Time-resolved Studies Research Articles

Pushing the heterometal doping limit while preserving long-lived charge separation in a Ti-based MOF photocatalyst

This study explores the nature, dynamics, and reactivity of the photo-induced charge separated excited state in a Fe3+-doped titanium-based metal organic framework (MOF), xFeMIL125-NH2, as a function of iron concentration. The MOF is synthesized with doping levels x = 0.5, 1 and 2 Fe node sites per octameric Ti-oxo cluster and characterized by powder x-ray diffraction, UV-vis diffuse reflectance, atomic absorption, and steady state Fe K-edge X-ray absorption spectroscopy. For each doping level, time-resolved X-ray transient absorption spectroscopy studies confirm the electron trap site role of the Fe sites in the excited state. Time scan data reveal multiexponential decay kinetics for the charge recombination processes which extend into the microsecond range for all three concentrations. A series of dye photodegradation studies, based on the oxidative decomposition of Rhodamine B, demonstrates the reactivity of the charge separated excited state and the photocatalytic capacity of these MOF materials compared to traditional heterometal-doped semiconductor photocatalysts.

High time-resolved studies of stick-slip show similar dilatancy to fast and slow earthquakes.

Fast and slow earthquakes are two modes of energy release by the slip in tectonic fault rupture. Although fast and slow slips were observed in the laboratory stick-slip experiments, due to the sampling rate limitation, the details of the fault thickness variation were poorly understood. Especially, why a single fault would show different modes of slip remains elusive. Herein, we report on ring shear experiments with an ultrahigh sampling rate (10 MHz) that illuminate the different physical processes between fast and slow slip events. We show that the duration of slips ranged from dozens to hundreds of milliseconds. Fast slip events are characterized by continuous large-amplitude AE (acoustic emission) and somewhat intricate variation of the sample thickness: A short compaction pulse during the rapid release of stress is followed by dilation and vibrations of the sample thickness. As the slip ends, the thickness of the sample first recovers by slow compaction and then dilates again before nucleation of the following slip event. In contrast, during slow slip events, the shear stress reduction is accompanied by intermittent bursts of low-amplitude AE and sample dilation. We observed the detailed thickness variation during slips and found that dilation occurs during both fast and slow slips, which is consistent with natural observations of coseismic dilatation. This study may be used to reveal the mechanism of fault slips during fast and slow earthquakes, which explain the potential effect of fast and slow slips on stress redistribution and structural rearrangement in faults.

CuBO2 : A Potential Alternative for NiO as a Hole Acceptor Layer.

P-type metal oxides, and in particular NiO, are typically used as hole accepting layers in dye-sensitized photocathodes. Delafossites (CuMO2 ) with M=B, Al, Cr or Ga have recently been proposed as attractive substitutes for NiO, with theoretically a higher hole mobility than NiO, therefore allowing a higher efficiency when the photocathode is applied in solar to fuel devices. We have experimentally validated the photoelectrochemical performance of photocathodes consisting of nanoporous CuBO2 (CBO) on Fluorine-doped Tin Oxide substrates, photosensitized with a light absorbing P1 dye. Femtosecond transient absorption and time-resolved photoluminescence studies show that light-induced hole injection occurs from the P1 dye into the CBO in a few ps, comparable to the time constant observed for NiO-based photocathodes. Importantly, the CBO-based photocathode shows significantly slower charge recombination than the NiO-based analogue. These results illustrate the promise of CBO as a p-type semiconductor in solar energy conversion devices.

Molecular beam laser spectroscopic studies of the photoactive properties of resveratrol

Resonance Enhanced MultiPhoton Ionization spectroscopic techniques coupled with laser desorption and supersonic cooling have been employed to elucidate the photoactive properties of resveratrol. The observed excitation spectra give evidence for an internal-energy dependent trans–cis isomerisation pathway in the electronically excited state, while pump-probe studies show dynamics that are in line with what is known for the parent compound, trans-stilbene. Similar studies have been performed on a derivative of resveratrol with methoxy instead of hydroxy groups, a compound aimed to reduce previously observed photodegradation pathways of resveratrol. Time-resolved studies of the latter compound under solution conditions have given further insight into its excited-state dynamics and support the isolated-molecule conclusions on the topology of the potential energy surface of the electronically excited state. Spectroscopic studies under prolonged irradiation conditions show that both compounds suffer from photodegradation, although in the alkylated compound other pathways appear to be involved than in resveratrol.Graphical abstract

Evidence for an Interface of Hybrid Cocatalysts Favoring Photocatalytic Hydrogen Evolution Kinetics.

