Carbon nanotubes (CNTs) are appealing candidates for solar and optoelectronic applications. Traditionally used as electron sinks, CNTs can also perform as electron donors, as exemplified by coupling with perylenediimide (PDI). To achieve high efficiencies, electron transfer (ET) should be fast, while subsequent charge recombination should be slow. Typically, defects are considered detrimental to material performance because they accelerate charge and energy losses. We demonstrate that, surprisingly, common CNT defects improve rather than deteriorate the performance. CNTs and other low dimensional materials accommodate moderate defects without creating deep traps. At the same time, charge redistribution caused by CNT defects creates an additional electrostatic potential that increases the CNT work function and lowers CNT energy levels relative to those of the acceptor species. Hence, the energy gap for the ET is decreased, while the gap for the charge recombination is increased. The effect is particularly important because charge acceptors tend to bind near defects due to enhanced chemical interactions. The time-domain simulation of the excited-state dynamics provides an atomistic picture of the observed phenomenon and characterizes in detail the electronic states, vibrational motions, inelastic and elastic electron–phonon interactions, and time scales of the charge separation and recombination processes. The findings should apply generally to low-dimensional materials, because they dissipate defect strain better than bulk semiconductors. Our calculations reveal that CNT performance is robust to common defects and that moderate defects are essential rather than detrimental for CNT application in energy, electronics, and related fields.

Colloidal CdSe nanocrystals are often stabilized by organic ligands. The choice of such ligands has tremendous detrimental effects on interparticle charge transfer (CT) dynamics in nanocrystalline thin-film devices. It is evident from the recent experiment that photoexcited hole migrates from CdSe quantum dot (QD) to surface-passivating phenyl chalcogenol ligands (PhEH; E = S, Se, Te) at different time scales. But the backward electron−hole (e−h) recombination at the interface remained unexplored. A deep-level understanding of the mechanism of CT at the interface is therefore required to unravel the key role of chalcogen for the betterment of the device performance. Herein, we have performed timedomain density functional theory calculation along with nonadiabatic molecular dynamics (NAMD) simulation to investigate the photoinduced CT at the CdSe−PhEH interfaces. The simulated time scales for hole transfer (HT) are found to follow the trend PhSH > PhSeH > PhTeH that concur excellently with the experimental observations. We propose that lower electronegativity of the E atom that binds with the CdSe QD facilitates the hole migration. In addition, the delocalized nature of initial donor states, phonon modes, NA coupling, and quantum coherence are the major factors that control the faster HT. Meanwhile, for the first time, we study the linker atom-dependent e−h recombination at such interface. The recombination event is remarkably slower than the HT and occurs at the nanosecond regime. Due to the greater electronegativity of linker atom (E = S), a broad range of phonon vibration and longer-lived quantum coherence expedite the recombination at a higher rate. In contrast, for higher chalcogens with lower electronegativity (Se, Te), the exciton relaxes relatively at a lower rate. We believe our results of atomistic, time-domain methodology provide valuable insight into the exciton relaxation dynamics in CdSe−chalcogenol interface and may be useful for the enhancement of performance of future devices.

The versatile photochemical properties of porphyrin molecules make them excellent candidates for solar energy applications. Carbon nanotubes (CNTs) exhibit superior charge conductivity and have been combined with porphyrins to achieve efficient and ultrafast charge separation. Experiments show that the charge separated state lives less than 10 ps, which is too short for applications. Using real-time time-dependent tight binding density functional theory (DFTB) combined with non-adiabatic molecular dynamics (NAMD), we model photo-induced charge separation and recombination in two porphyrin/CNT composites. Having achieved excellent agreement with the experiment for the electron transfer from the porphyrins to the CNT, we demonstrate that hole transfer can be achieved upon CNT excitation, although in a less efficient way. By exciting the CNT one can extend light harvesting into lower energies of the solar spectrum and increase solar light conversion efficiency. We also show that the charge separated state can live over 1 ns. The two orders of magnitude difference from the experimental lifetime could arise due to the presence of defects or metallic tubes in the samples. The charge separated state is long-lived because the non-adiabatic electron-phonon coupling is very small, less than 1 meV, and the quantum coherence is short, 15-20 fs. The excited states in the isolated porphyrins and CNT live around 100 ps, in agreement with experiments as well. The porphyrin/CNT interaction occurs through the π-electron systems of the two species. The non-radiative relaxation is promoted by both high and low frequency phonons, with higher frequency phonons playing more important roles in electron relaxation than in hole relaxation. Low frequency phonons contribute significantly to the decay of the charge separated state, because they modulate the relative positions of the porphyrins and the CNT. The time-domain atomistic simulations provide a detailed understanding of the charge separation and recombination mechanisms, and generate valuable guidelines for the optimization of photovoltaic efficiency in modern nanoscale materials.

Structural rigidity assists to weaken the NA electron–phonon coupling, shorten the quantum coherence and thus suppress the dynamics of electron–hole recombination.

Saddle-shaped zinc porphyrin nanorings are utilized as light-harvesting materials. To achieve high performance, both fast charge transfer and slow charge recombination are required. Fast transfer favors efficient separation of exciton into free carriers, enhancing photocurrent. Slow recombination reduces charge and energy losses. We simulated both processes using time-dependent self-consistent-charge density functional tight binding theory combined with nonadiabatic (NA) molecular dynamics. The obtained picosecond charge recombination times agree well with experiment. The simulations demonstrate that the carrier lifetime depends strongly on the metals present in the porphyrin nanoring. When the porphyrin units are composed of Zn centers only, the simulated lifetime is 55 ps. If nanorings contain both Zn and Cd, the nonradiative recombination is suppressed to 200 ps, nearly 4 times. Incorporation of Cd partially localizes the photogenerated charges, weakens the NA coupling, and accelerates phonon-induced loss of electronic coherence. The heavier and slower Cd also decreases the NA coupling. The nonradiative recombination is driven by low-frequency phonons, with a moderate contribution from the C–C stretch. Our study demonstrates a straightforward pathway to reducing charge losses in the porphyrin nanorings by partial exchange of Zn atoms with Cd and provides a valuable guideline for improvement of the material efficiency for solar energy applications.

The systematic screening for p53 mutations in European patients with hilar cholangiocarcinoma has shown that the type of mutation (except 175) is different and its incidence is much lower when compared to the pattern previously reported for intrahepatic cholangiocarcinoma in East Asian patients. A probable explanation is that the presence and type of p53 mutation is dependent on geographic and environmental factors which vary in different populations.

This study describes comparative occurrence and characterization of multidrug-resistant (MDR) Escherichia coli and Klebsiella pneumoniae (KP) in healthy cattle (HC) and cattle with diarrhea (DC) in India.

Coinage metal hydride anions, especially AgH−, can effectively and deterministically hydrogenate CO2 to HCO2−.