Search results for "transient absorption"
showing 10 items of 15 documents
Dynamic Diglyme-Mediated Self-Assembly of Gold Nanoclusters
2015
We report the assembly of gold nanoclusters by the nonthiolate ligand diglyme into discrete and dynamic assemblies. To understand this surprising phenomenon, the assembly of Au20(SC2H4Ph)15-diglyme into Au20(SC2H4Ph)15-diglyme-Au20(SC2H4Ph)15 is explored in detail. The assembly is examined by high-angle annular dark field scanning transmission electron microscopy, size exclusion chromatography, mass spectrometry, IR spectroscopy, and calorimetry. We establish a dissociation constant for dimer to monomer conversion of 20.4 μM. Theoretical models validated by transient absorption spectroscopy predict a low-spin monomer and a high-spin dimer, with assembly enabled through weak diglyme oxygen-g…
Characterization of Locally Excited and Charge-Transfer States of the Anticancer Drug Lapatinib by Ultrafast Spectroscopy and Computational Studies
2020
[EN] Lapatinib (LAP) is an anticancer drug, which is metabolized to theN- and O-dealkylated products (N-LAP andO-LAP, respectively). In view of the photosensitizing potential of related drugs, a complete experimental and theoretical study has been performed on LAP,N-LAP andO-LAP, both in solution and upon complexation with human serum albumin (HSA). In organic solvents, coplanar locally excited (LE) emissive states are generated; they rapidly evolve towards twisted intramolecular charge-transfer (ICT) states. By contrast, within HSA only LE states are detected. Accordingly, femtosecond transient absorption reveals a very fast switching (ca. 2 ps) from LE (lambda(max)=550 nm) to ICT states (…
In situobservation of the generation and annealing kinetics of E ′ centres induced in amorphous SiO2by 4.7 eV laser irradiation
2011
The kinetics of E' centers induced in silica by 4.7eV laser irradiation was investigated observing in situ their optical absorption band at 5.8 eV. After exposure the defects decay due to reaction with diffusing molecular hydrogen of radiolytic origin. Hydrogen-related annealing is active also during exposure and competes with the photo-induced generation of the centers until a saturation is reached. The concentrations of E' and H2 at saturation are proportional, so indicating that the UV-induced generation processes of the two species are correlated. These results are consistent with a model in which E' and hydrogen are generated from a common precursor Si-H.
Transient absorption with a femtosecond tunable excitation pump reveals the emission kinetics of color centers in amorphous silica.
2021
We report a set of femtosecond (fs) transient absorption (TA) measurements following the dynamics of the so-called nonbridging oxygen hole center in silica, a model color center in wide bandgap amorphous solids, characterized by a very large Stokes shift between the UV excitation and its associated red emission at 1.9 eV. The changes in the TA spectrum were probed in the UV-visible range at various delays after photoexcitation and analyzed as a function of the UV excitation energy, in single-photon absorption conditions. The combination of the experiments helps to clarify the defect photocycle, highlighting how TA measurements with tunable UV excitation could represent a powerful tool to in…
Simultaneous photonic and excitonic coupling in spherical quantum dot supercrystals
2020
Semiconductor nanocrystals, or quantum dots (QDs), simultaneously benefit from inexpensive low-temperature solution processing and exciting photophysics, making them the ideal candidates for next-generation solar cells and photodetectors. While the working principles of these devices rely on light absorption, QDs intrinsically belong to the Rayleigh regime and display optical behavior limited to electric dipole resonances, resulting in low absorption efficiencies. Increasing the absorption efficiency of QDs, together with their electronic and excitonic coupling to enhance charge carrier mobility, is therefore of critical importance to enable practical applications. Here, we demonstrate a ge…
Ab Initio Simulation of Attosecond Transient Absorption Spectroscopy in Two-Dimensional Materials
2018
We extend the first-principles analysis of attosecond transient absorption spectroscopy to two-dimensional materials. As an example of two-dimensional materials, we apply the analysis to monolayer hexagonal boron nitride (h-BN) and compute its transient optical properties under intense few-cycle infrared laser pulses. Nonadiabatic features are observed in the computed transient absorption spectra. To elucidate the microscopic origin of these features, we analyze the electronic structure of h-BN with density functional theory and investigate the dynamics of specific energy bands with a simple two-band model. Finally, we find that laser-induced intraband transitions play a significant role in…
Heptagon-Containing Nanographene Embedded into [10]Cycloparaphenylene
2023
We report the synthesis and characterization of a novel type of nanohoop, consisting of a cycloparaphenylene derivative incorporating a curved heptagon-containing π-extended polycyclic aromatic hydrocarbon (PAH) unit. We demonstrate that this new macrocycle behaves as a supramolecular receptor of curved π-systems such as fullerenes C60 and C70, with remarkably large binding constants (ca. 107 M−1), as estimated by fluorescence measurements. Nanosecond and femtosecond spectroscopic analysis show that these host-guest complexes are capable of quasi-instantaneous charge separation upon photoexcitation, due to the ultrafast charge transfer from the macrocycle to the complexed fullerene. These r…
Effect of Halogen Ions on the Photocycle of Fluorescent Carbon Nanodots
2019
Carbon dots (C-dots) are well-known for their strong sensitivity to the environment, which reflects on intensity and shape changes of their fluorescence, induced by various interacting ions and molecules in solution. Although these interactions have been extensively studied in the last few years, especially in view of their possible sensing applications, the existing works have mostly focused on the quenching of C-dot fluorescence induced by metal cations. In fact, these latter easily bind to C-dots surfaces, which are negatively charged in most cases, promoting an electron transfer from the surface to them. Much less is known from the literature on the effect induced on C-dots by prototypi…
Fast Photochemistry of Prototypical Phytochromes—A Species vs. Subunit Specific Comparison
2015
Phytochromes are multi-domain red light photosensor proteins, which convert red light photons to biological activity utilizing the multitude of structural and chemical reactions. The steady increase in structural information obtained from various bacteriophytochromes has increased understanding about the functional mechanism of the photochemical processes of the phytochromes. Furthermore, a number of spectroscopic studies have revealed kinetic information about the light-induced reactions. The spectroscopic changes are, however, challenging to connect with the structural changes of the chromophore and the protein environment, as the excited state properties of the chromophores are very sens…
Photodynamics of a Molecular Water-Soluble Nanocluster Identified as Au130(pMBA)50
2015
Photodynamics of a highly monodisperse sample of a water-soluble gold nanocluster tentatively identified as Au130(pMBA)50 (pMBA = p-mercaptobenzoic acid) was studied by mid-IR transient absorption spectroscopy with visible excitation. The observed long-lived excited states (>1 ns) indicate a molecular behavior of the cluster. By combining the transient absorption data with DFT calculation results the observed relaxation dynamics could be fully explained by identifying several relaxation processes involving singlet and triplet manifolds. The results indicate that the cluster may have interesting transient magnetic properties due to a long-lived triplet population.