Hybrid cocatalysts have great application potential for improving the photocatalytic hydrogen evolution performance of semiconductors. The interfaces between components of hybrid cocatalysts make a great contribution to the improvement, but the associated mechanisms remain unclear. Herein, we prepared and tested three comparative CdS-based photocatalysts with NiS, NiS/Ni9S8, and Ni9S8 as the cocatalysts separately. The emphasis is placed on investigating the effect of the NiS/Ni9S8 interfaces on the photocatalytic hydrogen evolution performance of CdS. NiS/Ni9S8 exhibits a higher ability than NiS and Ni9S8 in making CdS a more active photocatalyst for water splitting. It shows that NiS, NiS/Ni9S8, and Ni9S8 perform similarly in terms of promoting the charge transfer and separation of CdS based on steady-state and time-resolved photoluminescence studies. At the same time, the linear sweep voltammetry and electrochemical impedance spectroscopy tests combined with the density functional theory calculations reveal that the component interfaces of NiS/Ni9S8 enable us to lower the water splitting activation energy, the charge-transfer resistance from the cocatalyst to sacrificial agent, and hydrogen adsorption Gibbs free energy. It is evidenced from this work that component interfaces of hybrid cocatalysts play a vital role in accelerating the dynamics of hydrogen evolution reactions.

Photo-induced electron transfer between carbon dots and menadione in non-ionic micelles: A triplet states study with magnetic field

Compared to homogeneous surroundings, the kinetics of ultrafast photo-induced processes gets perturbed in self-assemblies. Herein, we attempt to unveil the photophysical alterations in highly luminescent carbon dots (CDs) with menadione (MQ-Vitamin K3), in homogeneous aqueous medium and nonionic Brij-35 self-assemblies. With a series of steady-state and time-resolved studies, we report photoinduced electron transfer between the CDs and MQ for Brij-35. Host-guest-like encapsulation in micelles can severely deter the diffusion dynamics of the transient intermediates. With an external magnetic field, we trace an enhancement in the radical products with controlled diffusion and spin dynamics for Brij-35 than the aqueous surrounding.

Sources and composition of elemental carbon during haze events in North China by a high time-resolved study

Despite the implementation of stringent emission reduction measures in the past year, severe winter haze events still occurred frequently in North China, with only marginal decreases observed in elemental carbon (EC) concentrations. EC not only constitutes a fraction of particle mass but also interacts with boundary layer and influences haze formation. Given the complex composition of EC, characterizing its sources and composition during haze processes is challenging yet crucial for understanding haze formation and evolution. Here, hourly-resolution PM2.5 samples were collected during three different haze event (P1-P3) in the North China Plain to investigate dynamic changes in EC source across different haze processes. The average EC concentrations and char/soot ratios were 9.94 ± 4.80 μgC·m−3, 14.5 ± 6.93 μgC·m−3, 15.9 ± 5.54 μgC·m−3, and 2.42 ± 0.98, 2.70 ± 0.88, 2.61 ± 0.95 for P1, P2 and P3, respectively. Backward trajectory analysis showed distinct variations in EC concentration and composition under the influence of different air masses during the three haze events, with local air masses influenced days exhibiting higher EC concentrations and char/soot ratios. The char/soot ratio based diagnostic method suggested that EC was predominantly influenced by coal combustion and vehicle emissions. Further positive matrix factorization analysis suggested that biomass burning and residential coal combustion were the main contributors of EC (58 %) and played a dominant role in driving variations in EC concentrations during haze episodes. Potential source contribution function analysis results highlight that local biomass burning and residential coal combustion could be major reason for the EC elevation in different haze events. Our results provide valuable insights into the sources and composition of EC during haze events, facilitating the implementation of effective measures for mitigating both EC and PM pollution.

Steady-State and Time-Resolved Fluorescence Study of Selected Tryptophan-Containing Peptides in an AOT Reverse Micelle Environment.

