Ultrafast Intramolecular Charge Transfer of Formyl Perylene Observed Using Femtosecond Transient Absorption Spectroscopy

The excited-state photophysics of formylperylene (FPe) have been investigated in a series of nonpolar, polar aprotic, and polar protic solvents. A variety of experimental and theoretical methods were employed including femtosecond transient absorption (fs-TA) spectroscopy with 130 fs temporal resolution. We report that the ultrafast intramolecular charge transfer from the perylene unit to the formyl (CHO) group can be facilitated drastically by hydrogen-bonding interactions between the carbonyl group oxygen of FPe and hydrogen-donating solvents in the electronically excited state. The excited-state absorption of FPe in methanol (MeOH) is close to the reported perylene radical cation produced by bimolecular quenching by an electron acceptor. This is a strong indication for a substantial charge transfer in the S1 state in protic solvents. The larger increase of the dipole moment change in the protic solvents than that in aprotic ones strongly supports this observation. Relaxation mechanisms including vibrational cooling and solvation coupled to the charge-transfer state are also discussed

Heating and Cooling Dynamics of Carbon Nanotubes Observed by Temperature-Jump Spectroscopy and Electron Microscopy

Microscopy imaging indicates that in situ carbon nanotubes (CNTs) irradiation with relatively low dosages of infrared radiation results in significant heating of the tubes to temperatures above 1300 K. Ultrafast temperature-jump experiments reveal that CNTs laser-induced heating and subsequent cooling in solution take tens and hundreds of picoseconds, respectively. Given the reported transient behavior, these observations suggest novel ways for a T-jump methodology, unhindered by the requirement for excitation of water in the study of biological structures. They also provide the rate information needed for optimization of photothermal therapy that invokes infrared irradiation to selectively heat and annihilate cancer cells

Scanning ultrafast electron microscopy

Progress has been made in the development of four-dimensional ultrafast electron microscopy, which enables space-time imaging of structural dynamics in the condensed phase. In ultrafast electron microscopy, the electrons are accelerated, typically to 200 keV, and the microscope operates in the transmission mode. Here, we report the development of scanning ultrafast electron microscopy using a field-emission-source configuration. Scanning of pulses is made in the single-electron mode, for which the pulse contains at most one or a few electrons, thus achieving imaging without the space-charge effect between electrons, and still in ten(s) of seconds. For imaging, the secondary electrons from surface structures are detected, as demonstrated here for material surfaces and biological specimens. By recording backscattered electrons, diffraction patterns from single crystals were also obtained. Scanning pulsed-electron microscopy with the acquired spatiotemporal resolutions, and its efficient heat-dissipation feature, is now poised to provide in situ 4D imaging and with environmental capability

4D Scanning Ultrafast Electron Microscopy: Visualization of Materials Surface Dynamics

The continuous electron beam of conventional scanning electron microscopes (SEM) limits the temporal resolution required for the study of ultrafast dynamics of materials surfaces. Here, we report the development of scanning ultrafast electron microscopy (S-UEM) as a time-resolved method with resolutions in both space and time. The approach is demonstrated in the investigation of the dynamics of semiconducting and metallic materials visualized using secondary-electron images and backscattering electron diffraction patterns. For probing, the electron packet was photogenerated from the sharp field-emitter tip of the microscope with a very low number of electrons in order to suppress space–charge repulsion between electrons and reach the ultrashort temporal resolution, an improvement of orders of magnitude when compared to the traditional beam-blanking method. Moreover, the spatial resolution of SEM is maintained, thus enabling spatiotemporal visualization of surface dynamics following the initiation of change by femtosecond heating or excitation. We discuss capabilities and potential applications of S-UEM in materials and biological science

A comprehensive review on the exergy analysis of combined cycle power plants

The arriving optimum improvement of a thermodynamic system of energy conversion such as a combined cycle power plant (CCPP) is complicated due to the existence of different factors. Energy and exergy analysis is utilized as effective methods to determine both the quantity and quality of the energy sources. This paper reviews the latest thermodynamics analysis on each system components of a CCPP independently and determine the exergy destruction of the plant. A few layouts of the CCPP plant from different locations considered as case studies. In fact, the most energy losses occurred in the condenser compared with the plant components. It found that in the combustion chamber (CC) the highest exergy destruction occurred. The ambient temperature causes an evident decrement in the power production by the gas turbine (GT). The result has proved that besides energy, exergy analysis is an efficient way to the assessment of the performance of the CCPP by recommending a more advantageous configuration of the CCPP plant, which would lead to reductions in fuel required and emissions of air pollutants

Water-wire catalysis in photoinduced acid–base reactions

The pronounced ability of water to form a hyperdense hydrogen (H)-bond network among itself is at the heart of its exceptional properties. Due to the unique H-bonding capability and amphoteric nature, water is not only a passive medium, but also behaves as an active participant in many chemical and biological reactions. Here, we reveal the catalytic role of a short water wire, composed of two (or three) water molecules, in model aqueous acid–base reactions synthesizing 7-hydroxyquinoline derivatives. Utilizing femtosecond-resolved fluorescence spectroscopy, we tracked the trajectories of excited-state proton transfer and discovered that proton hopping along the water wire accomplishes the reaction more efficiently compared to the transfer occurring with bulk water clusters. Our finding suggests that the directionality of the proton movements along the charge-gradient H-bond network may be a key element for long-distance proton translocation in biological systems, as the H-bond networks wiring acidic and basic sites distal to each other can provide a shortcut for a proton in searching a global minimum on a complex energy landscape to its destination

(E)-1-(1,3-Benzodioxol-5-yl)-4,4-di­methyl­pent-1-en-3-one

In the mol­ecule of the title compound, C14H16O3, all non-H atoms except for one methyl C atom lie on a crystallographic mirror plane. The conformation with respect to the C=C bond [1.3465 (12) Å] is trans. In the crystal, mol­ecules are linked via C—H⋯O hydrogen bonds into C(5) chains propagating along [100]

Primary Peptide Folding Dynamics Observed with Ultrafast Temperature Jump

An ultrafast laser temperature jump (T-jump) induces folding and unfolding of Wh5 (see picture), the shortest possible α-helical peptide. Using time-resolved fluorescence spectroscopy, the folding time of this peptide was found to span from less than one nanosecond to a few nanoseconds, redefining the meaning of ultrafast dynamics in protein and peptide folding