein, we introduce a new method utilizing two-dimensional fluorescence lifetime correlation spectroscopy (2D FLCS) and surface immobilization techniques.

DNA-Induced Reorganization of Water at Model Membrane Interfaces Investigated by Heterodyne-Detected Vibrational Sum Frequency Generation Spectroscopy.

Lipid-DNA complexes are important nonviral vectors to be used in gene therapy, which is one of the promising strategies for the cure of many diseases. Although interfacial water is expected to play a significant role in lipid-DNA complexation, a molecular-level understanding about the role of interfacial water in the DNA-lipid complexation is still sparse. In this study, the structure and orientation of water at cationic and zwitterionic lipid monolayer/water interfaces in the presence of DNA are studied by the use of interface-selective heterodyne-detected vibrational sum frequency generation (HD-VSFG) spectroscopy.

Ultrafast dynamics of an azobenzene-containing molecular shuttle based on a rotaxane.

An ultrafast spectroscopic study was carried out for a photoisomerizable, rotaxane-based molecular shuttle, in which photoisomerization of the azobenzene moiety of the thread-like guest drives a shuttling motion of a cyclodextrin host. Femtosecond upconversion and time-resolved absorption measurements revealed distinct S dynamics with time constants of 1.2 and 17 ps.

Femtosecond Time-Resolved Absorption Study of Signaling State of a BLUF Protein PixD from the Cyanobacterium : Hydrogen-Bond Rearrangement Completes during Forward Proton-Coupled Electron Transfer.

Femtosecond time-resolved absorption measurements were carried out for the dark and signaling states of a BLUF (Blue Light Using FAD) protein, PixD, from the cyanobacterium . When the dark state was excited, FAD semiquinone radical (FADH) was produced from the S state, and FADH led to the signaling state. On the other hand, photoexcitation of the signaling state generated FADH and FAD anion radical (FAD), and they decayed back to the original signaling state.

A Unified View on Varied Ultrafast Dynamics of the Primary Process in Microbial Rhodopsins.

All-trans to 13-cis photoisomerization of the protonated retinal Schiff base (PRSB) chromophore is the primary step that triggers various biological functions of microbial rhodopsins. While this ultrafast primary process has been extensively studied, it has been recognized that the relevant excited-state relaxation dynamics differ significantly from one rhodopsin to another. To elucidate the origin of the complicated ultrafast dynamics of the primary process in microbial rhodopsins, we studied the excited-state dynamics of proteorhodopsin, its D97N mutant, and bacteriorhodopsin by femtosecond time-resolved absorption (TA) spectroscopy in a wide pH range.

Injection-seeded terahertz-wave parametric generator with timing stabilized excitation for nondestructive testing applications.

An injection-seeded terahertz (THz)-wave parametric generator (is-TPG) with a footprint the size of an A3 paper is presented. We improved the measurement performance of the is-TPG source for nondestructive inspection applications. A high pulse repetition rate up to 70 kHz and a low pulse timing jitter of a few tens of picoseconds, which is approximately one ten-thousandth of the conventional is-TPG, were achieved.