The aim of this study was to demonstrate the utility of time-resolved fluorescence spectroscopy in the detection of subtle changes in the local microenvironment of a tryptophan chromophore in a confined and crowded medium of AOT reverse micelles, which mimic biological membranes and cell compartmentalization. For this purpose, fluorescence properties of L-tryptophan and several newly synthesized tryptophan-containing peptides in buffer and in an AOT reverse micelle medium were determined. It was shown that insertion of tryptophan and its short di- and tripeptides inside micelles led to evident changes in both the steady-state emission spectra and in fluorescence decay kinetics. The observed differences in spectral characteristics, such as a blue shift in the emission maxima, changes in the average fluorescence lifetime, and the appearance of environmental-dependent fluorescent species, showed the utility of time-resolved fluorescence spectroscopy as a sensitive tool for detecting subtle conformational modifications in tryptophan and its peptides induced by changes in polarity, viscosity, and specific interactions between chromophores and water molecules/polar groups/ions that occur inside reverse micelles.

The Time-Resolved Salt Stress Response of Dunaliella tertiolecta-A Comprehensive System Biology Perspective.

Algae-driven processes, such as direct CO2 fixation into glycerol, provide new routes for sustainable chemical production in synergy with greenhouse gas mitigation. The marine microalgae Dunaliella tertiolecta is reported to accumulate high amounts of intracellular glycerol upon exposure to high salt concentrations. We have conducted a comprehensive, time-resolved systems biology study to decipher the metabolic response of D. tertiolecta up to 24 h under continuous light conditions. Initially, due to a lack of reference sequences required for MS/MS-based protein identification, a high-quality draft genome of D. tertiolecta was generated. Subsequently, a database was designed by combining the genome with transcriptome data obtained before and after salt stress. This database allowed for detection of differentially expressed proteins and identification of phosphorylated proteins, which are involved in the short- and long-term adaptation to salt stress, respectively. Specifically, in the rapid salt adaptation response, proteins linked to the Ca2+ signaling pathway and ion channel proteins were significantly increased. While phosphorylation is key in maintaining ion homeostasis during the rapid adaptation to salt stress, phosphofructokinase is required for long-term adaption. Lacking β-carotene, synthesis under salt stress conditions might be substituted by the redox-sensitive protein CP12. Furthermore, salt stress induces upregulation of Calvin-Benson cycle-related proteins.

Time resolved study of temperature sensing using Gd2O3:Er,Yb: deep learning approach

This paper examines the potential applications of machine learning algorithms in the analysis of optical spectra from Gd2O3:Er,Yb thermophosphor. The material was synthesized using the solution combustion method. For data acquisition, we employed pulsed laser diode excitation at 980 nm and utilized a streak camera with a spectrograph to obtain time-resolved spectral data of the optical emission from Gd2O3:Er,Yb. To ensure data consistency and facilitate visualization, we employed principal component analysis and Uniform Manifold Approximation and Projection clustering. Our findings demonstrate that, instead of the conventional approach of identifying spectral peaks and calculating intensity ratios, it is feasible to train computer software to recognize time-resolved spectra associated with different temperatures of the thermophosphor. Through our analysis, we have successfully devised a technique for remote temperature estimation by leveraging deep learning artificial neural networks.

Form factor determination of biological molecules with X-ray free electron laser small-angle scattering (XFEL-SAS)

Free-electron lasers (FEL) are revolutionizing X-ray-based structural biology methods. While protein crystallography is already routinely performed at FELs, Small Angle X-ray Scattering (SAXS) studies of biological macromolecules are not as prevalent. SAXS allows the study of the shape and overall structure of proteins and nucleic acids in solution, in a quasi-native environment. In solution, chemical and biophysical parameters that have an influence on the structure and dynamics of molecules can be varied and their effect on conformational changes can be monitored in time-resolved XFEL and SAXS experiments. We report here the collection of scattering form factors of proteins in solution using FEL X-rays. The form factors correspond to the scattering signal of the protein ensemble alone; the scattering contributions from the solvent and the instrument are separately measured and accurately subtracted. The experiment was done using a liquid jet for sample delivery. These results pave the way for time-resolved studies and measurements from dilute samples, capitalizing on the intense and short FEL X-ray pulses.

Resonance energy transfer in electrostatically assembled donor-acceptor system based on blue-emitting InP quantum dots

Demonstration of light harvesting studies with blue-emitting quantum dots (QDs) is important to expand the scope of QDs in various optoelectronic applications including display, photocatalysis, energy and electron transfer processes, sensing, etc. Here, we report a light induced Förster resonance energy transfer (FRET) process in an all-QD based nanohybrid system containing pure-blue emitting indium phosphide (InP) QDs. A precise control over the kinetics of nucleation and growth processes resulted in the formation of environmentally friendly blue and green emitting InP QDs. The surfaces of the QDs were functionalized with oppositely charged ligands to form an electrostatically assembled donor-acceptor system based on blue and green emitting InP QDs. A large spectral overlap integral and the close proximity between the QDs in the electrostatically assembled donor-acceptor system led to an efficient FRET process (∼65%) from blue-emitting InP QDs to green-emitting InP QDs in water. Systematic steady-state and time-resolved spectroscopic studies revealed the involvement of both static as well as dynamic components in the photoluminescence quenching process. Control experiments conclusively prove the necessity of appropriately functionalized QDs and electrostatic attraction for achieving an efficient FRET process. In short, our work proves the ability of blue-emitting InP QDs to participate in an efficient FRET process, which can accelerate the development of all-QD based light harvesting systems for various optoelectronic applications.

Milk protein-based carrier system for encapsulation of dietary polyphenol rutin: Molecular-level interactions and enhanced bioactivities

The self-assembly process of proteins provides plenty of potential for redesigning and combining them into supramolecular assemblies for real-time applications. The present study demonstrates the encapsulation of dietary polyphenol rutin in β-casein (βCN) micellar cavity followed by their molecular interactions and biological implications. The prepared rutin-loaded βCN particles (DLS: 274.2 ± 3.86 nm; TEM: ∼200 nm) appeared to be smoothly spherical. Isothermal titration calorimetry (ITC) studies indicated that the encapsulation process was thermodynamically favorable and a typical example of entropy-driven hydrophobic interaction (ΔH: 38.1 kJ mol−1; TΔS = 51.9 kJ mol−1 K−1). The molecular interaction of rutin with βCN was characterized by absorption, steady-state fluorescence, and time-resolved fluorescence spectroscopic studies. The intrinsic fluorescence of βCN was quenched by rutin via a static mechanism with a favorable binding affinity. Molecular docking studies suggested the involvement of hydrophobic and hydrogen bonding interactions between the concerned entities. A sustained release mechanism followed by significant improvement in the cytotoxicity of rutin was observed after encapsulation. An in vitro digestion model mimicking gastric and intestinal phases was also employed to study the bioaccessibility. Our study may assist in formulating more efficient casein-based carrier systems to enhance the bio-efficacy of polyphenols.

Improved charge transport kinetics in PbBi2Nb2O9 photocatalysts: Comparative time-resolved recombination study with N-doped TiO2

(100) layered Aurivillius-phase perovskite single-phase PbBi2Nb2O9 (PBNO) photocatalyst was reported to be an efficient photocatalyst as compared to the conventionally known visible light photocatalyst of N doped TiO2 (NTO). We report here the specific photoluminescence studies of PBNO to understand its improved photocatalytic property. We have synthesized PBNO and NTO photocatalyst films. Further, their structural, optical and photocatalytic degradation properties have been studied. PBNO demonstrated superior methylene blue degradation as compared to NTO, under visible light photons. The steady-state and time-resolved photoluminescence (PL) studies were specially utilized at characterization tool to understand reason of the high photocatalytic activity of PBNO. We analyzed how high crystallinity of PBNO, and the longer recombination lifetime due to charge separation during photocatalytic reaction yields improved activity in PBNO as compared to NTO. Accordingly, mechanistic scheme for methylene blue photodegradation under solar light photons has been proposed. This study also indicates importance of photoluminescence study for photocatalysts.

Cell-Permeable Stimuli-Responsive Ubiquitin Probe for Time-Resolved Monitoring of Substrate Ubiquitination in Live Cells.

Dynamic monitoring of intracellular ubiquitin (Ub) conjugates is instrumental to understanding the Ub regulatory machinery. Although many biochemical approaches have been developed to characterize protein ubiquitination, chemical tools capable of temporal resolution probing of ubiquitination events remain to be developed. Here, we report the development of the first cell-permeable and stimuli-responsive Ub probe and its application for the temporal resolution profiling of ubiquitinated substrates in live cells. The probe carrying the photolabile group N-(2-nitrobenzyl)-Gly (Nbg) on the amide bond between Ub Gly75 and Gly76 is readily prepared through chemical synthesis and can be delivered to live cells by conjugation via a disulfide bond with the cyclic cell-penetrating peptide cR10D (i.e., 4-((4-(dimethylamino)phenyl)-azo)-benzoic acid-modified cyclic deca-arginine). Both in vitro and in vivo experiments showed that Ub-modifying enzymes (E1, E2s, and E3s) could not install the Ub probe onto substrate proteins prior to removal of the nitrobenzyl group, which was easily accomplished via photoirradiation. The utility and practicality of this probe were exemplified by the time-resolved biochemical and proteomic investigation of ubiquitination events in live cells during a H2O2-mediated oxidative stress response. This work shows a conceptually new family of chemical Ub tools for the time-resolved studies on dynamic protein ubiquitination in different biological processes and highlights the utility of modern chemical protein synthesis in obtaining custom-designed tools for biological studies.

High-harmonic generation in liquids with few-cycle pulses: effect of laser-pulse duration on the cut-off energy.

High-harmonic generation (HHG) in liquids is opening new opportunities for attosecond light sources and attosecond time-resolved studies of dynamics in the liquid phase. In gas-phase HHG, few-cycle pulses are routinely used to create isolated attosecond pulses and to extend the cut-off energy. Here, we study the properties of HHG in liquids, including heavy water, ethanol and isopropanol, by continuously tuning the pulse duration of a mid-infrared driver from the multi- to the two-cycle regime. Similar to the gas phase, we observe the transition from discrete odd-order harmonics to continuous extreme-ultraviolet emission. However, the cut-off energy is shown to be entirely independent of the pulse duration. These observations are confirmed by ab-initio simulations of HHG in large liquid clusters. Our results support the notion that the cut-off energy is a fundamental property of the liquid, independent of the driving-pulse properties. Our work implies that few-cycle mid-infrared laser pulses are suitable drivers for generating isolated attosecond pulses from liquids and confirm the capability of high-harmonic spectroscopy to determine the mean-free paths of slow electrons in liquids.

Time-resolved study on signaling pathway of photoactivated adenylate cyclase and its nonlinear optical response

Photoactivated adenylate cyclases (PACs) are multidomain BLUF proteins that regulate the cellular levels of cAMP in a light-dependent manner. The signaling route and dynamics of PAC from Oscillatoria acuminata (OaPAC), which consists of a light sensor BLUF domain, an adenylate cyclase domain, and a connector helix (α3-helix), were studied by detecting conformational changes in the protein moiety. Although circular dichroism and small-angle X-ray scattering measurements did not show significant changes upon light illumination, the transient grating method successfully detected light-induced changes in the diffusion coefficient (diffusion-sensitive conformational change (DSCC)) of full-length OaPAC and the BLUF domain with the α3-helix. DSCC of full-length OaPAC was observed only when both protomers in a dimer were photoconverted. This light intensity dependence suggests that OaPAC is a cyclase with a nonlinear light intensity response. The enzymatic activity indeed nonlinearly depends on light intensity, that is, OaPAC is activated under strong light conditions. It was also found that both DSCC and enzymatic activity were suppressed by a mutation in the W90 residue, indicating the importance of the highly conserved Trp in many BLUF domains for the function. Based on these findings, a reaction scheme was proposed together with the reaction dynamics.

Photo-Induced Super-Hydrophilicity of Nano-Calcite @ Polyester Fabric: Enhanced Solar Photocatalytic Activity against Imidacloprid.

The present study is pertinent to photo-induced, hydrophilic, nano-calcite grown onto the mercerized surface of polyester fabric (PF), treated with UV (10-50 min) and visible light (1-5 h) in addition to its photocatalytic application. The wicking method has been employed to select the most hydrophilic sample of fabric upon irradiation. The micrographs obtained by scanning electron microscopy, transmission electron microscopy, and high-resolution transmission electron microscopy indicated the erosions occurring at the surface of nano-calcite after UV light irradiation, maintaining the crystallinity of the photocatalyst. The surface charge has been measured for as-fabricated and irradiated nano-calcite @ PF for the development of high negative zeta potential after UV light irradiation (-24.6 mV). The irradiated nano-calcite @ PF exhibited a significant change in its contact angle, and the wetting property was enhanced to a considerable extent on UV (55.32°) and visible light irradiation (79.00°) in comparison to as-fabricated nano-calcite @ PF (137.54°). The irradiated samples of nano-calcite @ PF delineated the redshift in harvesting of solar spectrum, as revealed by diffuse reflectance spectroscopy comparative spectra. Additionally, the band gap of untreated nano-calcite was found to be 3.5 eV, while UV- and visible light-irradiated PF showed a reduction in band gap up to 2.95 and 3.15 eV upon UV and visible light irradiation. The photocatalytic efficiency of mesoporous nano-calcite was evaluated by photocatalytic degradation of imidacloprid as the probe pollutant. Higher solar photocatalytic degradation of imidacloprid (94.15%) was attained by UV light-irradiated nano-calcite @ PF. The time-resolved photoluminescence study has verified the high photocatalytic activity of UV light-irradiated nano-calcite @ PF for the generation of high concentration of hydroxyl radicals. The highly efficient reusability of a nano-calcite-based solar photocatalytic reactor has been observed for 10 cycles of treatment of imidacloprid bearing wastewater. The enhanced photocatalytic activity of UV light-exposed (20 min), superhydrophilic, nano-calcite @ PF for mineralization of pollutants suggests it to be an efficient solar photocatalyst for environmental applications.

Time-resolved cryo-EM (TR-EM) analysis of substrate polyubiquitination by the RING E3 anaphase-promoting complex/cyclosome (APC/C).

Substrate polyubiquitination drives a myriad of cellular processes, including the cell cycle, apoptosis and immune responses. Polyubiquitination is highly dynamic, and obtaining mechanistic insight has thus far required artificially trapped structures to stabilize specific steps along the enzymatic process. So far, how any ubiquitin ligase builds a proteasomal degradation signal, which is canonically regarded as four or more ubiquitins, remains unclear. Here we present time-resolved cryogenic electron microscopy studies of the 1.2 MDa E3 ubiquitin ligase, known as the anaphase-promoting complex/cyclosome (APC/C), and its E2 co-enzymes (UBE2C/UBCH10 and UBE2S) during substrate polyubiquitination. Using cryoDRGN (Deep Reconstructing Generative Networks), a neural network-based approach, we reconstruct the conformational changes undergone by the human APC/C during polyubiquitination, directly visualize an active E3-E2 pair modifying its substrate, and identify unexpected interactions between multiple ubiquitins with parts of the APC/C machinery, including its coactivator CDH1. Together, we demonstrate how modification of substrates with nascent ubiquitin chains helps to potentiate processive substrate polyubiquitination, allowing us to model how a ubiquitin ligase builds a proteasomal degradation signal.

Spectroscopic Characterization of Thiacarbocyanine Dye Molecules Adsorbed on Hexagonal Boron Nitride: a Time-Resolved Study.

Physisorption on hexagonal boron nitride (hBN) gained interest over the years thanks to its properties (chemically and thermally stable, insulating properties, etc.) and similarities to the well-known graphene. A recent study showed flat-on adsorption of several cationic thiacarbocyanine dyes on hBN with a tendency to form weakly coupled H- or I-type aggregates, while a zwitterionic thiacarbocyanine dye rather led to a tilted adsorption. With this in-depth time-resolved study using the TC-SPC technique, we confirm the results proven by adsorption isotherms, atomic force microscopy, and stationary state spectroscopy combined with molecular mechanics simulations and estimation of the corresponding exciton interaction. The absence of a systematic trend for the dependence of the decay times, normalized amplitudes of the decay components, and contribution of different components to the stationary emission spectra upon the emission wavelength observed for all studied dyes and coverages suggests the occurrence of a single emitting species. At low coverage levels, the non-mono-exponential character of the decays was attributed to adsorption on different sites characterized by different intramolecular rotational freedom or energy transfer to nonfluorescent traps or a combination of both. The difference between the decay rates of the four dyes reflects a different density of the nonfluorescent traps. Although the decay time of the unquenched dyes was in the order of magnitude of that of dye monomers in a rigid environment, it is also compatible with weakly coupled aggregates such as proposed earlier based on the stationary spectra. Hence, the adsorption leads to a rigid environment of the dyes, blocking internal conversion. Increasing the concentration of the dye solution from which the adsorption on hBN occurs increases not only the coverage of the hBN surface but also the extent of energy transfer to nonfluorescent traps. For TDC (5,5-dichloro-3-3'-diethyl-9-ethyl-thiacarbocyanine) and TD2 (3-3'-diethyl-9-ethyl-thiacarbocyanine), besides direct energy transfer to traps, exciton hopping between dye dimers followed by energy transfer to these traps occurs, which resulted in a decreasing decay time of the longest decaying component. For all dyes, it was also possible to analyze the fluorescence decays as a stretched exponential as would be expected for energy transfer to randomly distributed traps in a two-dimensional (2D) geometry. This analysis yielded a fluorescence decay time of the unquenched dyes similar to the longest decay time obtained by analysis of the fluorescence decays as a sum of three of four exponentials.